THE KURUME MEDICAL JOURNAL Vol.27, P.275-298, 1980

THE PHARMACOKINETIC STUDIES OF CEPHALOTHIN, AND CEFMETAZOLE IN THE NEONATES AND THE PREMATURE BABIES

YASUTAKA SAKATA Department of Pediatrics, Kurume University School of Medicine, Kurume, 830, Japan

Peceived for publication November 17, 1980

The pharmacokinetic study of provides essential information for the rational therapy of infections in children and especially in neonates. It is therfore necessary to establish techniques to measure the plasma concentrations of antibiotics, using small volumes. Preliminary studies in rabbits and the further studies in the neonates and in older children showed excellent correlation between the concentration of plasma antibiotics in venous and capillary blood, as measured by High Pres- sure Liquid Chromatography (HPLC) and by the bioassay. We confirmed that the HPLC is more useful for assays, in neonates and children for the following reasons; the volume of the plasma is less than standard bioassay (50 ,milvs 200 l); less time is required (20 min vs 18-20 hrs) ; the method can detect the metabolites; multiple antibiotics can be assayed simultaneously. Pharmacokinetic studies for cephalothin (CET), cef azolin and cef metazole in neonates (2-21 days) and in older children (9-12 years) using bioassay and HPLC showed that these antibiotics had more prolonged half-lives and delayed urinary excretion in neonates than in older children. Desacetylcephalothin (DACET), the metabolite of CET, was detected in both plasma and urine in neonates as well as in older children. The amount of urinary DACET, however, was larger in neonates than in older children, and the half-life of DACET was longer in neonates than in older children.

INTRODUCTION tics : bioassay, gaschromatography (Least et al., 1977), high-pressure liquid chro- Monitoring blood levels of antibiotics matography (HPLC) (Nilsson-Ehle, is a cornerstone to the scientific study I. 1977), -immunoassay (Minshew of antimicrobial therapy. et al., 1975) and radio-immunoassay Neonates have been characterized as (Stevens et al., 1975). "th erapeutic orphans" (Shirkey, 1980) The purposes of this study are to because so little is known about the evaluate the usefulness of HPLC compared pharmacokinetics and safety of antibio- with the bioassay, and to know the tics in this age group. Measuring blood pharmacokinetics of Cephalothin (CET), levels of antibiotics accurately and Cefazolin (CEZ) and Cefinetazole (CMZ) rapidly with small volumes of blood is in neonates and older children. an important first step in understand- Preliminary studies using rabbits ing pharmacokinetics in neonates. were done to answer the following Several methods have been developed questions: 1) is there a good correla- for measuring blood levels of antibio- tion between the blood concentrations

275 276 SAKATA

of the antibiotics measured by HPLC tion at 3, 000 rpm for 15 min. and bioassay? 2) is quantification pos- Bioassay (Microbiological assay) sible using small volumes of blood? Bacillus subtilis ATCC 6633 (Kitazato and 3) is there any difference in the Co., 10•¬9 spores/ml) was used as the test concentrations of antibiotics between organism in all experiments except for venous blood and capillary vessel blood ? assay of CMZ. A 1-ml portion of the In the present study, we employed suspension of the test organism was bioassay to investigate the pharmaco- mixed with 99 ml of melted Antibiotics kinetics of CET, CEZ and CMZ in neo- medium No. 2 (Difco, Co.) at 50•Ž. Ten nates and old children. Blood and urinary ml aliquots of the spore suspension concentrations of CET were also meas- were poured into petri dishes (100•~15 ured by HPLC. mm, Terumo Co. ). Employing the agar well method, four equally spaced pe- ripheral wells were bored (6 mm in diameter) and then aspirated. Aliquots MATERIALS AND METHODS (25 /ƒÊl) of the samples were dispensed into each well. The dispensed sample Preliminary animal experiments disc plates (8 mm in diameter, thin, Six rabbits (body weight 2.8-3.2 kg) Toyo disc) were allowed to diffuse for were given a single intravenous injec- 60 min. at 4•Ž before incubation over- tion (40 mg/kg of body weight) of an night at 37•Ž. Heart infusion agar aqueous solution of sodium cephalothin (Eiken Co.) with 1 % of Micrococcus (Keflin, Shionogi Co. ). Blood samples luteus (109 cells/ml) was used to assay were taken from both auricular veins plasma levels of CMZ. Standard curves and capillary vessels simultaneously of were obtained with CET, CEZ, (Fujisawa each ear, one sample with heparinized Co.) and CMZ (Sankyo Co.) and pre- syringe and a second sample with mi- pared human serum (Moni-trol 1, Dade cro-glass-capillary treated with hepa- Co.) was used to make final antibiotic rin-lithium (Terumo Co. ). Specimens concentrations of 10, 5, 2. 5, 1. 25, 0.63 were stored at -80•Ž after centrifuga- and 0. 32 i g/ml. Pooled rabbits' plasma,

Fig. 1. Bioassay of antibiotics 1 : Cylinder method 2 : Paper disc method 3 : Agar-well method THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 277

however, was used to prepare serial body weight; 1,924-2,826 g) and three concentrations to assay CET in rabbits' children (age; 9.9-11.10 years, body

plasmas. (Fig. 1) weight; 25-31 kg) were administered in a dose of 20 mg/kg. Sample preparation for HPLC and 2. CEZ group: 6 premature babies analysis by HPLC (age; 2-12 days, body weight; 1,400- Chromatography was carried out on 2,030 g) were injected in a dose of 25 a Shimazu model LC-3 A liquid chro- mg/kg. Three children (age; 9.7-12.0 matograph (Shimazu Co.) equipped with years, body weight; 26.0-34.0 kg) were an ultraviolet detector monitoring ab- given in a dose of 20 mg/kg. sorbance at 254 nm, and the absorbance 3. CMZ group: 5 neonates including was recorded with full scale of 0.04 to 4 premature babies (age; 3-16 days, 0.08 absorbance units. A 15 cm•~4.6 mm body weight 2, 200-3, 400 g) and three stainless steel column packed with Zor children (age; 9.1-10.7 years, body Bax ODS (Shimazu Co. ), was used. The weight 20.2-30.0 kg) were administered mobile phase consisted of 40% metha- in a dose of 25 mg/kg. nol in 0.2% aqueous ammonium ace- Blood samples were obtained as fol- tate. Flow rate was maintained at 1.0 lows: 15, 30, 60 min., 2, 4, 6 and 8 hours ml/min. Standard solutions were pre- after injection of CET in neonates, 30,

pared by diluting cephalothin sodium 60 min., 2, 4, 6 and 12 hours after ad- (942 pg/mg of CET activity, Shionogi ministration of CEZ in neonates, and 15, Co.) and desacetylcephalothin (DACET Lot No. 11, Shionogi Co.) to give 1 mg /ml. Samples diluted three-times by methanol were centrifuged at 2, 000 rpm for 10 min. after mixing sufficiently. Ten mil of the supernatants were fil- tered through membrane filtration (0.45 gym, Millipore Co. ), and then injected into the apparatus. Human urine samples were diluted appropriately with 0.1% phosphate buffer and cen- trifuged at 3, 000 rpm for 15 min. The supernatants were similarly filtered and injected.

Pharmacokinetic studies The following studies involving hu man were all done with informed con- sent of parents of the neonates and children. Male neonates including premature babies and children were studied to obtain pharmacokinetic data of CET, CEZ and CMZ. The antibiotics were all given intravenously. 1. CET group: 6 neonates including Fig. 2. Standard 5 premature babies (age; 3-21 days, 278 SAKATA

30, 60 min., 2, 4 and 6 hours after ad- mined by the cylinder method were ministration of CMZ in neonates and of correlated with those obtained by the three drugs in older children. Samples disc and agar-well methods. The of neonates were obtained by healstick correlation coefficient between the technique employing microtainers (Bec- values obtained by the cylinder and the ton-Dickinson Co.) treated with cyricon disc methods is 0.983 and that between or micro-glass-capillaries treated with the cylinder and the agar-well methods heparin-lithium. Urine specimens were is 0.978 (Fig. 3). The correlations be- collected every 2 hours; 0-2, 2-4, 4-6 tween venous plasma and capillary and 6-8 hours, in the groups of CET plasma concentrations were studied and CMZ and 0-6, 6-12 in the group of using the disc method or agar-well CEZ with sterile urine-packes in neo- method. The correlation coefficients nates. between venous and capillary blood concentrations are 0.978 for the disc method and 0.953 for the agar-well method (Fig. 4). The determination of RESULTS the concentration in blood can be there- Core reliably performed using capillary 1. Correlation of the data in three blood. bioassay methods Six rabbits were administerted 40 2. Correlation between the bioassay and mg/kg doses of CET intravenously in the HPLC method order to assay plasma concentrations For venous blood speciments, the by bioassay and HPLC. Concentrations correlation coefficient for the concen- of CET in venous plasma specimens trations measured by the cylinder obtained after administration as deter- method and by HPLC is 0.934, and that

Fig. 3. Correlation between venous plasma concentrations as determined by cylinder method and paper disc method or agar-well method THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 279

Fig. 4. Correlation between venous plasma and capillary plasma concentrations by paper disc method or agar-well method

Correlation between venous plasma Correlation between venous plasma concentrations by HPLC and cylin- and capillary plasma concentrations der method by HPLC

HPLC (Venous plasma)

Fig. 5. 280 SAKATA for venous plasma and capillary plasma and that is 0.986 when agar-well meth- concentrations by HPLC is 0.945 (Fig. od and HPLC were compared (Fig. 6). 5). The coefficient is 0.990 when the Thus, quantification of the concentra- disc method and HPLC were compared tion was possible with capillary blood with each other, using capillary blood by HPLC.

Fig. 6. Correlation between capillary plasma concentrations by HPLC and paper disc method or agar well method

TABLE 1 Plasma levels of Cephalothin in neonates

N. D.: Not detected, Bioassay THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 281

3. Pharmacokinetics of antibiotics in neonates and older children (1) CET a) Plasma concentrations Concerning the plasma concentra- tions of CET by bioassay at first, the mean peak value in neonates was 60.7 11.6 ,cog/ml and the range was 48.6 to 78.0 ƒÊg/ml at 15 min. after injection. The mean plasma level at 6 hours after the administration was 3.6 ,ug/ml and gradually decreased to 2.0 1ƒÊg/ml at 8 hours. The mean half-life was 1.47•}0.44 hour and the range was 0.94 to 2.06 hour, which showed the half-life tended to be longer in the younger neonates (Table 1, Fig. 7). In older children, the mean peak value was 60.7•}3.8 ,ƒÊg/ml at 15 min. as in neonates, and rapidly decreased to 1.0 ƒÊg/ml at 2 hours after injection. The plasma CET was not detectable at 4 hours. The mean half- life of CET in older children was 0.31 hour, about one-fifth of that in neo- Fig. 7. Plasma levels of Cephalothin nates (Table 2). (Intravenously) The same samples were used to meas- ure the plasma concentration of CET reached the maximum after 30 min. in and DACET by HPLC. The mean peak three patients, 15 min. in two patients level of CET was 33.2 ,ƒÊg/ml after 15 and 60 min. in one patient. Chronological min. and gradually decreased to 0.3 ,ƒÊg/ changes of the DACET/CET ratio were ml at 8 hours. The mean half-life was 0.21 at 15 min., 0.27 at 30 min. and 1.18 •} 0.42 and the range was 0.79-1. 50 0.31 at 60 min. after injection (Table hour. The plasma DACET concentrations 3, Fig. 8). In older children, the mean

TABLE 2 Plasma levels of Cephalothin in children

N. D.: Not detected, Bioassay TABLE 3 Plasma levels of Cephalothin and iDesacetylcphalothn in neonates

N. D.: Not detected, HPLC THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 283

peak value of CET was 46.4•}3.3 ,ƒÊg/ml at 15 min. after injection and ranged 42.8-49.3 ,ƒÊg/ml. The mean half-life was 0.20 •} 0.02 hour. The plasma DACET levels reached the maximum levels after 15 min. in two patients and 30 min. in one patients. The plasma CET concen- trations measured by HPLC seemed to be lower compared to those by bioassay, even if bacteriocidal activity of DACET (about one-sixth of CET) is considered. The DACET/CET ratios at 15 min., 30

min., 60 min. and 120 min. were 0.12, , 0. 30, 0.25 and not detection, respec- tively. This result suggests that DACET disappeared from blood faster in older children than in the neonates (Table 4). b) Urinary concentrations and re- covery rates At first, urinary concentrations were assayed by bioassay. Urinary CET levels in three day old and six day old neonates were maximum between 2-4 hours after the administration of the drug. These levels were 871 ,ƒÊg/ml, 2,539 ƒÊg/ml, Fig. 8. Plasma levels of Cephalothin and respectively. In the other four neonates, Desacetylcephalothin (Intravenously) maximum levels were reached in 0-2 hours after injection. The mean peak

TABLE 4 Plasma levels of Cephalothin and Desacetylcephalothin in children

N. D.: Not detected, HPLC 284 SAKATA

TABLE 5 Urinary excretions of Cephalothin in neonates

level was 968•}654 ,ag/ml and the range was 436 to 2,254 ,ƒÊg/ml in 0-2 hours. The mean urinary recovery rate in 8 hours after the administration was 58.4%

, including 29. 1% in the three day old neonate (Table 5, Fig. 9). On the other hand, in older children, urinary CET levels reached the peak level in 0-2 hours after the administration. The mean maximum values of urinary concentrations and recovery rate were 6,815 ,ƒÊg/ml and 71.8%. The mean re- covery rate at 6 hours was 73. 1%. The mean recovery rate in older children was higher than in neonates (Table 6).

Urinary concentrations were also determined y HPLC. Urinary CET levels in the three day old and six day old neonates were at their maximum Fig. 9. Urinary excretions of Cephalothin between 2-4 hours after the adminis- THE PHAR,MACOKINETIC STUDIES OF ANTIBIOTICS 285

TABLE 6 Urinary excretions of Cephalothin in children

tration of the drug as well as results with low body weight had the highest by bioassay, these values were 471 and value of the total rate of urinary re- 1,620 ,ƒÊg/ml. In the other four patients, covery in the 8 hour period. The mean the levels between 0-2 hours were rate of urinary recovery accumulated maximum with mean level of 839 ,ƒÊg/ml. in 8 hour period was 55.2±14. 7%, which The values showed a remarkable de- exceeded that of CET (Table 7, Fig. 10). crease over the next two hour period, In older children, the mean peak value with mean levels in 4-6 hour period of of urinary CET concentration was 88 ,ƒÊg/ml and 6-8 hour period of 33 ,ƒÊg/ml. 5,724±3,758 ,hg/ml and the range was The mean urinary recovery rate of CET 1,389 to 8, 056 ,cog/ml in 0-2 hours. Dur- in 6 hours was 36.7% and in 8 hours ing the next 2 hour period, the mean was 37.9%, including the minimum value declined precipitously to 79 ,cog/ rate of 15.1% in the three day old ml; it was not detectable during the neonate. The DACET concentrations in last 2 hour period. During the first urine specimens reached the maximum two hours, 65.2% of CET administered between 2-4 hours in the 19 day old was recovered, and overall recovery neonate and in the two babies whose rate in the 6 hour period was 66.0%. urinary levels of CET were maximum This was 1.78 times higher than that in the same period. These values ranged in neonates. The DACET concentration from 824 ,ƒÊg/ml to 2,056 ,ƒÊg/ml. The in urine also showed the mean maximum levels between 0-2 hours in the other value was 2,007•}1,376 ,ƒÊg/ml and the three neonates were 469-760 ,ƒÊg/ml. The range was 424 to 2,907ƒÊg/ml in the maximum of mean DACET level in urine initial 2 hours and overall recovery rate specimens of six patients was 865 ƒÊg/ml in the 6 hour period was 25.4% . The between 2-4 hours. The other mean total recovery rate of CET and DACET

DACET levels between 0-2 , 4-6 and was 91.4% . These values closely re- 6-8 hours were 477, 276 and 207 ,ƒÊg/ml, semble those obtained by bioassay, if respectively. The 19 day old neonate bacteriocidal activity of DACET is TABLE 7 Urinary excretions o Cephalothin and Desacetylcephalothin in neonates

N. D.: Not detected, HPLC THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 287

Fig. 10. Urinary excretions of Cephalothin and Desacetylcephalothin in neonates

TABLE 8 Urinary excretions of Cephalothin and Desacetylcephalothin in children

N. D.: Not detected, HPLC 288 SAKATA considered (Table 8, Fig. 11). the three day old neonate and the nine The results of plasma and urine year old child by HPLC are shown in concentrations of CET and DACET in Fig. 12, 13, 14 and 15.

Fig. 11. Urinary excretions of Cephalothin and Desacetylcephalothin in children

Fig. 12. Plasma concentrations of Cephalothin and Desacetylcephalothin in the newborn, 20 mg/kg i. v. (3 day old neonate, male, weight 2,278 g, low-birth-weight infant) 0.08 AUFS THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 289

Fig. 13. Plasma concentrations of Cephalothin and Desacetylcephalothin in the child, 20 mg/kg i. v. (9y. 9m., male, weight 25 kg) 0.08 AUFS

Fig. 14. Urinary concentrations of Cephalothin and Desacetylcephalothin in the newborn, 20 mg/kg i. v. (3 day old neonate, male, weight 2,278 g, low-birth-weight infant) 0.08 AUFS 290 SAKATA

Fig. 15. Urinary concentrations of Cephalothin and Desacetylcephalothin in the child, 20 mg/kg i. v. (9y. 9m., male, weight 25 kg) 0.08 AUFS

TABLE 9 Plasma levels of Cefazolin in neonates

Bioassay THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 291

(2) CEZ a) Plasma concentrations Blood CEZ concentrations were studied in 6 neonates by means of bioassay only. The CEZ concentrations showed a mean maximum value of 91.8 ,ƒÊg/ml with a range of 61.7 to 123 ,ƒÊg/ml a t 30 min. ; in the second and the fifth neonates, the values at 30 and 60 min. were identical. At 12 hours, the mean value was 12.4•} 5.5 ,ƒÊg/ml and the range was 4.1 to 17.5 ,ƒÊg/ml. The mean half-life was 4.05•}0.72 hours and the range was 2.80 to 4.74 hours, which is 2.8 times longer than that obtained for CET by bioassay (Table 9, Fig. 16). In older children, the plasma concen- trations showed a mean peak value of 122.9•}9.5 ,ƒÊg/ml with a range of 115.2 - 133.5 ,ƒÊg/ml at 15 min. At 6 hours the mean concentration was 1.6 ,ƒÊg/ml; in one patient the concentration was not Fig. 16. Plasma levels of Cefazolin detectable. The mean half-life was 0.95 (Intravenously) hour, which is approximately 1/4 of that in neonates and 3.2 times of that of CET in older children (Table 10). in the cumulative 12 hour period. These b) Urinary concentrations and re- values are somewhat less than those covery rates for CET, although the initial doses of In neonates, a mean recovery rate CEZ was higher (Table 11, Fig. 17). In was 36.2•}12.5% and the range was older children, the mean peak value 21.4-56.8% in the initial 6 hours. A was 3,099•}1,788 ,ƒÊg/ml and the range mean of 44.9% of the drug appeared was 1,049 to 4,337 ƒÊg/ml during the

TABLE 10 Plasma levels of cefazolin in children

N. D.: Not detected, Bioassay 292 SAKATA

TABLE 11 Urinary excretions of Cefazolin in neonates

initial 2 hour period. The mean recov- ery rate during the same period was 56.6 %, which exceeded that in the 6 hour period in neonates. In the cumu- lative 6 hour period, 71.6% of the drug was excreted, which is similar to that of CET in older children (Table 12).

(3) CMZ a) Plasma concentrations The CMZ concentrations in plasma and urine were also determined by bioassay only. In neonates,the mean maximum value was 34.1•}4.8 ,ƒÊg/ml and the range was 26.0 to 36.5 ƒÊg/ml at 15 min. This mean value is approximately 1/3 the value for CEZ at 30 min. after injection of the same dose, and it declined gradually to reach the mean value of 4.8 ƒÊg/ml with arange of 4. 1 to 7.6 ,ƒÊg/ml at 6 hours. The mean half-life was 1.75•}0.46 hour Fig. 17. Urinary excretions of Cefazolin and the range was 1.08 -2. 16 hours, which is somewhat longer than that of CET and about 1/2 that of CEZ (Table 13, 0.05 hour and the range was 1.01-1.10 Fig. 18). In older children, the maximum hour, which is shorter by 0,69 hour value was also found at 15 min. The than that in neonates (Table 14). mean peak value was 194.2•} 13.8 ,ƒÊg/ml b) Urinary concentrations and re- and the range was 180 to 207.5 ,ƒÊg/ml, covery rates which is about 5.7 times that in neo- In one neonate, recovery was not nates. The mean half-life was 1.06 possible because the neonate did not THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 293

TABLE 12 Urinary excretions of Cefazolin in children

TABLE 13 Plasma levels of Cefmetazole in neonates

TABLE 14 Plasma levels of Cefmetazole in children 294 SAKATA

TABLE 15 Urinary excretions of Cefinetazole in neonates

Fig. 18. Plasma levels of Cefmetazole Fig. 19. Urinary excretions of Cef metazole (Intravenously) THE PHARMACOHINETIC STUDIES OF ANTIBIOTICS 295

TABLE 16 Urinary excretions of Cefinetazole in children

void in the 6 hour period. There was required less than one milliliter of no urination during the initial 2 hour specimen for analysis. Many methods period in the fourth neonate, who showed have been employed for the measurement the maximum value of 260 ,ƒÊg/ml in the of antibiotic concentrations in blood, next 2 hour period. In the other three including cylinder method, disc method neonates, the mean maximum value and agar-well method. We made com- was 593±386 ,ƒÊg/ml and the range was parative studies in the rabbits using 268 to 1, 020 ,ƒÊg/ml in the initial 2 hour these three methods with venous and period and the mean recovery rate was capillary blood specimens of adminis- 23.0•}9.5% with the range of 14.0-32.0% tered CET. The blood samples obtained in the 6 hour period, which is less by by microcapillary puncture were exam- 33.0% and 48.6% for CET and CEZ, ined for the concentrations of the drug respectively (Table 15, Fig. 19). In by the disc method and agar-well older children, the mean maximum method. The blood samples obtained by value was 2,143•}512 ƒÊg/ml in the ini- venous puncture were examined by tial 2 hour period and the mean urinary cylinder, disc and agar-well methods. rate was 35.9•}4.5% in the 6 hour The results obtained from each of the period. This is 12.9% higher than in three methods correlated well with one neonates and 40.2% lower than CET another. Although the disc and agar-well and 38.7% lower than CEZ in older method requires small volumes of blood children, respectively (Table 16). for analysis, technical problems limit usefulness of bioassay, for example, long measuring times, generally 18-20 DISCUSSION hours, or the inability to measure concentrations of more than two drugs Pharmacokinetic study of antibiotics simultaneously (Kavanagh, 1960, Simpson, in neonates has benefited greatly from 1963 and Bennett et al., 1966). Many the development of the microassay which rapid bioassays, however, have been 296 SAKATA

reported although the drugs whose mean urinary recovery rate of CET concentrations can be determined are during 6 hour period in neonates and limited (Fame and Knight, 1968, Noone older children were 36.9% and 66.0 56, et al., 1973, Shanson et al., 1976 and respectively. Those of DACET were Jorgensen and Lee, 1977) 49.5% and 25.4%, respectively. Namely, Recently, the HPLC technique has the DACET/CET ratio of urinary re- been successfully implemented for rapid, covery during 6 hour period in neonates accurate, and specific measurements is higher than that in older children. of antibiotics requiring only small This result in older children is similar volumes of sample. In our study, for to data obtained in the adult volunteers example, only 50 al of blood was neces- (Nakagawa et al., 1976). There has been sary to assay for CET in less than one no data in neonates to data. Yamasaku hour. We demonstrated that CET results et al. (1976), however, reported that from HPLC correlated well with the the DACET/CET of urinary recovery results obtained by the standard bio- became higher in renal failure patients assay techniques. at 4 hours after injection of CET than We measured plasma CET levels af- that in healthly adults. The same result ter intravenous administration of a was also reported by Nilsson-Ehle, I. dose of 20 mg/kg by bioassay and HPLC. and Nilsson-Ehle, P. (1979). Therefore, In both neonates and older children, the difference between neonates and blood CET concentrations reached sim- older children may be due to immatu- ilar mean maximum values of 60.7 ƒÊg/ rity of renal function. ml in 15 min. The mean half-life, The mean peak plasma level of CEZ however, were markedly different, 1.47 was 91.8 ƒÊg/ml at 30 min. after injec- hour for neonates, including a 2.06 tion. This result is similar to data hours value for a three day old neonate, reported by Toyonaga (1979). In older as compared to 0.3 hour for older children. children, the mean peak plasma level These data are consistent with the of 122.9 ƒÊg/ml was obtained at 15 min. results reported by Kurosu (1979). The after administration. The mean half- half-lives of CET in older children are lives of CEZ in neonates and older similar to those in adults (Kurosu, children were 4.05 hours and 0.95 hour, 1979). respectively. The mean urinary recovery The same results were obtained in rates of CEZ in neonates and older pharmacokinetic assay by HPLC. We children during 6 hour period were measured plasma DACET/CET ratios in 36.2% and 71.6 %, respectively. This neonates and older children. The ratios difference between neonates and older in neonates and older children were children is also consistent with the 0.21-0.31, 0.12-0.3, respectively, during results reported by Toyonaga (1979). first one hour. The results are consis- The mean maximum plasma level of tent with data obtained by Fujii CMZ in neonates was 34.1 ,ƒÊg/ml at 15 et al. (1977). The following DACET/ min. after injection. In older children, CET ratios became gradually larger; the mean maximum plasma level was these results suggest a longer half-life 194.2 ƒÊg/ml, also obtained at 15 min. of DACET than that of CET in The half-lives of CMZ in neonates and neonates. The maximum urinary excre- older children were 1.75 hour and 1.06 tion of CET was seen 0-2 hours after hour, respectively. The value for neo- injection for older children and 0-2 nates is shorter than that reported by hours or 2-4 hours for neonates. The Fujii et al. (1980). The mean maximum THE PHARMACOKINETIC STUDIES OF ANTIBIOTICS 297

urinary excretion of CMZ was seen in neonates including premature babies. Jpn . during first 2 hour period. The urinary J. Pediat. 30, 49-55. recovery rates of CMZ during 6 hour FUJII, R. (1980). Pharmacokinetics of cefme- period in neonates and older children tazole (CS-1170) in neonates including pre- mature babies. The 28 th congress of Japan were 23.0% and 35.9% . The urinary society of chemotherapy, Tokyo. recovery rate of CMZ was lowest among JORGENSEN, J. H. and LEE, J. C. (1977). Rapid the three antibiotics. bioassay for clindamycin alone and in the presence of aminoglycoside antibiotics. J. Although it is well known that the Infectious Diseases, 136, 422-427. drug of first choice in the initial KAVANAGH, F. (1960). A commentary on mi- treatment of bacterial infections in crobiological assaying. Advan. Appl. Micro- neonates is currently alone biol. 2, 65-93. or in combination with gentamicin, KUROSU, Y. (1979). Study of serum levels of these three antibiotics, which are antibiotics in neonates. Jpn. J. Antibiotics. members of the family, are 32, 1009-1016. LEAST, C. J., WIEGAND, N. J.. JOHNSON, G. F. the drugs of the first choice for in- and SOLOMON, H. M. (1977). Quantitative fections caused by gram negative rods. gas-chromatographic flame-ionization method Therefore, it is important to under- for chloramphenicol in human serum. Clin. stand the pharmacokinetics of these Chem. 23, 220-222. three antibiotics. MINSHEW, B. H., HOLMES, R. K. and BAXTER, C. R. (1975). Comparison of radioimmunoas- say with an enzymatic assay for gentamicin. Antimicrob. Agents Chemother. 7, 107-109. ACKNOWLEDGEMENTS NILSSON-EHLE, I. (1977). High-pressure liquid chromatography as a tool for determination I would like to acknowledge the continu- of antibiotics in biological fluids. Acta. Path. ing guidance and encouragement of Professor Microbiol. Scand. Sect. B, Suppl. 259, 61-66. Fumio Yamashita, and I wish to thank As- NILSSON-EHLE, I. and NILSSON-EHLE, P. (1979). sociate Professor Takashi Motohiro for his Pharmacokinetics of cephalothin. Accumula- kindness and helpful advice. I would also like tion of its deacetylated metabolite in uremic to express my appreciation to Dr. Takeo patients. J. Infectious Diseases. 139, 713-716. Hashimoto and Dr. Hirohumi Nakashima. NAKAGAWA, K., SUZUKI, T. and KOYAMA, M. (1976). Absorption, excretion and metabolism of cephacetrile as compared with cephalothin and cef azolin. Chemotherapy, 24, 118-128. REFERENCES NOONE, P., PATTISON, J. R. and SLACK, R. C. B. (1973). Rapid antibiotic assay. Lancet, 10, BENNETT, J. V., BRODIE, J. L., BENNER, E. J. 315-316. and KIRBY, W. M. M. (1960). Simplified, SHANSON, D. C., HINCE, C. J. and DANIELS, J. accurate method for antibiotic assay of V. (1976). Rapid microbiologic assay of to- clinical specimens. Appl. Microbiol. 14, bramycin. J. Infectious Diseases, 134, 104- 170-177. 109. FAINE, S. and KNIGHT, D. C. (1968). Rapid SHIRKEY, H. C. (1980). General principles of microbiological assay of antibiotics in blood treatment. In "Pediatric therapy, 6th edn"., and other body fluids. Lancet, 17, 375-378. pp. 1-13, Ed. Shirkey, H. C. The C. V. FUJII, R., CHO, N., HORI, M., ICHIHASHI, Y., Mosby Co., St. Louis. IWAI, N., KOBAYASHI, Y., MATSUDA, S., SIMPSON, J. S. (1963). Microbiological assay MATSUDA, S., NAKAZAWA, S., NISHIMURA, T., using large plate methods. In "Analytical SHIBATA, K., TAKASE, Z., YAGISAWA, Y., Microbiology". pp. 87-127 Ed. Frederik YAMADA, F., YAMASHITA, F. and YOSHIOKA, Kavanagh, Academic Press, Inc., New York. H. (1977). Pharmacokinetics of cepholothin STEVENS, P., YOUNG, L. S. and HEW ITT, W. L. 298 SAKATA

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