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1975 Clearance of and in patients undergoing peritoneal dialysis Robert F. Malacoff Yale University

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Recommended Citation Malacoff, Robert F., "Clearance of tobramycin and clindamycin in patients undergoing peritoneal dialysis" (1975). Yale Medicine Thesis Digital Library. 2892. http://elischolar.library.yale.edu/ymtdl/2892

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CLEARANCE OF TOBRAMYCIN AND CLINDAMYCIN

IN PATIENTS UNDERGOING PERITONEAL DIALYSIS

by

Robert F. Malacoff B.S., Columbia University, 1971

A Thesis Submitted to the Department of Internal Medicine in Partial Fulfillment of the Requirements for the Degree of

Doctor of Medicine

Yale University School of Medicine 1975

to my parents, Betty and Isidore

and to Cheryl

for all their confidence, support and love.

ACKNOWLEDGEMENTS

To Vincent T. Andriole, M.D., whose expertise, guidance and patience

proved invaluable throughout this investigation. His sincerity

and dedication to the art of teaching made this project enjoyable

as well as a learning experience.

To Frederic 0. Finkelstein, M.D., for his advice in the design of this research.

To Ernesto D. Hendler, M.D., for his assistance at the West Haven Veterans Hospital.

To The Nursing Staff of the Peritoneal Dialysis Units at the Yale-New Haven and West Haven Veterans Hospitals.

To Nancy Joyce and Alan Siniseal chi for their friendship and technical assistance in the laboratory.

To Susan Proto for secretarial help and Alan Siniscalchi for his photography.

TABLE OF CONTENTS Page

I. Introduction 1 A. Tobramycin B. Clindamycin

II. Materials and Methods 7 A. Patients B. Dialysis C. Administration of D. Protocol E. Assay (i) Tobramycin (ii) Clindamycin

III. Data Analysis 11 A. Serum and Peritoneal Dialysate Levels B. Clearance: C C. Amount of Antibiotic Removed D. Half-Life: T-j^ E. Volume of Distribution: V,, (V.), F. Area under the Curve: A G. Error Analysis

IV. Results 18 A. Tobramycin B. Clindamycin

V. Discussion 21 A. Effect of Peritoneal Dialysis on Urea and Creatinine Disposition B. Tobramycin (i) Systemic (ii) Peritonitis C. Clindamycin

VI. Conclusions 38

VII. Tables, Figures 39

VIII. Appendix

I. INTRODUCTION

Peritoneal dialysis has long been used as an effective mode of therapy for both acute and chronic renal failure. Because of frequent hospitalization, individuals maintained in this way are often threatened with both local and systemic infection requiring treatment with broad-

spectrum and species-specific antibiotics. Tobramycin and clindamycin

are antimicrobials that fall into the above categories. However, because of the potential toxicities of these agents, rational therapeutics demand an accurate knowledge of drug disposition, since the additional modality of peritoneal dialysis places another variable on the clinical situation, thereby necessitating possible alteration in drug dosage. Because of

the lack of data in this area, it is the purpose of this investigation to examine the and potential use of these agents in

this patient population.

A. Tobramycin

Gram-negative bacilli constitute a frequent cause of serious infection

in hospitalized patients. The antibiotics have the broadest

spectrum of antibacterial activity against these organisms. Nebramycin, an antibiotic complex of at least 7 factors, was first described by Stark, 83 et al, in 1967 and is a member of the that also includes , kanamycin, and . Fermentation biosynthesis utilizing tenebrarius5,38:>66 produces the elemental parts89 of which factor 6, tobramycin, has the greatest in vitro activity. Its 47 molecular formula is C-jgH^yN^Og*BH^O and it displays chemical behavior

similar to that of other aminoglycosidic agents.

- 1 -

Tobramycin has excellent antibacterial activity against aeruginosa and many of the Enterobacteriaceae.^5^5^5^ Most strains of Serratia, Providence, Streptococcus and Diplococcus pneumoniae are 23 resistant to attainable serum levels of tobramycin and although some 5 23 investigators report excellent anti- activity, ’ g others have found few isolates to be susceptible.

Although the in vitro spectrum of activity appears to be similar 90 to that of gentamicin, the chief advantage of this agent would appear to be its greater activity against Pseudomonas. 9 Simon, et al, studied the in vitro activity of tobramycin against 100 isolates of this organism and found the MIC's to range from 0.63 to 1.25 mcg/ml for 81% of the isolates, whereas for gentamicin 85% were inhibited by concentrations of 1.25 to 2.50 mcg/ml. Since the therapeutic response to Pseudomonas 16 17 infection has been inadequate in some cases, ’ administration of tobramycin in identical dosage might be more efficacious.

Synergy between and aminoglycosides against enterococci 52 57 is well known. ’ Although penicillin plus gentamicin has been shown to have excellent in vitro activity against all strains of enterococci 58 97 tested, 5 a significant number are resistant to the synergy of penicillin 56 82 59 plus streptomycin or kanamycin. ’ Moellering, et al, compared combinations of penicillin plus gentamicin and tobramycin against 27 strains of enterococci isolated from blood culture. It was found that although tobramycin was synergistic against all strains of Streptococcus faecal is, it was ineffective against the four strains of S_. faecium tested.

The combination of penicillin plus gentamicin was synergistic against all.

- 2 -

The toxicity of the aminoglycosidic group of antibiotics is well known and consists of both nephro- and . Ototoxicity is comparable to gentamicin and consists mainly of vestibular damage.

Renal toxicity was studied by Wick and Wells'^ who found tobramycin less nephrotoxic than gentamicin. Overall, tobramycin is considered to have a level of toxicity similar to that of kanamycin, but less than either neomycin or gentamicin.

Several investigators have studied the effect of dialysis on serum levels of the aminoglycosides, but the data is far from complete.

Atkins, et al J documented the effect of peritoneal dialysis on the 81 half-life and clearance of kanamycin, while Smithvas, et al, made similar studies with gentamicin. The clearance and half-life of both 50 tobramycin and gentamicin were determined by Lockwood and Bower in anephrics before and after hemodialysis. However, except for the report 98 of one patient by Weinstein, et al , there is no information available regarding the disposition of tobramycin in patients undergoing peritoneal dialysis.

B, Clindamycin 53 Clindamycin [7(S) Chioro-7-deoxylineomycin] is an analogue of from which it differs in the replacement of a hydroxyl group on C7 for a 54 chloride. Although the anti-bacterial spectrum of the two agents is similar, clindamycin has been shown to have greater in vitro and in vivo antibacterial activity against gram-positive aerobes, and gram-positive 4 45 51 54 85 and gram-negative anaerobic pathogens, including Bacteroides fragilis. ’ ’ ’ ’

Clindamycin phosphate is the water soluble ester and parenteral preparation of clindamycin- The phosphate is rapidly hydrolyzed to

- 3 - biologically active free clindamycin and elimination is mainly via 20 hepatic and extra-renal mechanisms. Prolonged half-life, but normal 92 serum levels have been reported with impaired liver function.

Modern anaerobic techniques permit the isolation of fastidious 61 anaerobes in many clinical settings. Aerobes, facultative and anaerobic species have been implicated as pathogens in lung abscess

(often 2° to aspiration), empyema, pelvic abscess, peritonitis, bone and wound infection. 5 The prominence of anaerobes, in particular Bacteroides, is not surprising considering these organisms 72 comprise the majority of the flora found in the upper respiratory tract, 32 31 large bowel, and female genital tract. Bacteroides bacteremia is 24 no longer an uncommon occurrence. 45 In vitro studies by Kisi a k have shown clindamycin (median MIC

0.19 mcg/ml) to be more active than lincomycin, and against 40 isolated strains of B. fragilis. Excellent clinical response to clindamycin therapy has been documented by several 4 30 49 76 observers. 555 it should be noted, however, that patients with abscess formation frequently relapse. Although certain cases require surgery, infection with multiple organisms is often the cause. In situations where both Enterobacteriacae and anaerobes are present, clindamycin alone 37 is probably not sufficient.

Clindamycin is without apparent nephro-, hepato-, or ototoxicity, 92 However, transient leukopenia and eosinophilia along with rash, nausea and vomiting^ have been reported. Although preliminary studies^ indicated that clindamycin might have fewer gastrointestinal side effects than the parent compound lincomycin, reports of diarrhea and drug-induced

_ 4 _ colitis began to accumulate as use of the drug became more widespread.

Early reports listed the incidence of mild diarrhea varying from 4 to 21 27 33%. ’ In these cases, the onset was usually abrupt, and bloodless watery diarrhea without fever or leukocytosis was characteristic. 12 However, in 1973, Cohen, et al, reported 3 cases of pseudomembranous colitis. Patients manifesting this entity were febrile, had marked leukocytosis, and displayed proctosigmoidoscopic and roentgenographic evidence of severe mucosal ulceration, pseudomembrane and pseudopolyp 93 formation. The course of such patients was variable but in most cases was protracted, requiring hydration and often both parenterally and per rectum. Whether opiates aggravate the syndrome is an area of 40 controversy. Most patients have not been seen to relapse after recovery.

Briefly, pseudomembranous enterocolitis is characterized by inflammation and necrosis of the mucosa of the bowel. 5 The cause is not known but the syndrome has been associated with heavy metal poisoning, altered blood supply to the gut, post-operative states, staphylococcus g overgrowth, obstruction, and various antibiotics, including lincomycin, 72 46 22 ampicillin, L tetracycline, D chloramphenicol, L and neomycin. The syndrome may be clinically and roentgenographically indistinguishable from inflammatory 13 or vascular bowel disease. As noted above, the etiology of the disorder is not known. However, of the possibilities that have been suggested 60 one includes freed bacterial antigen interacting with host mucosa.

The report^ of positive anti-nuclear factor in 2 of 4 patients with clindamycin-induced colitis, and the subsequent disappearance in one, again implies an immune mechanism.

The original description of this drug-induced colitis have been

- 5 -

18 19 28 84 9Q 1D4 subsequently confirmed in the literature. 9 9 9 9 9 Current evidence would, therefore, indicate that clindamycin is a therapeutic agent with potentially serious toxicity and should not be prescribed for minor infection where another, less toxic substitute will do.

There are several studies on the use of clindamycin in patients with normal 21 and impaired renal function. Joshi and Stein 44 documented the serum half-life in uremics not on dialysis, while Cimino, et al,^ studied the pharmacokinetics in patients on hemodialysis. To date there have been no reports of half-life and clearance measurements of clindamycin in patients undergoing peritoneal dialysis, although Reinarz and McIntosh 68 investigated the effect of azotemia, hemodialysis and peritoneal dialysis on the parent compound lineomycin.

- 6 -

II. MATERIALS AND METHODS

A. Patients

Outpatients of the Yale-New Haven and West Haven Veterans Administration

hospitals with chronic renal failure comprised the patient population

studied. All had been maintained on chronic peritoneal dialysis for at

least 6 months, and had creatinine clearances less than 3 ml/min. None

were septic, nor had any received antibiotics during the 2 week period

prior to study. Informed consent was obtained from each patient after

a detailed description of the procedures and potential complications.

B. Dialysis

All patients studied had permanent indwelling cannulae in place.

Dialysis solutions (Dianeal 1.5 or 4.25% dextrose) were prewarmed to body temperature prior to infusion. Heparin was not added to the dialysate

inflow.

C. Administration of Antibiotics

After a volunteer was selected for either the tobramycin or clindamycin

study, the appropriate antibiotic was diluted in 100 ml of 5% dextrose

in water, and administered intravenously over 20 minutes. The dosage for

tobramycin and clindamycin were 1 mg/kg and 600 mg respectively.

D. Protocol

After taking a control serum specimen, the appropriate antibiotic was administered as described above. The beginning of the infusion was

considered to be time zero. Another serum sample was drawn 5 and 30 minutes

after the end of the infusion and dialysis was begun 30 minutes later.

- 7 -

Dialysis was performed according to the following schedule: 10 minutes

to run into the peritoneal cacity, 20 minutes to equilibrate, and 30 minutes to drain. The flow rate was 2 liters/hour.

The dialysate from exchanges 1 through 7 and exchange 12 were collected in 2 liter dialysate bottles that had been previously autoclaved at 120°C, and serum samples were taken at 1.5, 2.5, 6.5, 7.5, and 12.5 hours after the beginning of the study (time = 0). After the completion of the 12th exchange, which coincided with the 12th ancj f-jnal hour of the study, dialysis was then performed as per the dialysis unit.

For clindamycin, serum samples were taken at 1.5, 3.0, 6.0, 9.0, and 12 hours. Dialysate was collected in the same manner as for tobramycin.

E. Antibiotic Assays

The assay for both tobramycin and clindamycin utilized the agar- diffusion principle. Wells of uniform size were cut in agar evenly seeded with an organism sensitive to the antibiotic to be assayed. When serum or dialysate containing antibiotic was placed in a well, a zone of inhibition surrounded by a background of dense bacterial growth resulted (Fig. 1). 102 By comparison to known standards, unknowns could be determined.

Antibiotics: 9 (i) Tobramycin - modification of Micro-Agar plate for Tobramycin Assay, a. Materials:

Plastic Petri Dishes - 150x15 mm (Lab-Tek No. 4028) Capillary tubes - Drummond "Microcaps": 10 microliter pipettes. (Drummond Scientific Co.) 3 rnn cal ibrated 1 oop Caliper with vernier dial (Glogau & Co.) Modified Trypticase Soy Agar (TSA) - 26.66 gm TSA base/1000 ml; pH = 7.3 (Difco)

- 8 -

TSA slant Brain Heart Infusion Broth (BHIB) - (Difco) Pooled normal human serum Magnifier-Viewer - (National Instrument Laboratories, Inc., Rockville, Md.) 12 gauge Jel co b. Organism

Bacillus globigii, an unclassified spore-former. Maintained on TSA slant @ 4°C. with transfer to new media every 2 weeks. c. Method

1) Calibrated loop was scraped along surface of TSA slant and organisms were inoculated into 30 ml of BHIB contained in a 50 ml Ehrlenmyer flask. Incubation for 6 hours @ 37°C yielded 10' - 10^ organisms/ml.

2) 36 ml of melted TSA that had been cooled to 47°C in a water-bath, plus 3.0 ml B_. globigii were poured into a petri dish and swirled until adequate mixing had been achieved. Plates were allowed to cool and set at room temperature with the lids ajar for 20 minutes.

3) Plates were stored 0 4°C until use for up to 5 days.

4) Wells were punched in the agar with a 12-gauge Jelco (with the bevel ground off) attached to low suction.

5) Antibiotic standard - Working laboratory standard: Equivalent to 1000 meg base per ml. Eli Lilly and Co. XU 5074 AMX. Assay standards were made in pooled normal human serum at the following concentrations (mcg/ml): 20.0, 10.0, 5.0, 2.50, 1.25, and were stored without loss of accuracy for up to 3 weeks. Peritoneal dialysate for use in making standards was collected during the week prior to study. All serum and dialysate unknowns were stored at -4°C along with the standards, and were assayed within 2 days of the study.

6) Wells were filled until the meniscus was visible at the rim. Flooded or underfilled wells were discarded. A full set of standards accompanied unknowns on every plate and plates were done in duplicate.

7) Plates were then incubated for 6 hours @ 37°C.

8) Zones of inhibition were measured with the aid of both a viewer equipped with a magnifying stage, and vernier calipers.

- 9 -

91 (ii) Clindamycin - Modification of Serum Clindamycin Assay Procedure.

Assay similar to that outlined for tobramycin, and differs only as noted be! ow. a. Materials:

Capillary tubes - Yankee No. 1021 Microhematocrit tubes/Plain. 75x O.D. 1.50 mm (I.D. 1.10 mm). (Clay Adams). Penassay Broth (PAB) - B243 (Difco) Penassay Seed Agar (PAA) - B263 (Difco) Nutrient Agar (NA) - B1 (Difco): NA slant Stainless steel punch - O.D. 0.4 cm b. Organism

Sarcina lutea - ATCC 9341. maintained on NA slant 0 4°C with transfer to new media every 2 weeks. c. Method

1) Inoculum into PAB. Incubated for 16 hours @ 37°C.

2) 36 ml melted PAA plus 3.0 ml S_. 1 utea (16 hour culture).

4) For antibiotic assay in the range 5 mcg/ml to 20.0 mcg/ml, 12-gauge Jelco punch was used to make wells. A larger punch (0.4 cm O.D.) was used for determinations in the range 0.5 mcg/ml to 5.0 mcg/ml .

5) Antibiotic standards - Working laboratory standard: 1000 mcg/ml of cl indamycin-2-P04 8760-AJS-115-11 (841.5 meg base equivalents/mg). Assay standards were made in pooled normal human serum at the following concentrations (mcg/ml): 22.5, 7.50, 3.76, 1.88, and .98. Standards were treated with phosphate buffer 0 pH = 8.0 in order to allow measurement of "free clindamycin."21

10 -

III. DATA ANALYSIS

A. Serum and Peritoneal Dialysate Antibiotic Levels

The diameter of the zones of inhibition of growth were measured to the nearest 0.1mm with vernier calipers and the magnifying viewer. When solving graphically, triple cycle semi 1ogarithmic paper is used. The concentration of the antibiotic standard (mcg/ml) is plotted on the y-axis

(ordinate), and the corresponding zone sizes on the x-axis (abscissa).

The best straight line approximating these points is drawn, and using the zones of inhibition they produce, the unknowns can then be extrapolated from the graph. The range of the assay is 0.6 to 20.0 mcg/ml.

In an attempt to increase both the speed and accuracy of the above analysis, the Monroe Statistical Calculator (model 1930) was utilized to perform linear regression analysis on the standard data and thus provide an equation of the form y = mx + b describing the best straight line for that data. In this equation

y = log (concentration of antibiotic mcg/ml) m = slope x = diameter of zone (cm.) b = y intercept when x = 0

The calculator provides both m and b. Therefore, if the diameter of the zone of inhibition for an unknown is substituted into the equation then

y = mw + b = z x = w

Z represents a number that is a logarithm. In order to transform this value back to a concentration in mcg/ml, the inverse function of log must be allowed to operate. If v is the unknown concentration, then

y = z = log v ey = ez = elo9 v = mcg/ml

11

In this way, all the assay results for both tobramycin and clindamycin were evaluated. As the determinations were done in duplicate, serum and dialysate values were expressed as the mean ± the standard deviation (S.D.)

B. Clearance

In renal physiology, clearance is considered to be the smallest volume of plasma from which the kidneys can obtain the amount of the 75 substance excreted per minute. In this study, a similar definition can be used and the following equation results:

C = (D x V)/S

where C = clearance (ml/min) D = dialysate concentration (antibiotic: mcg/ml; creatinine or urea: mg%) V = volume of dialysate (ml/hr) S = serum concentration (mcg/ml or mg% as above)

As outlined in the protocol, the duration of each exchange was 1 hour. V was determined by measurement of the total dialysate drainage for that exchange period. S was determined from a serum sample taken at the midpoint of that exchange period and was considered to be an approximation of the mean serum level of urea, creatinine or antibiotic during that exchange. The serum decay curve of the antibiotic was utilized to estimate the mean serum antibiotic level for exchanges where no serum sample was taken.

The peritoneal clearance of urea, creatinine and administered antibiotic was calculated.

C. Amount of Antibiotic Removed

This quantity was calculated by the following equation:

- 12

V' x D = A

where V' = volume of dialysate (ml) D = dialysate antibiotic concentration (mcg/ml) A = amount of antibiotic removed/exchange

The total antibiotic removed over the 12 hours of dialysis was estimated.

It should be noted that exchanges 8 through 11 were not collected. An approximation of the antibiotic concentration was made by taking the mean value of exchanges 7 and 12.

D. Half-Life: T1/2

The pharmacokinetic behavior of administered drugs can be thought of in terms of several types of compartmental models:

(i) 1-Compartment: Assumes instantaneous distribution within a single compartment.

i.v. COMPARTMENT BIOTRANSFORMATION DOSE AND EXCRETION

Fig. 2

(ii) 2-Compartment: Assumes instantaneous distribution within a central compartment (e.g. blood, ECF etc.), and a slower distribution into a peripheral compartment (e.g. intracellular space).

kJ2^ I.V. CENTRAL COMPARTMENT PERIPHERAL COMPARTMENT DOSE NO 1 NO. 2 k21

ik‘* = kel BIOTRANSFORMATION AND EXCRETION NO. 3

Fig. 3

13 -

(iii) 3-Compartment: A central compartment, as above with distribution into 2 peripheral compartments at differing rates.

Although the above models are useful in explaining the kinetics of

drug disposition, it is important to note that in some cases, there

may be little physiologic basis for their actual existence.

Drug distribution in the most complex of systems can theoretically

be described by a multi-compartmental model. However, although Riegelman, 69 et al , suggested that a bi- or tri-exponential function could accurately

describe distribution of an administered drug, it was Sharney and co- 78 workers who were able to mathematically reduce a large number of

interchanging pools to a 2 or 3 compartment model.

We can, therefore, attempt to describe the kinetics of the present 69 study by the 2-compartment open system as outlined by Riegelman. Here, the serum concentration Cp at any time t is given by the equation:

Cp = A e"at + B e"bt

The coefficients A and B, along with the hybrid rate constants a and b 86 can be determined by graphical analysis, or by computer determination

(BMDP3R - Nonlinear regression analysis - IBM 360. See Appendix)

When adequate numbers of serum samples are taken after the intravenous

administration of a drug, an equation of at least 2 exponential terms

in the form seen above is obtained. Although it is usual practice to

call b the elimination rate constant, it can be seen from Fig. 3 that

k -j is the appropriate constant, a and b can be shown to be hybrid rate 69 constants , their magnitude being dictated by the rate constants

participant in the overall kinetics of the system. The actual relation

between k^ and b is given by

kei = Cp0/ (A/a + B/b)

14 -

94 Wagner, et al, showed that when the volume of the peripheral compartment was much greater than the central , and the rate constant k^ much greater than , the T-^ estimate 0.693/b will overestimate the half- life, b is, therefore, a function of both Vcentral/Vperiphera) and K,2/keK

Thus, when b is not a good estimate of k^ , T-^ is best calculated by the equation

T-j - 0.693/ke-| where

kel = ab (A + B)/(Ab + Ba)94

In the present study, the coefficients and rate constants of the

. b "t relation Cp = Ae" z + Be-0 were determined by either graphical or computer analysis to the same degree of significance. The calculated half-life for each drug is reported as:

(i) T-i /ob - The parameter b estimates the slope of the terminal / log-linear section of the serum decay curve and is related to the T,/? by the following expression: T-,= 0.693/b. ' Determination of half-life by 'this method assumes monoexponential decay.

(ll) T1/2kel- Utilization of all the coefficients and rate constants of the bi-exponential formulation result in determination of k_n , the elimination rate constant. This constant 'el is related to T-^ by the expression: T-j^^el = 0,693/ k i el

E. Volume of Distribution

The volume of distribution (L), is simply a proportionality constant used in pharmacokinetics, and has no real physiologic significance. One definition is, that volume of fluid into which the drug apparently distributes 86 with a concentration identical to that in blood. Vd can be calculated in several ways, the most common being graphically. Analysis by this method assumes monoexponential decay during elimination and simply involves the extrapolation of the straight linear terminal portion of the decay curve

- 15 -

back to time = 0. This results in determination of the serum concentration

at this time, and is designated Cp°. can then be calculated by the

rel ation:

= D/Cp° where D = administered dose (mg).

If, however, the decay curve cannot be accurately estimated by a single exponential function, then it must be assumed that at least a 2-compartment model is necessary to describe the system. The of the two compartment open system is more complicated and can be determined 86 by the following equation:

(Vd)b = Da/(Ba + Ab) where D = administered dose

a,b = hybrid rate constants

A,B = exponential coefficients

Vj is useful in that it is inversely proportional to the peak serum concentration Cp° and can be used to estimate this value at varying dosages.

F. Area Under The Curve: A

The administered dose can be represented by the area under the intravenous concentration-time curve. This can be calculated by either taking the integral of the function describing the serum decay (with appropriate time limits), or by numerical integration using the trapazoidal 86 rul, e.

In this investigation, the mean values for serum levels were plotted and used to construct a mean serum decay curve. The area below the curve from 0 to 12 hours was determined by the trapazoidal rule.

G, Error Analysis

All serum and dialysate assays were done in duplicate on each plate.

Each unknown was done on duplicate plates in order to insure reproducibility

- 16 - of results. Plate-to-plate coefficient of variation was - 10%. All values are, therefore, reported as the mean of those obtained on two independent determinations. The error is reported as + the standard deviation of the mean (SD).

All other values (e.g. C, V^, Tetc.) are reported as the mean

± the standard error (SE).

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IV. RESULTS

There were no complications during the present investigation except for patient #4 who accumulated approximately 5 liters in his peritoneal cavity during the 12^ exchange of the tobramycin study. The fluid subsequently drained without incident.

A. Tobramycin

1) Serum and Peritoneal Dialysate Antibiotic Levels: In the 5 patients studied, the mean peak serum concentration (Table 1, Fig. 4) was

4.66 mcg/ml (range: 3.29 - 7.36) recorded at 5 minutes post infusion.

After 12 hours of dialysis, at a flow rate of 2 liters/hour, this level fell to 1.64 mcg/ml (range: 1.26 - 2.10). The mean peritoneal dialysate concentration (Table 2) was 0.91 mcg/ml (range: 0.79 - 1.07) over the 12 hours of dialysis.

2) Clearance: The individual values for the clearance of tobramycin are listed in Table 2. The mean clearance was 14.98 ml/min (range: 12.31 -

20.01). Similar calculations for urea and creatinine yield values of

26.82 ml/min (range: 25.08 - 30.55) and 23.99 ml/min (range: 23.77 - 24.50) respectively (table 10). The ratios of the respective clearances along with pre- and post-dialysis serum levels of urea and creatinine are given.

3) Total Amount of Antibiotic Removed by Dialysis (Table 2): The mean quantity of antibiotic removed after 12 hours of dialysis was 21.00 mg (range: 17.30 - 25.43). This resulted in 33.9% removal of the initial

1 mg/kg dose.

4) Half-life: T(Table 3): Graphical and computer analysis yielded the coefficients A, B, a and b (Table 6). Utilizing these values two

18 -

estimates of Twere obtained:

(i) Ti/2^5 which utilized the slope of the terminal log-linear

segment of the serum decay curve, was 16.08 hours (range: 8.88 - 19.25).

(ii) Ti/2^el ’ whl'ch was calculated assuming applicability of the

2-compartment model, was found to be 10.74 hours (range: 8.90 - 13.05).

The T-j/2 calculated from the tail portion of the average serum decay

curve (Fig. 4) was 14.44 hours.

5) Volume of Distribution: V^, (V^)^ (Table 4): The mean for the 5 patients studied was 21.40 liters (range: 16.07 - 31.28) which

represented 34.34% of total body weight (BW) (range: 27.93 - 44.10).

(Vd)b» which is based on the 2-compartment model, was calculated to be

22.93 liters (range: 15.71 - 32.77) and represented 36.35% of BW (range:

28.83 - 46.15).

6) Area under the Serum Decay Curve: A-p For the 12 hours of study,

Ay was found to be 28.54 (mcg/ml)(hour).

B. Clindamycin

1) Serum and Peritoneal Dialysate Antibiotic Levels: In the 3 patients studied, the mean peak serum concentration (Table 8, Fig. 5) was 15.41 mcg/ml (range: 13.78 - 16.82) recorded at 5 minutes post infusion. After

12 hours of dialysis, at a flow rate of 2 liters/hour, this level fell

to 1.39 mcg/ml (range: 0.66 - 2.58).

Clindamycin levels were determined on dialysate from exchanges 1, 3,

and 6. Only exchange 1 had detectable anti-bacterial activity (Table 5).

The mean dialysate concentration for this exchange was 1.81 mcg/ml (range:

1.42 - 2.53).

2) Clearance: The mean clearance for the three patients studied was

19 -

4 ml/min during the first exchange. Urea and creatinine clearance were not determined during this study. Pre- and post-dialysis serum urea and creatinine levels are listed in Table 8.

3) Total Amount of Antibiotic Removed by Dialysis: The mean quantity of antibiotic removed during the first exchange was 3 mg.

4) Half-Life: T-^ (Table 5): Graphical and computer analysis yielded two estimates of T

(i) /2b’ utilized the slope of the terminal log-linear segment of the serum decay curve, was 4.55 hours (range: 2.22 - 6.42), and

(ii) Ti/^ei , calculated assuming applicability of the 2 compartment model, was 2.81 hours. The T-^ determined from the tail portion of the average serum decay curve (Fig. 5), was 6.79 hours.

5) Volume of Distribution: Not determined in the present investigation.

6) Area under the Serum Decay Curve: A^: A^ was found to be 49.88

(mcg/ml)(hour) for the 12 hours of study.

- 20 -

V. DISCUSSION

A. Effect of Peritoneal Dialysis on Urea and Creatinine Disposition

The clearance of urea and creatinine in patients undergoing peritoneal

dialysis was documented in four of the five patients who underwent study with tobramycin (Table 10). The mean values for urea and creatinine clearance were 26.82 and 23.99 ml/min respectively. These values are greater than the clearances in a similar patient population reported by

Nolph, et al, D (Table 11). This finding may be secondary to the inter¬ mittent use of hypertonic dialysate (Dianeal 4.25% dextrose) during the present study. It has been demonstrated^3 that ultrafil tration across the peritoneal membrane is enhanced with the use of hypertonic dialysis solutions. Henderson and Nolphi /D concluded that the alteration in peritoneal transport was secondary to a significant increase in membrane permeability, and additionally showed that increased transperitoneal transport persisted during subsequent exchanges that utilized isotonic dialysate. 63b The study reported by Nolph, et al, u utilized isotonic dialysate, and it is, therefore, understandable that the clearances documented in the present study are greater than previously reported values.

B. Tobramycin

It was stated at the outset that although there was little data on the use of tobramycin in patients undergoing peritoneal dialysis, the pharmacokinetics of the drug in renal disease were known. Naber, et al,

found peak serum values, after an initial dose of 1 mg/kg administered

intravenously, in normals and patients with impaired renal function (highest

- 21 creatinine = 3.8 mg%) to be approximately 6.8 and 9.2 mcg/ml respectively.

In contrast, the present study found peak levels of 4.66 mcg/ml (Fig.4 ) in 4 patients who were essentially anephric (creatinine clearance - 3 ml/min). This difference would appear to be significant. One possibility that serum levels are not as high as would be expected from previous studies may be explained by noting that although tobramycin appears to distribute rapidly into a volume comparable to the extracellular space 80 in patients with normal renal function, there is probably distribution into a larger space in patients with significant renal impairment. This greater volume of distribution is most likely secondary to penetration of the drug into the intracellular compartment, 80 Simon, et al , compared the pharmacokinetics of tobramycin and gentamicin in normals. The for tobramycin was found to be 16.9 liters by constant infusion studies. This value was not statistically different from that obtained for gentamicin, and it can therefore be concluded that both antibiotics distribute into a compartment slightly larger than the extracel 1 ular space. Although there is no data reporting the of tobramycin in anephrics, such information is available for gentamicin. 36 Gyselynck determined the of gentamicin in several patients with inulin clearances of less than 7 ml/min, and found their mean to be 41.0% BW

(range: 32.9 - 51.9) by single intravenous injection studies similar to those performed in the present investigation. Clearly, the for patients with severe renal impairment is much greater than that observed for normals, and may approach a volume eaual to total body water.

Based on the above data for gentamicin, it could be postulated that similar values would be obtained for tobramycin in patients with severe

- 22 renal impairment. The results of the present study substantiate this hypothesis in that the determined graphically in 5 patients studied was found to 21.40 liters (34.34% BW). Therefore, a significantly larger volume of distribution exists in functionally anephric patients, when compared to the in normals as described above. This being the case, the lower than expected peak serum levels are understandable and can be described by the relationship:

Cp° = D/Vd where D = administered dose (mg)

As increases, the peak serum level falls. 62 It must be noted, however, that Naber, et al, determined the in patients with renal impairment (highest creatinine = 3.8 mg%) and found no statistical difference from that obtained in normals. It is concluded that large volumes of distribution are seen only with severe renal failure. This idea is corroborated by the data presented by 36 Gyselynck for gentamicin in that very large volumes of distribution were seen only with extensive renal dysfunction.

The above discussion of increased distribution space found in the present study can be criticized because simultaneous studies with inulin were not performed. However, because of the similarity in behavior of tobramycin and gentamicin concerning the parameter V^, the explanation given follows logically from the known data. Further investigation might attempt to more fully delineate the in patients with severe loss of renal function.

Another possibility for the finding of lower peak serum levels is difference in assay technique. Control samples and assays done in duplicate were used in an effort to minimize such variation.

- 23 -

Several antibiotics have been studied in patients undergoing peritoneal 29 35 73 79 dialysis. 5 ’ 9 Of the aminoglycosides, kanamycin and gentamicin have been the most extensively characterized. Atkins, et al J determined the effect of dialysis on kanamycin disposition in anephrics. Over a period of dialysis lasting 22 hours, at a flow rate of 3.5 liters/hour

(range: 2.1 - 4.5), 32l of the administered dose was removed at a mean clearance of 8.3 ml/min. Half-life of the drug was reduced from 84 hours to 12. This data indicates the need for alteration in drug dosage schedules in order to maintain adequate serum antibiotic levels. The above study both corroborated and expanded on the earlier reports concerning 35 kanamycin by Greenberg, et al .

The effect of peritoneal dialysis on the distribution of gentamicin 27 in patients with and without peritonitis was studied by Smithvas, et al.

Of those patients with documented peritonitis, the passage of gentamicin from serum to dialysate was found to be quite variable. Therapeutic levels of antibiotic were achieved in the peritoneal dialysate in 5 of

8 patients after 36 - 48 hours without evidence of serum accumulation.

These patients were receiving 80 mg intramuscularly every 12 hours. Dialysate levels in these patients ranged from .70 to 3.90 mcg/ml, with a mean at

48 hours of 2.0 mcg/ml. On the other hand, 3 of the patients studied developed excessive serum levels (> 10.0 mcg/ml). Only 2 patients without 81 peritonitis were studied by Smithvas and co-workers, and while neither developed therapeutic dialysate concentrations after 48 hours of a dosage schedule identical to that for patients with peritonitis, one did develop toxic serum levels (15.5 mcg/ml).

The data shows removal of gentamicin in this patient population to

- 24 - < be a function of the degree of peritoneal inflammation. Clearances varied from 7.9 ml/min to 12.4 ml/min with corresponding half-lives of 15.0 to 5.3 hours in 3 patients with clinically documented peritonitis.

The amount of drug removed ranged from 40 to 70 mg/day. In one of the

2 patients studied without peritonitis, the clearance was calculated

to be 4.9 ml/min, the removal rate 10.5 mg/day, and the half-life 28.5

hours. Summarizing, the removal rate in patients without peritoneal

inflammation was 15 to 25% of that seen with peritonitis and the T-^ 27 was prolonged 2 to 5 times.

It should be noted that the above study has several limitations

in that much of the data was collected on less than 3 patients and dialysis was not uniform over the period of study. Approximately 2 liters were exchanged each hour with equilibration time varying from 0 to 20 minutes. Lastly, the calculation of serum half-life assumed monoexponential decay.

Although there are no well controlled studies of the peritoneal 98 clearance of tobramycin anephrics, there is a report by Weinstein, et al, of one patient who first received gentamicin, and then tobramycin for extensive Pseudomonas pneumonia while being maintained on peritoneal dialysis for acute tubular necrosis. Dialysate antibiotic levels were

reported between 0.5 and 1.5 mcg/ml. It should be noted, however, that this particular patient retained some degree of renal function during the study, and achieved urinary concentrations of the drug in the range

16 to 49 mcg/ml. It was estimated that 48 hours after a 90 mg initial

intramuscular dose, approximately 35 mg underwent renal clearance while 55

mg was removed by peritoneal dialysis. However, this situation was poorly

- 25 -

controlled by definition in that the use of tobramycin was limited to one patient who was critically ill, had received previous antibiotics, and retained some degree of renal function. In addition, dialysis exchanges were performed every 1 to 2 hours with 2 liters of dialysate 43 with added heparin. Jackson reported that heparin, in sufficient quantity, led to inhibition of aminoglycoside antibacterial activity.

Clearly such action would interfere with the bacteriologic assay as described earlier. These observations make it difficult to make a generalized statement about the efficacy of peritoneal dialysis in removing tobramycin.

The Tof tobramycin in anephric patients not on dialysis as 50 determined by Lockwood and Bower was 53.4 hours. In patients with creatinine clearances of 9.5, 5.0 and less than 2 ml/min, the T-^ for each was 19.5, 36.4 and 56.0 hours respectively. They additionally reported identical half-lives for gentamicin and tobramycin in anephric patients.

The cumulative data of previous studies is summarized in Table 7.

Clearly, differences exist between the three antibiotics listed, but some similarities are evident. To begin with, the results of the present study show the effect of peritoneal dialysis on tobramycin half-life to be similar to that seen with kanamycin in the absence of peritonitis.

Comparison to gentamicin reveals half-life and clearance similar to that seen in patients with peritoneal inflanimation.

Looking more closely at the result of the present study, a significant reduction in serum T^^ 1S seen. When determined using the terminal log-

linear portion of the serum decay curve, the mean T-^b for 5 patients was

- 26

16.08 hours (Table 3). Comparison to the value of 53.4 hours in anephrics

indicates a significant reduction of T^ resulting from dialysis. As discussed in the section on data analysis, calculations utilizing b only may overestimate the true T-j^ ^ assuming that the serum decay curve is monoexponential. When plotted semilogarithmically the collected data shows this type of serum decay in antibacterial activity only after several hours. To ignore this early portion of the decay curve would result in unfair bias of the data because in some cases, this period of time represents a significant portion of the overall period of study.

When the 2-compartment open system was used to analyze the data, the mean T-^ °f 4 patients, calculated from the coefficients and hybrid rate constants of the equation y = Ae"at + Be-^ (Table 6), was 10.74 hours. However, regardless of the method used, the results indicate significant removal of the drug and reduction of serum half-life.

As stated earlier, the T-^ obtained for tobramycin in the present study is comparable to that seen for gentamicin in patients with peritoneal inflammation (gentamicin T-^ range: 5.3 - 15.0 hours). This is sub¬ stantiated by the similarity of clearance values for both drugs (tobramycin

14.98 ml/min, gentamicin: 7.9 - 12.4 ml/min). Comparison to the single patient receiving gentamicin who did not have peritoneal inflammation, shows the T-j ^ of 28.5 hours to be significantly prolonged relative to that obtained for the 5 patients in the present study. The explanation for these findings is difficult, but the lack of uniformity in dialysis and the limited number of patients in the gentamicin study may be partially responsible for the differences seen. An additional important factor is o 7 variation in the patient population studied. It has been reported that

- 27 - the ability of the peritoneum to function effectively as a semipermeable membrane may become compromised with recurrent bouts of peritonitis.

The previous history of the single patient without peritoneal inflammation 81 studied by Smithvas and co-workers, is unknown. In addition, the patients who were studied while having documented peritonitis may have indeed undergone several similar episodes, each possibly resulting in progressively more scarring and fibrosis of the peritoneal membrane.

Therefore, if it is assumed that for "small" solutes (molecular weight

(MW)<. 40,000), such as urea (MW=60), creatinine (MW=113) and the amino¬ glycosides, the major path of transport from the capillaries to the 44a peritoneal fluid is via intercellular channels, then alteration in the size, shape or change of these "functional pores" may reduce permeability 63a

Finally, Bulger, et al reported the variability displayed in peritoneal diffusion of the same antibiotic in different patients. It is concluded that the difference seen between gentamicin and tobramycin as described above, may be secondary to variation in patient population, lack of sufficient sample size and variation in dialysis technique.

The fact that the present study shows tobramycin to be dialyzable is 33 supported by the recent investigation by Gordon and co-workers who studied the serum protein binding of aminoglycosidic agents. The degree to which a drug is protein bound has been shown to influence not only the therapeutic action, but also the pharmacokinetics of that agent. The aminoglycosides

oo are excreted by glomerular filtration, the amount filtered being

F)7 - proportional to the concentration of unbound drug. This is analogous to clearance across the peritoneal membrane. Drugs of high protein binding, such asdoxycycline (protein binding 93%) are poorly removed from the serum in patients undergoing peritoneal dialysis,63 while those of low or

- 28 - > minimal binding such askanamycin*^ are dialyzed quite wel1 . ^

Using ultrafiltration techniques, Gordon, et al, were able to show the protein binding of kanamycin, gentamicin and tobramycin to be essentially zero, while that for streptomycin was found to be 35%.

The values obtained by these studies for kanamycin and streptomycin agree with previous investigations^’^, while those for gentamicin are at variance with the previously reported estimates of 30% gentamicin protein binding.^

That gentamicin is now reported to be minimally protein bound, if at all, is not surprising in view of the several investigations that have compared the clearance of this agent to that of inulin, a substance excreted only by glomerular filtration.^6 The clearances were shown to be almost identical. However, if only 70% of gentamicin in the serum could be considered to be ultrafi1trable, net tubular secretion of the drug would have to be postulated in order to explain the observed data.

Similarly, studies comparing the clearance of tobramycin and inulin*^ obtained comparable results, in addition to showing the lack of probenicid effect. It would appear, therefore, that tubular secretion of these drugs was proposed in an effort to rationalize data that indicated pure glomerular filtration as the mechanism of renal excretion. However, if the protein binding of gentamicin and tobramycin is negligible, as suggested by Gordon, et al ,^3 then no tubular mechanisms need be proposed to explain the observed data, since the drugs are essentially 100% ultrafi1trable.

Finally, comparison of the clearance of tobramycin to that of urea and creatinine should be noted (Table 10). If intercellular channels

- 29 - are considered to be the major path of transport from capillaries to peritoneal fluid,and it is assumed that substances of greater molecular weight will have increased difficulty traversing these channels,it is expected that CtQbra would be less than either Curea or Ccr. The molecular weight of tobramycin is 519 (as the trihydrate) and, as expected, ^ is less than that observed for urea or creatinine, substances of considerably smaller molecular weight. It is concluded from the present study that a substance of minimal (or zero) protein binding and low molecular weight will be dialyzable.

Therefore, the present data, that the clearance and half-life of tobramycin are similar to that of kanamycin, is not surprising. The fact that gentamicin does not display similar behavior may be explained by considerations dealt with earlier.

At the outset, it was stated that tobramycin was a broad-spectrum antibiotic with excellent activity against . Based on the result of the present investigation, recommendations as to the use of this agent in both local and systemic infection can now be made.

(i) Systemic Infection

An optimal dosage schedule requires maintainance of antibiotic levels that are both therapeutic and non-toxic. In formulating such a regimen, it is clear that the volume of distribution must be considered.

As noted earlier, the undergoes considerable variation with alteration in renal function and is increased with severe renal insufficiency. The net result is lower peak serum levels. Of additional importance in dosage considerations is the range of bacterial sensitivity. The anti¬ bacterial spectrum of tobramycin and bacterial sensitivities were outlined

- 30 - in the Introduction and will not be repeated here except to mention the 1 8 report of Bodey, et al , documenting the susceptibility of 457 clinical isolates of gram-negative bacilli at an MIC of 1.56 mcg/ml.

If it is assumed that a peak serum antibiotic level (P^) of 6 mcg/ml results in adequate therapeutic levels, distributed into a volume of approximately 35% BW (compromise between 1- and 2-compartment analysis), then drug dosage can be estimated for this patient population by the following calculations:

= 6 mcg/ml = 35% BW = 25 liters

BW = 70 kg

then

Dosage (mg/kg) = (P^MV^) = (6 x lCT^g/ml) 0.025 x 10+^ml) BW ~ 70~kg

Dosage = 2 mg/kg

When administered every third half-life, this dose of antibiotic will result in the calculated peak serum level, but the usual peak-trough effect will be present. When dealing with a sensitive organism, such variation 15 in serum levels is acceptible. It has been shown by Cutler, et al, that in patients with renal failure a more stable drug level is attainable, with less variation between doses, by administering one-half the loading dose every half-life.

Looking at Table 3, it is seen that there are two estimates of half- life based on the data collected in the present study. Inasmuch as neither value is to be considered absolute, and in order to facilitate drug administration, a half-life of 12 hours will be used in calculating the dose interval. Therefore, the suggested dosage schedule is given as follows

31

Loading Dose - 2 mg/kg

then either

(a) loading dose given every third half-life (36 hours) or (b) one-half the loading dose given every half-life (12 hours)

(ii) Peritonitis

Peritonitis has always been a serious complicating event in the natural history of patients maintained on peritoneal dialysis, and is usually defined as a syndrome comprised of abdominal pain, fever and 41 bacteriologic confirmation of infection.

The present study found levels of tobramycin in the dialysate to range from 0.44 to 1.60 mcg/ml , (See Appendix) with a mean of 0.91 mcg/ml.

Based on in vitro studies presented earlier, these levels would not be bactericidal for many gram-negative organisms. Similar data was presented for gentamicin.

In addition to patient variability, the fact that the dialysis solution if removed before equilibration with the serum is achieved, usually precludes the possibility of therapeutic dialysate concentration being attained. It should be noted, however, that none of the patients in the present study had peritoneal inflammation. It can, therefore, be expected that with peritonitis, some patients may achieve therapeutic 81 levels as evidenced by the data given for gentamicin. However, because of the uncertainty in maintaining adequate peritoneal fluid levels of antibiotic, this problem has long been dealt with by the use of intra- 14 74 peritoneal drug administration. 5 It is recommended that in order to insure adequate dialysate bactericidal activity, tobramycin be added to the peritoneal infusion.

32 -

81 Studies on the intraperitoneal administration of gentamicin in

patients with peritonitis have shown equilibration between dialysate and serum after 12 hours. However, because of the 12 hour delay before 41 sufficient serum levels are achieved, Hyams, et al, administered an

initial 80 mg intramuscular dose followed by 5 mg/liter intraperitoneally.

This regimen resulted in equilibration between serum and peritoneal fluid

in the range 1.5 to 5.0 mcg/ml. When 10 mg/ml were given intraperitoneally, equilibration levels varied from 1.4 to 13.0 mcg/ml. Unlike some antibiotics, such as tetracycline, serum accumulation does not appear to occur with gentamicin even after repeated intraperitoneal administration which suggests that significant extra-renal clearance exists for this agent. Assuming the applicability of the above data to tobramycin disposition, and the present data, it may be concluded that bactericidal serum and dialysate activity can most rapidly be achieved by administering a parenteral loading dose, followed by intraperitoneal administration every 12 hours. Therefore, the suggested dosage schedule for tobramycin

in patients with documented peritonitis is given as follows:

Loading Dose - 2 mg/kg

then

5 mg/liter every 12 hours

Finally, it should be emphasized that the variables and assumptions

in the formulation of these regimens are multiple. Although a plan of therapy is suggested, it is advised that serum and dialysate levels of tobramycin be determined by the assay procedure outlined earlier. Both the speed and the accuracy of this determination make it possible to

monitor body fluid drug levels and thereby allow for patient-to-patient

33 -

variability. This approach yields optimal patient care.

C. Clindamycin

Although there have been no studies reporting the effect of peritoneal

dialysis on clindamycin disposition, data is available for both normal

and impaired renal function. The pharmacokinetics of the parent compound,

lincomycin, have been documented in normals, uremics and in patients

undergoing dialysis.

In the present study, the average peak serum level of antibiotic

for 3 patients studied, was found to be 15.41 mcg/ml in samples obtained

5 minutes after the end of the 20 minute intravenous infusion (Table 8, Fig. 5).

This value is considerably greater than the 8.42 mcg/ml reported by 21 DeHaan. In addition, serum levels obtained in the present study were

uniformly greater than those seen in patients with normal renal function, and were equal to the levels expected after a 1200 mg intravenous dose. 44 This finding is similar to that reported by Joshi and Stein who found serum levels in anephrics after a 300 mg dose to be elevated approximately

2.5 times those seen in normals. Comparing the results of the present study, in which 600 mg of clindamycin was administered intravenously, to the above investigation, the mean peak serum concentrations were observed to be 1.25 times greater with the larger dose. Serum levels of lincomycin anephrics is similar, with peak concentrations being greater 68 than those obtained in normals by a factor of 3.25.

Assay determinations on samples of peritoneal dialysate showed no

antibacterial activity after the initial exchange. The mean dialysate

concentration during the first hour of dialysis was 1.81 mcg/ml. The

present study shows that except for minimal early drug clearance, clindamycin

34 -

is not dialyzable. It is, therefore, expected that this agent is highly

protein bound. Similar conclusions have been reached by Reinarz and 68 McIntosh for lincomycin.

The T-j^0 of intravenously administered clindamycin has been determined 21 95 44 in patients with normal ’ and impaired renal function. The present

study resulted in 3 estimates of T^ (Table 5). When determined by

analysis of the terminal log-linear portion of the serum decay curve,

the mean T-^b for the 3 patients studied was 4.55 hours. When plotted

semilogarithmically, the data for the individual patients revealed that

loss of antibacterial activity for patient #2 was monoexponential, while

patients #1 and 5 showed early non-1inearity implying bi-exponential decay.

Tl/2kel ca^cu^ated Tor the latter two patients was 2.81 hours. Finally,

the half-life determined from the log-linear portion of the average

serum decay curve (Fig. 5) was 6.79 hours.

While the T^ of clindamycin in normals receiving 600 mg intravenously 21 was 4.19 hours (range: 2.49 - 5.64) in the study reported by DeHaan, 44 Joshi and Stein found the half-life in anephrics not on dialysis to be approximately 6 hours. This data indicates prolongation of serum half-life

in patients with severe renal impairment. The present study shows T-j^b

and T-j^kgi approximating that seen in normals.

Looking more closely at the above values (summarized in Table 9),

the methods of T-^ calculation deserve attention. Although the data 44 collected by Joshi and Stein did not yield a straight line when plotted

semi-logarithmically, graphical analysis of the terminal log-linear portion of

the average decay curve of 7 patients was used exclusively in the determination

of the T-j/2 reported. Data from the present study is comparable (6.79 hours)

35 -

when similarly analyzed. These calculations most likely over-estimate

the actual T-^. Cimino, et al reported the half-life of orally

administered clindamycin to be 3.36 hours in patients with end stage

renal disease. The half-life of orally administered drug in normals 95 ranges from 1.50 to 3.54 hours. It is concluded that the half-life

of clindamycin may not be prolonged in the presence of compromised

renal function.

The present study does not permit a firm statement as to drug

disposition in uremia because of small sample size. However, prolonged

T-jin uremics receiving clindamycin might be expected since Reinarz c 68 and Min tosh have shown a similar effect on the disposition of lincomycin,

the chemically similar parent compound. The half-life in anephrics was

found to be approximately 13 hours, while in normals T-j^ = 4.76.

Additionally, peritoneal dialysis was shown to have no effect on serum

T-j/2* Of note is the use of 2-compartment analysis similar to that used

in the present study. Both the larger sample size and the use of the

above model for kinetic analysis make this report reliable. It is to

be expected, therefore, that serum T-^ of clindamycin in anephrics should be similarly prolonged. Further investigation, with larger sample size,

and adequate data analysis is needed. It is concluded from the present

study, however, that peritoneal dialysis has no effect on clindamycin

disposition.

The area under the serum decay curve of clindamycin (Fig. 5) determined

by the trapazoidal rule was 49.88 (mcg/ml)(hour). Similar calculations

for normals receiving an identical initial intravenous dose yielded a 21 value of 35.1. Comparison reveals the total administered dose of

36 clindamycin to be significantly greater in anephrics than in normals.

It was stated earlier that clindamycin is an antibiotic with activity against gram-positive and gram-negative aerobic and anaerobic pathogens. Based on the results of the present investigation, the following recommendation as to the use of this agent in the patient population studied can be made:

In view of the higher peak and mean antibiotic levels achieved in anephric patients, adequate serum concentrations can be attained at a lower administered dose. The present study showed peak serum levels to be approximately 2-fold greater than those achieved in normals. In 44 agreement with Joshi and Stein, it is suggested that the amount of clindamycin administered intravenously to anephrics should be approximately one-half that required to achieve the desired serum level in patients with unimpaired renal function. Peritoneal dialysis does not affect this regimen.

37 -

VI. CONCLUSIONS

A. Tobramycin

1. Peak serum levels of tobramycin in functionally anephric patients were less than expected, probably secondary to larger volume of distribution.

2. Peritoneal dialysis leads to significant clearance of this antibiotic with a resultant reduction in serum half-life.

3. Tobramycin disposition in functionally anephric patients without peritoneal inflammation and undergoing peritoneal dialysis, appears to be similar to the pharmacokinetics of kanamycin.

4. If bactericidal serum levels of tobramycin are to be maintained, it is recommended that a parenteral loading dose be administered, followed by either (i) an identical dose every third half-life, or (ii) one-half the loading dose every half-life. In the presence of peritonitis, it is recommended that a parenteral loading dose be given, followed by intra- peri toneal antibiotic administration every 12 hours.

B. Clindamycin

1. Peak serum levels of clindamycin in functionally anephric patients were approximately 2-fold greater than those expected in normals after an identical parenteral dose. It is, therefore, recommended that the administered dose of this agent be one-half of that required to produce desired peak serum levels in patients without renal impairment.

2. Peritoneal clearance of clindamycin during dialysis was shown to be essentially zero. It is concluded that dialysis does not affect clindamycin disposition in this patient population.

3. Small sample size in the present study did not permit accurate estimation of serum half-life.

38 -

VII. TABLES AND FIGURES

Serum Concentration of Tobramycin Administered to Patients Undergoing Peritoneal Dialysis II on po o O —h PO O 03 “5 sz r+ 03 _i. QJ CO O 2 -S 03 r+ 03 =3 ~Ih in CL in CO sz CD CQ CO —t 3 3 —i. 3 . c+ 3 -h c in _i. 3 *o _i. 03 o in o QJ —1. 3 r+ r+ CD =tfc — ^ ■cs o CO o CO o CO o -o —1 CO o -o cn 1 • cn 00 • CO no —i —i —» • cn cn ro • no -P> ♦ CO -1 PO o PO • . —> PO cn •"j PO • on ''j cn CO • _1 on • —i PO co '-J . '■O CO cn PO —1 . CO on PO • . PO CO -P* . on co CO CO 1 1 1 1 I PO on CO on . • po on PO • • '-j o CO CO o co . -p* CO • CO 1X3 CO • CO on o \l PO . CO CO • on PO . o oo on

Mean ± SE 4.66+1.94 3.29+1.49 2.89+.37 2.21+.20 2.08+.20 1.64+.16

Table 2

Clearance (C) of Tobramycin, Amount of Drug Removed After

12 Hours of Dialysis, and Average Peritoneal Dialysate Concentration

Patient C Amount Removed Dialysate (ml/min) (mg) (mcg/ml)

1 20.01 22.48 0.98

?

3 12.31 17.30 0.79

4 12.73 18,79 0.81

5 14,86 25.43 1 .07

Mean SE 14.98 ± 1.77 21.00 ± 1.83 0.91 ± 0.07

Table 3

Tl/2 Tobramycin (hours)

Patient Tl/2b T1/2kel

1 19.25 10,52

2 16.50 8.90

3 19,25 13.05

4 8.88

5 16.50 10.50

Mean SE 16.08 ±1.90 10.74 ± 0.84

Ti/2 calculated from the terminal log-linear portion of the average serum decay curve (Fig. /1) = 14.44 hours. •'Ml!. . •.■'/llli'MU

1 Table 4

Volume of Distribution of Tobramycin

Patient %BW %BW vd

2 16.07 29.49 15.71 28.83

3 23.29 40.43 23.89 41 .48

4 16.48* 27.93

5 19.88 29.76 19.33 28.94

Mean SE 21 .40± 2. 79 34. 34 ± 3. 30 22.93 ± 3.68 36i.35 ±4.41

*Patient #4 displayed monoexponential serum decay of drug activity.

Table 5

T of Clindamycin (hours) and Concentration of 1/2 Antibiotic in Peritoneal Dialysate (mcg/ml)

Patient T alysate 1 / 2b Tl/2kel 1 5.02 3.73 1.42

2 2.22* — 2.53

5 6.42 1 .89 1.49

Mean SE 4.55 ± 1.23 2 81 ± 0.92 1.81 ± 0.36

T-|/2 calculated from the terminal log-linear portion of the average serum decay curve (Fig. 5) = 6.79 hrs.

*Patient #2 displayed monoexponential serum decay of drug activity.

**Assay for clindamycin was performed on dialysate from exchanges 1, 3, and 6, Only exchange 1 had any detectable antibiotic activity. rim. Table 6

Coefficients and hybrid rate constants for the equation n -at . n -bt y = Ae + Be

Antibiotic: Tobramycin

Pt # A B a b kel

1 1.28 2.11 0.0164 0.0007 0.0011 2 4.32 3.24 0.0101 0.0006 0.0013 3 1.19 2.38 0.0176 0.0006 0.0009

4* — 3.35 0.0013

5 1.84 3.36 0.0134 0.0007 0.0011

Antibiotic: Clindamycin

Pt # 1 4.89 11.70 0.0146 0.0023 0.0017

2* — 12.22 — 0.0052 5 14.37 2.98 0.0124 0.0018 0.0061

*Patients #4 and #2 displayed monoexponential serum decay of drug activity. 'ivt j.lms; .'no:'> vio > i n.!ii l>nr< ,’ 1 iv' i .> i T ] -nO

n r r viMG'rr!oT : o L+o rr 5 11A.

f\ \\ ;H

P o Comparison of known Data on Kanamycin, Gentamicin, and Tobrairiycin Collected in this Study

3 3 0 O -O -i.-o -i.-o CD 3 rt> 3 ro 3 3 -h 3 ~h 3 d» -*• __i __i. —1 -j. —1 d --* ■>. CD d- Qj d* CD O ^ CD cn co CD 3 O 3 O 3 3 CD 3 • • 3 3 3 3 3 3 no 3 ro ro co cn ro o i 1 ro cn cd ro —* —* cd cd ro cd a- —* O XT IQ zr — ■o CO i 1 TD CO n- cd cn 0 cn rr Qj CO rr —* ro ~o CO o —* n> ^i 1 3“ • —1. —1 • • • —* • —• ZZ~ 4* —> it zr • c \ 3 cn TO 3 1 1 3 cn 0 co ro 0 O cn O CL O 3 3 ro T] ~1 —1. 3 CL 3 CL 3 -*• —j. co ii o >_-- s_-- 0 —J. CD O CO co "O CD "O CD -a —• >—<•* ^ -5 —* 3 —• 3 << o O CD << CD C< co CO 00 CO 10 CO CO to —*. -VJ fD —*• CD -i- CD CO .{* 3 VI 3 CO 3 rr d- d

3 ro CO 3 PO i 1 1 1 1 co co ro 1 1 i 1 1 1 —j 1 co cn 0 cn 1 J ro 70 8 i 1 1 1 CO 1 4* 4* co 1 1 3- ro S§ 3 < co a> — a. Table 7

-C* i 1 1 1 1 1 i 1 1 1 1 1 roOM 4* CD 1 VO i 1 1 1 1 1 1 00 i 1 1 1 1 1 4* -P* vo VO CO

CO < < CO Cl CL ro • "O *^J • ^ —* cn —i —i ._s CO i 1 ^ CD 1 i 1 1 1 1 1 i • •

3 O (T) • 0 CD -fc* 3 4* cn II i 1 1 1 1 1 1 O I i 1 1 1 1 1 ro —j 1 1 i 1 1 1 1 • • 1 1 VO —1 i 1 B 1 1 O O 1 i o* i cn o

Table 8

± SE 1.88 0.26 1.00 1.20 1.23 0.98 0.50

l I Summary of Available Clindamycin and Lincomycin Data and Data Collected in this Study fD • ' QJ —„ 33 3 • 7C 3 CO 3 D> QJ fD 3 33 —i c+ —1. 3 o < o • O 33 —1 3 3" 3 cT —i. c+ O 3 QJ O 3 \ 3 -—- §1 CQ fD CQ 30 3“ —) 3 \ '— ro •—• —1 3 o 3 * ! I 1 1 ro —J • -Pi • 03 cn • o o n CO 3 =3 >—i O 2 —1 --s —1 -CO CQ c+ 3 i i i i ro -Pi o • o CD -pi • 3 sc 3 O scl-o SD CO —1 • _i o 3 c+ fD o ->• —r+ CO CO fD O c+ CO • "O 1 1 1 1 -P^ ro CD • ■"j —> cn 33 3 CO • =5 3 O -*• O SC o -P» • CD CO cn co ro .—i • • -Cs. 3 3 3 —i —i I—I O r+ O CO • O 1 1 —- ro CD • cn CD -pi 03 CO CO • "vl 3 I—i "■J 00 • 03 o O < --—*N ' •- -—- CQ sc 3 n c+ CO • -s fD TO r\3 3 3 —i. —1 cx> - CO CO • CTv o O o o 3 I—I Qj < —1 CO r+ — o CQ CL c+ o • CO 4*> • 00 CO —1 cn —i • -Pi o 3 03 CD O -O 3 O o -1- 3 i—i CO < ^ 3 -s N—* CQ TO o -< II -Pi —1 7T CQ ro cn • cn CO —1 —1 no ro fD —1 II —I —1 \ \

*1 hour sample I T3 Q) r+ CO ro X- rD =s r+ =tfc

"O CD cn r\3 cn on on rv> • • • • • o o o o —1 CO VQ on -P* -Pi -p> CD co vo o cn • • • CTi • X- o o o • o o fD o —1. CD CD 33 .-1 ro _1 —.1 —i << 1 + —i CD VO cn rv> in • • • • • CD oo ro on ro CO co • • O co —I —1 VO CD r+ ~S fD o CD o c+ -h —1 IV) -h _1 CD fD fD • O ro on i o 33 CD Z3 “h —i oo oo on j CO -CD Q. “O O • fD -5 ro CD -s co "O fD r+ CD CD O c+ ~S =3 —i. CD fD fD ZS CD 33 o c+ ro fD oo O =tfc • IV) VO CD CD • VO ro ro ro i ro oo -1^ oo i oo o XT CD 1+ • • • i • 3 -5 O t/) O' OO on •-o i 00 o —1 O j CO fD -5 O fD 33 O CD 00 fD o -5 -5 fD CD c+ fD < fD 33 VO fD V/> _, 3 co _, _, 1 ro —1 o -Pi ro ro 1 o \ r+ CD o 1+ • • • 1 • 3 O 33 -pi. \i co 1 o Cr cx —1 cn oo —1 1 —> o -5 —- CD -5 "O o fD cr CD -s CD CD 33 << Q- o

O CD X C r+ CJ1 CTi cn -P* CO —1 -5 O co o o o O fD cr O CD -5 1 + CD vo

CD vo x a O VO vo VO —> -s -$ cn co cn O fD 1+ O CD

-P> O CD X CD c+ Cn cn cn cn co —1 “S O CO -p= IV) ro -p> O CT O -5 ■ + CD

00

Table 11

Comparative Mean Clearance Values of Urea and Creatinine (ml/min)

Patients # pts C C C /C urea cr cr' urea tCRF 8 *17.1 ± 0.84 13.0 ± 0.88 0.77 ± 0.04 (publ ished)

CRF 4 26.82 ± 1.28 23.99 ± 0.17 0.91 ± 0.04 (present study)

*Mean ± SE tChronic renal failure rz i c*n Figure

o o f-

o o CD

o o in

o o 'i-

o o rO

O TIME (minutes post infusion) O CJ

O O

(iuj/6rt) NiDAWvaaoi do NouvaiNdONOD wnads

LO

s- 13 CT>

(Iiu/Orf) NIOAWVQNnO JO NOLLVHXN30NOO WOddS

VIII. APPENDIX

Clearance (C) of Urea and Creatinine over 12 Hours of Peritoneal Dialysis -5 03 CD fD 33 CD O CD ~o CD c+ r+ =3 CD (D c+ —1. 33 fD o _1 c 3 CD -5 CD —r. m X n or CD =3 CD UD 3 3 —1. Z5 -—-V v—■ CQ ro IV) 45a • ro ro —i CO o 00 • oo ro cn a O ro O 00 • o ro ^4 —i ro ro • ro ro o co co -P> O CD -pa • ro ro ro O O —' IV) CT) —i —i cn co —i cn 45a ro co X- ro ro • —i CD ro cn cn • 00 -Pa CO ro o • cn o 45a • 00 ro o cn o ro CT) ro co • CJ1 • oo 45a CT) cn -Pa cn ro on _1 -|5a o ro • CT) CO ro rv> ro ro co -1 CTI 45a o o CO CT) CD 45a cd cn cn ro cd X- X- i ro i ro 1 co i cn I O 00 1 CD —1 1 • 1 45a 4^a i ro ro I 45= -pa i o ro 1 CO CD 1 o o IV) O') ro cn • —i cn no • ro 45a O o e ro ro o o —1 Co or cn ro ro O -pa • • cn ro 4=> co iv) iv) ro CO -P> Cn —' ro cd CO -Pa -Pa no rv> o O 00 CO CO • ro cn cn

*Dialysate not collected for patient #2. ^^Approximately 5litersof dialysate accumulated in the peritoneal cavity of patient #4. Determinations were not made on dialysate from this exchange.

BUN and Creatinine During 12 Hours of Peritoneal Dialysis

Patient# Serum Time BUN cr (hrs. post-infusion) (mg%) (mg*)

1 ^control 62 12.8 1.5 62 12.9 6.5 51 11.0 12.5 46 10.9

2 control 129 15.3 1.5 127 13.7 6.5 117 13.2 12.5 106 13.1

3 control 65 9.2 1.5 65 8.8 6.5 55 8.0 12.5 49 7.4

4 control 67 16.5 1.5 69 16.5 6.5 58 14.4 12.5 48 13.1

5 control 75 21.2 1 .5 74 20.2 6.5 65 16.8 12.5 56 16.8

^Control sample taken prior to administration of antibiotic.

Antibiotic: Tobramycin

Serum Assay (mcg/ml)

Patient #1 J.R.

T ime Plate I Plate II Mean SD (min post infusion) 5 3.26 3.31 3.29 0.04 70 2.38 2.44 2.41 0.04 130 2.03 2.19 2.11 0.11 370 1.55 1 .74 1.65 0.13 430 1.45 1.71 1.58 0.18 730 1 .29 1.32 1.31 0.02

Dialysate Assay (mg/ml)

Exchange Plate I Plate II Mean SD Exchange Amount C Volume Removed (ml) (mg) (ml/min) 1 1.61 1 .31 1 .46 0.21 2130 3.11 21.51 2 1.21 1 .17 1 .10 0.03 2100 2.50 19.75 3 1.15 1.05 1 .10 0.07 2050 2.48 21.31 4 1.10 1.03 1 .07 0.05 2440 2.51 23.39 5 0.98 0.94 0.96 0.03 1940 1 .86 17.51 6 0.83 0.86 0.85 0.02 2120 1.80 18.20 7 0.82 0.77 0.80 0.04 2210 1.77 18.65 12 0.47 0.41 0.44 0.04 2120 0.97 11.87

Mean 0.98 2.14

Antibiotic: Tobramycin Serum Assay (mcg/ml)

Patient #2 T.M.

T ime Plate I Plate II Mean SD (min post infusion) 5 7.39 7.32 7.36 0.05 70 4.39 5.45 5.19 0.37 130 4.40 4.03 4.21 0.26 370 2.45 2.88 2.67 0.30 430 2.35 2.78 2.57 0.31 730 2.18 2.02 2.10 0.11

Dialysate assay was not performed for patient #2 ) . ! ;• Antibiotic: Tobramycin

Serum Assay (mcg/ml)

Patient #3 R.W.

T ime Plate I Plate II Mean SD (min post infusion) 5 3.33 3.61 3.47 0.20 70 2.79 2.56 2.68 0.16 130 2.21 2.37 2.29 0.11 370 2.03 1.89 1 .96 0.10 430 1 .91 1 .91 1 .91 0.00 730 1.67 1.46 1.57 0.11

Dialysate Assay (mcg/ml)

Exchange Plate I Plate II Mean SD Exchange Amount C Volume Removed (ml) (mg) (ml/min) 1 1.15 1 .24 1 .20 0.06 2475 2.97 18.47 2 0.87 0.99 0.93 0.08 2350 2.19 15.91 3 0.76 0.83 0.80 0.05 2060 1 .65 12.50 4 0.77 0.87 0.82 0.07 860 0.71 5.58 5 0.77 0.79 0.72 0.10 1640 1 .18 9.64 6 0.65 0.68 0.68 0.01 2050 1 .39 11.85 7 0.67 0.64 0.65 0.01 2150 1 .40 12.19 12 0.55 0.54 0.55 0.01 1840 1 .01 10.74

Mean 0.79 1 .56 V-m

v\ II aid I a i c 1*1

3..II (M I fill I l\ ' ' I' 0'-' . I

. > '■ > *i n - ')

Of- I rv p VI ':

n r c:"i i» r* n ;.;i ii

'■ i * i n 11

11 ii ri p 11 '■i'

CiV n ,,...11 Antibiotic: Tobramycin

Serum Assay (mcg/ml)

Patient #4 J.J.

Time Plate I Plate II Mean SD (min post infusion) 5 2.93 3.22 3.08 0.21 70 2.68 2.84 2.76 0.11 130 2.07 2.11 2.09 0.03 370 1.98 1.94 1.96 0.03 430 1.38 1 .14 1 .26 0.17 730 0.97 1 .01 0.99 0.03

Dialysate Assay (mcg/ml)

Exchange Plate I Plate II Mean SD Exchange Amount C Volume Removed (ml) (mg) (ml/min) 1 1.29 1.34 1.32 0.04 2290 3.02 16.36 2 1.01 1.15 1.08 0.10 2345 2.53 15.29 3 0.86 0.88 0.87 0.01 1950 1.70 10.81 4 0.71 0.84 0.78 0.09 2170 1 .69 11.64 5 0.82 0.83 0.83 0.01 2715 2.25 16.74 6 0.71 0.77 0.74 0.04 2080 1.54 12.27 7 0.61 0.66 0.64 0.04 1090 0.70 6.03 12 0.22 0.24 0.23 0.01 5903 1 .36 17.96

Mean 0.81 1 .85 n ■ :\ -’r. y 1K'" >: .V

\' ' > v:-*

V a.: > '

f

f>

'\

:\f

-:nr U I ’•‘ft •

I ' I- : i •: \ ; i

: < t C s

\ i ' ■ ( C Antibiotic: Tobramycin

Serum Assay (mcg/ml)

Patient #5 J.T.

Time Plate I Plate II Mean SD (min post infusion) 5 4.12 4.91 4.52 0.56 70 3.22 2.94 3.08 0.20 130 3.17 2.97 3.07 0.14 370 2.84 2.41 2.62 0.29 430 2.60 2.17 2.39 0.30 730 2.00 1 .96 1 .98 0.03

Dialysate Assay (mcg/ml)

Exchange Plate I Plate II Mean SD Exchange Amount C Volume Removed (ml) (mg) (ml/min) 1 1.47 1.72 1.60 0.18 2400 3.84 20.78 2 1 .16 1.30 1.23 0.10 2360 2.80 15.76 3 0.93 0.97 0.95 0.03 2000 1 .00 10.81 4 0.51 0.46 0.49 0.04 2050 2.49 5.98 5 1.38 1 .39 1 .39 0.01 2150 2.99 18.59 6 1.10 1 .09 1 .10 0.01 2200 2.42 15.39 7 1.09 1 .08 1 .09 0.01 1820 1.98 16.70 12 0.73 0.70 0.72 0.02 2050 1 .48 22.57

Mean 1 .07 2.31 • ,•' -i r,T.

\

1

i

i >

r. ! +1 t•....

-:f \

'.r, . \

r n ' <. . -

"> 1 r ■ ■' r : r. r ( r ■ ■■. r Antibiotic: Clindamycin

Serum Assay (mcg/ml)

Time Plate I Plate II Mean SD (min post infusion)

Patient #1 J.R. 5 15.61 15.66 15.64 0.04

30 — 70 12.20 12.00 12.10 0.14 160 8.67 8.40 8.54 0.19 340 4.70 5.32 5.01 0.44 520 3.85 3.72 3,79 0.09 700 2.50 2.65 2.58 0.11

Patient #2 T.M. 5 13.62 13.96 13.78 0.25 30 11.28 11 .50 11.39 0.16 70 9.34 9.16 9.25 0.13 160 5.65 5.59 5.62 0.04 340 1.48 1 .57 1 .53 0.06 520 0.68 0.69 0.69 0.01 700 0.64 0.67 0.66 0.02

Patient #5 J.T. 5 17.00 16.63 16.82 0.26 30 12.28 11.78 12.03 0.35 70 9.17 8.73 8.95 0.31 160 4.31 4.64 4.48 0.23 340 1 .52 1 .50 1.51 0.01 520 1 .05 1 .11 1.08 0.04 700 0.99 0.89 0.94 0.07

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Description of Project: We would like to ask you to participate in a study involving the use of a new antibiotic Clindamycin/Tobramycin in people who need peritoneal dialysis. The purpose of the investigation is to measure the amount of antibiotic in your bloodstream while you are receiving peritoneal dialysis in the hospital. Ordinarily antibiotics are used to treat . Since you have no infection administration of this antibiotic will be of no value to you. The purpose of this study is to obtain information which could be of importance to others requiring dialysis who do have infections. You are free to refuse to participate in this study or to withdraw from the study at any time. Your refusal or withdrawal will not affect your future care at this institution.

Authorization: I have read the above and agree to the participation of

(name or names and how related) in the project described above. Its general purposes, potential benefits, and possible hazards and inconveniences have been explained to my satisfaction.

Signature

Date

(Physician)

BIBLIOGRAPHY

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41. Hyams PJ, Smithvas T, Matalon R, Katz L, Simberkoff MS, Rahal JJ, dr.: The use of gentamicin in peritoneal dialysis. II. Microbiologic and clinical results. J Infect Dis 124 (Suppl.): s84, 1971.

42. Hyams PJ, Simberkoff MS, Rahal JJ, Jr.: In vitro bactericidal effectiveness of four aminoglycoside antibiotics. Antimicrob Ag Chemother _3:87, 1973.

43. Jackson GG: Gentamicin. Practitioner 198:855, 1967.

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45. Kislak JW: The susceptibility of Bacteroides fragilis to 24 antibiotics. J Infect Dis 125:295, 1972.

46. Klotz AP, Palmer WL, Kirsner TB: Aureomycin proctitis and colitis: A report of 5 cases. Gastroenterol 25>:44, 1953.

47. Koch DF, Rhoades JA: Structure of nebramycin factor 6, a new aminoglycoside antibiotic. Antimicrob Ag Chemother 309, 1970.

48. Kunin CM: Antibiotic usage in patients with renal impairment. Hosp Pract 141 , 1972.

49. Levison ME, Bran JL, Ries K: Treatment of anaerobic bacterial infections with clindamycin-2-phosphate. Antimicrob Ag Chemother 1:276, 1974.

50. Lockwood WR, Bower JD: Tobramycin and gentamicin concentrations in the serum of normal and anephric patients. Antimicrob Ag Chemother 1:125, 1973.

51. McGehee RF, Jr, Smith CB, Wilcox C, Findand M: Comparative studies of antibacterial activity in vitro, and absorption and excretion of lincomycin and clindamycin. Am J Med Sci 256:279, 1968.

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54. Magerlein BJ, Birkenmeyer, RD, Kagen F: Chemical modification of lincomycin. Antimicrob Ag Chemother 1:727, 1967

55. Meyer RD, Young LS, Armstrong D: Tobramycin (Nebramycin factor 6): In vitro activity against Pseudomonas aeruginosa. Appl Microbiol 22:1147, 1971.

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68. Reinarz JA, McIntosh DA: Lincomycin excretion in patients with normal renal function, severe azotemia, and with hemodialysis and peritoneal dialysis. Antimicrob Ag Chemother 232, 1965.

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during peritoneal dialysis. Antimicrob Ag Chemother 1:432, 1973.

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100. Wick WE, Welles JS: Nebramycin, a new broad-spectrum antibiotic complex. IV. In vitro and in vivo laboratory evaluation. Antimicrob Ag Chemother 341 , 1967.

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Unpublished theses submitted for the Master's and Doctor’s degrees and deposited in the Yale Medical Library are to be used only with due regard to the rights of the authors. Bibliographical references may be noted, but passages must not be copied without permission of the authors, and without proper credit being given in subsequent written or published work.

This thesis by has been used by the following persons, whose signatures attest their acceptance of the above restrictions.

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