Advancing Novel Anesthetics Pharmacodynamic and Pharmacokinetic Studies of Cyclopropyl-Methoxycarbonyl Metomidate in Dogs

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Advancing Novel Anesthetics Pharmacodynamic and Pharmacokinetic Studies of Cyclopropyl-methoxycarbonyl Metomidate in Dogs

Jason A. Campagna, M.D., Ph.D., Kevin Pojasek, Ph.D., David Grayzel, M.D., John Randle, Ph.D., Douglas E. Raines, M.D.

ABSTRACT

Background: Cyclopropyl-methoxycarbonyl metomidate (CPMM, also known as ABP-700) is a second-generation “soft” (i.e., metabolically labile) etomidate analogue. The purpose of this study was to characterize CPMM’s pharmacology in beagle Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 dogs in preparation for potential first in human phase 1 clinical trials. Methods: CPMM’s and etomidate’s hypnotic activity and duration of action were assessed using loss of righting reflex and anesthesia score assays in three or four dogs. Their pharmacokinetics were defined after single bolus administration and single bolus followed by 2-h infusion. Adrenocortical recovery times after single bolus followed by 2-h infusion of CPMM, propofol, etomidate, and vehicle were measured using an adrenocorticotropic hormone stimulation test.

Results: Compared with etomidate, CPMM was half as potent as a hypnotic (ED50 approximately 0.8 mg/kg), was more rapidly metabolized, and had a shorter duration of sedative–hypnotic action. Recovery times after CPMM administration were also independent of infusion duration. After hypnotic infusion, adrenocorticotropic hormone–stimulated plasma cortisol concentrations were 4- to 27-fold higher in dogs that received CPMM versus etomidate. Adrenocortical recovery was faster in dogs after CPMM infusion versus etomidate infusion (half-time: 215 vs. 1,623 min, respectively). Adrenocortical responsiveness assessed 90 min after CPMM infusion was not significantly different from that after propofol infusion. Conclusion: The studies in dogs confirm that CPMM has hypnotic and adrenocortical recovery profiles that are superior than those of etomidate, supporting the continued development of CPMM as a clinical sedative–hypnotic to be used as a single bolus and by continuous infusion to induce and maintain general anesthesia or procedural sedation. (Anesthesiology 2014; 121:1203-16)

TOMIDATE entered into clinical practice in 1972 What We Already Know about This Topic E and because of its many favorable properties, it gained popularity as a single bolus agent to induce anesthesia and • Cyclopropyl-methoxycarbonyl metomidate is a metabolically labile etomidate analogue that has many of the desirable prop- as a continuous infusion drug to maintain anesthesia or pro- erties of etomidate, with faster hypnotic recovery and less ad- 1 vide sedation. Unfortunately, recovery times from etomidate renocortical suppression in rats infusions are highly variable, and at hypnotic doses, etomidate • Studies in larger, nonrodent species are needed to better un- also inhibits the cytochrome P450 enzyme 11β-hydroxylase, derstand the pharmacology of cyclopropyl-methoxycarbonyl metomidate producing suppression of adrenocortical steroid synthesis that persists long after the hypnotic effects dissipate.2–10 The What This Article Tells Us That Is New potential serious consequences of such potent and persistent • Recovery of dogs from the hypnotic effect of cyclopropyl-me- adrenocortical suppression led clinicians to abandon the use thoxycarbonyl metomidate was rapid, with recovery times that of etomidate infusions and, while still controversial, have also were independent of infusion duration raised concerns about the administration of a single etomi- • Adrenocortical recovery was faster after cyclopropyl-methoxy- 11–18 carbonyl metomidate infusion than after etomidate infusion date bolus for anesthetic induction. • Adrenocortical responsiveness 90 min after cyclopropyl-me- Several years ago, we developed the hypothesis that ultra– thoxycarbonyl metomidate infusion did not differ from that short-acting analogues of etomidate could be designed that after propofol infusion would retain many desirable properties of etomidate, but afford faster hypnotic recovery and remove any clinically significant adrenocortical suppression.19 We established proof- etomidate but found that its pharmacological proper- of-principle by synthesizing the prototypical “soft” (i.e., ties were not suitable for clinical development.19–22 Subse- metabolically labile) etomidate analogue methoxycarbonyl quent efforts at rational optimization of methoxycarbonyl

Submitted for publication February 27, 2014. Accepted for publication July 28, 2014. From the Medicines Company, Inc., Parsippany, New Jersey (J.A.C.); Annovation BioPharma, Inc., Cambridge, Massachusetts (K.P., D.G., J.R.); and Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (D.E.R.). Copyright © 2014, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins. Anesthesiology 2014; 121:1203-16

Anesthesiology, V 121 • No 6 1203 December 2014 The Pharmacology of CPMM in Dogs

etomidate’s pharmacology led to the synthesis and study of performed at VivoPath, Inc. (Worcester, MA) and their Ani- more than a dozen new analogues, of which cyclopropyl- mal Care and Use Committee approved all protocols before methoxycarbonyl metomidate (CPMM, also known as initiation of any study. Young male beagle dog littermates ABP-700) exhibited the most promising pharmacology in weighing between 5.2 and 9.2 kg at the time of study were rats (fig. 1) and became the lead candidate for advancement used. All four animals participated, on different occasions, in to human trials.23–25 all studies except the single bolus pharmacokinetic studies in Although rats are commonly used as the initial animal which only three dogs were used. For single-bolus hypnotic model to assess the pharmacology of new therapeutic agents, potency and duration studies, animals were dosed up to studies in larger nonrodent species provide additional twice each day. For all other studies (i.e., behavioral recovery, insights into the pharmacology, safety, and efficacy of novel pharmacokinetic, and adrenocortical suppression studies), drug candidates.26,27 Therefore, global regulatory authorities animals were given at least 6 days to recover between dosing. Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 require studies in a nonrodent species as part of any inves- Animals were housed with 12-h light–dark cycles (lights on tigational new drug application intended to advance a new at 7:00 am and off at 7:00 pm). Test drug and vehicle were chemical entity into human clinical testing.28,29 In this arti- administered through a 22-gauge IV catheter located in a cle, we report the results of studies conducted to define the saphenous vein. pharmacology of CPMM in dogs. Our goal in this work was to characterize the pharmacodynamic and pharmacokinetic Sources and Formulation of Hypnotic Drugs properties of CPMM with the purpose of advancing knowl- Cyclopropyl-methoxycarbonyl metomidate was synthesized edge about this potential new anesthetic agent. by Aberjona Laboratories (Beverly, MA) using the approach described previously and formulated (8 mg/ml) as an aque- Materials and Methods ous solution with 20% sulfobutylether-β-cyclodextrin 23 The methodology of the in vivo laboratory studies was dic- (adjusted to pH 7.4). The formulated drug was stored fro- tated in part by international guidelines established by the zen at −20°C with ongoing stability testing of representative International Conference on Harmonisation of Techni- batches demonstrating no significant degradation over time. cal Requirements for Registration of Pharmaceuticals for Etomidate was purchased from BaChem (Torrance, CA) and Human Use and, as a result, may differ from those routinely formulated (2 mg/ml) as an aqueous solution in 35% pro- encountered for research studies of this type. pylene glycol. CPMM and etomidate solutions were sterile filtered through a 0.2-µm polysulfone filter before dosing. Animals Propofol (10 mg/ml) was purchased from Abbott Laborato- All animal studies were conducted in accordance with the ries (Abbott Park, IL) formulated in the standard emulsion. Final Rules of the Animal Welfare Act regulations, the Public Health Service Policy on Humane Care and Use of Labora- Hypnotic Potency and Duration of Hypnotic Action tory Animals from the Office of Laboratory Animal Wel- By using a loss of righting reflexes (LoRR) assay, hypnotic fare of the National Institutes of Health, and the Guide for potencies and durations of hypnotic action were assessed the Care and Use of Laboratory Animals from the National in dogs. The desired dose of hypnotic (CPMM or etomi- Research Council. Animals (n = 4 dogs) were purchased date) was rapidly (<5 s) injected intravenously followed by a from Marshall BioResources (North Rose, NY). Studies were normal saline flush. Immediately after injection, dogs were turned onto their sides. A dog was judged to have LoRR if it failed to immediately right itself (onto all four paws) after drug administration. A stopwatch was used to measure the duration of LoRR, which was defined as the time from drug injection until spontaneous righting.

Dosing of Hypnotic Drugs for Behavioral, Pharmacokinetic, and Adrenocortical Recovery Studies In all studies, the goal was to attain an intermediate depth of hypnosis/anesthesia, which we defined as an anesthesia score of 3 (table 1). For all studies, this was achieved with a rapid (<5 s) bolus dose of 3 to 4 mg/kg for CPMM, 2 mg/ kg for etomidate, or 5 to 6 mg/kg for propofol. Because of its low therapeutic index,30 propofol boluses were given at 1 mg/kg increments every 20 s until an anesthesia score of Fig. 1. Chemical structures of etomidate and cyclopropyl- 3 was reached. For 2-h maintenance studies, this bolus was methoxycarbonyl metomidate (CPMM) and their respective followed by a 2-h continuous infusion. During these 2-h primary metabolites. infusions, the infusion rates were adjusted between 0.5 to

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1.0 mg kg−1 min−1 for CPMM, 0.1 to 0.15 mg kg−1 min−1 into prechilled collection tubes containing EDTA. Esterase for etomidate, and 0.4 to 0.5 mg kg−1 min−1 for propofol to activity in the collected blood was immediately inactivated maintain an anesthesia score of 3. For 2-h infusion studies by the addition of acetonitrile. Blood samples were main- comparing recovery after CPMM versus etomidate, behav- tained chilled (0° to 4°C), centrifuged within 30 min, and ioral, pharmacokinetic, and adrenocortical studies were done the plasma stored at −80°C until analyzed. Plasma concen- simultaneously in each individual dog. During 2-h infusion trations of CPMM, etomidate, and their respective primary studies, dogs could receive midazolam (0.1 to 0.2 mg/kg IV metabolite were quantified by Nextcea, Inc. (Woburn, MA) bolus per dose) as required to suppress involuntary move- using a high-performance liquid chromatography mass ments (i.e., myoclonus). In pilot experiments, such dosing spectrometry assay coupled with tandem mass spectrom- had no discernable sedative effect but in our studies effec- etry. Samples (20 µl) were injected onto a Luna C8 RP (5 tively reduced the myoclonus. During hypnotic infusions µm, 2.0 × 50 mm) column using a CTC Analytics HTS Pal Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 and until anesthetic emergence, supplemental oxygen was Autosampler (Zwingen, Switzerland) and an Agilent binary supplied to dogs by facemask. 1100 LC pump (Santa Clara, CA). The high-performance liquid chromatography mobile phases were (phase A) 0.1% Behavioral Recovery after Hypnotic Bolus or Hypnotic formic acid in water (v/v) and (phase B) 0.1% formic acid in Bolus Followed by Continuous Infusion: Assessment 90/10 acetonitrile/water (v/v). The gradient ran from 25 to Using an Anesthesia Scale 90% phase B in 2.6 min and the flow rate was 0.3 ml/min. Anesthetic depth was quantified using a subjective numeri- The total running time per sample was 4 min. The analytes cal anesthesia scale similar to that used in the study reported were detected with an API 5000 triple quadrupole mass spec- by Silva et al. (table 1).31 This scale ranged from a score of trometer (AB SCIEX, Framingham, MA). The intensities of 0 (fully awake and alert) to a score of 4 (deep anesthesia). CPMM, etomidate, acid metabolites, and internal standard In some experiments, scores were judged to fall between were determined by integration of extracted ion-peak areas scores of 0 and 1, 1 and 2, or 2 and 3 during recovery. These using Analyst 1.5.1 software (AB SCIEX). Calibration curves were recorded as scores of 0.5, 1.5, or 2.5, respectively, but were prepared by plotting the analyte to internal standard were not included in our analyses because not all dogs were peak area ratio versus concentration. The model for the cali- judged to have attained these intermediate anesthetic depths bration curves was linear with (1/x2) weighting. The CPMM and these scores were not associated with specific behavioral and etomidate calibration curves were linear between 0.1 to endpoints. For single-bolus-only studies, anesthetic depth 250 ng/ml with 75% or more of the standards (two repli- was assessed and the anesthetic score recorded at times 0 cates of eight concentrations) and 67% or more of the QCs (i.e., immediately before drug administration), 9, 15, and (three replicates of three concentrations) within ±15% of the 30 s after hypnotic administration, and every 30 s thereafter spiked concentration. The CPMM metabolite and etomi- until dogs fully recovered. For studies using a single bolus date metabolite calibration curves were linear between 5 to followed by 2-h hypnotic maintenance infusion, anesthetic 1,000 ng/ml with 75% or more of the standards (two repli- depth was intermittently assessed and the anesthetic score cates of seven concentrations) and 67% or more of the QCs recorded until dogs fully recovered. (three replicates of three concentrations) within ±15% of the spiked concentration. Handling of Blood Samples for Pharmacokinetic Studies At the desired time points after hypnotic administration Pharmacokinetic Modeling (either single bolus alone or single bolus followed by 2-h infu- Pharmacokinetic parameters were derived by noncompart- sion), blood samples (approximately 1 ml) were drawn from mental methods using Phoenix WinNonlin Version 6.3 an IV catheter placed in the cephalic vein and transferred (Pharsight Corp., Cary, NC).32 The following parameters for

Table 1. Behavioral Assessment and Associated Anesthesia Scale

Anesthesia Depth Behavioral Signs Anesthesia Scores*

Awake Fully awake and alert 0 Sedated Mildly impaired but responsive to stimulation and with righting 1 reflexes present Shallow anesthesia Righting reflexes lost but responds to stimulation (e.g., presence of 2 oximeter probe on the tongue) Medium anesthesia Responds only to painful stimulation (e.g., paw pinch). No response 3 to oximeter probe on the tongue Deep anesthesia Unresponsive to painful stimuli, reduced respirations, oxygen desaturation 4

* Scores of 0.5, 1.5, or 2.5 were sometimes recorded during recovery when behavior was judged to fall between scores 0 and 1, 1 and 2, or 2 and 3, respectively.

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each analyte were derived, where appropriate, from individ- Adrenocortical Recovery after Hypnotic Infusion ual plasma concentration–time profiles in individual dogs: Anesthesia was induced and maintained for 2 h at an anesthesia score of 3 with the desired hypnotic agent (CPMM, C the plasma concentration after IV bolus adminis- 0 propofol, or etomidate) as described above under Dosing of tration at t = 0 min determined by WinNonlin by Hypnotic Drugs for Behavioral, Pharmacokinetic, and Adre- back-extrapolation from the initial concentration– nocortical Recovery Studies. To minimize baseline cortisol time points. concentrations and increase the sensitivity of the assay, C the maximum observed plasma concentration. max endogenous adrenocorticotropic hormone (ACTH) produc- t the time of occurrence of C . max max tion was suppressed by intravenously administering dexa- λ the apparent terminal elimination rate constant, cal- z methasone (0.10 mg/kg) at the start of hypnotic infusions

culated as the absolute value of the slope of the ter- Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 (t = 0 min) and then every 2 h during the study (t = 120 minal phase of the natural log-transformed plasma and 240 min). For studies comparing adrenocortical respon- concentration-versus-time curve. siveness after infusion of CPMM and etomidate, a control t the apparent terminal half-life, calculated as ln 2/λ . 1/2 z group that received a bolus followed by infusion of CPMM’s AUC the area under the plasma concentration-versus- vehicle was also studied. At the desired times after the 2-h time curve from time zero to infinity, calculated hypnotic or vehicle infusion ended, ACTH (250 µg) was from AUC + C /λ , where C is the concentration 1–24 last t z t administered intravenously at 90-min intervals and blood at the last measurable time point. samples were drawn every 30 min. Plasma cortisol concen- Vz the apparent volume of distribution in the terminal trations in sampled blood were quantified using an enzyme- phase, calculated as dose/(λ × AUC) for the dosed z linked immunosorbent assay (Nextcea, Inc.). drug Vss the apparent volume of distribution at steady state, Statistical Analysis calculated as dose × area under the first moment Unless indicated otherwise, data points are reported as curve/(AUC )2 for the dosed drug. inf mean ± SD and fitted parameters are reported as mean with CL systemic clearance, calculated as dose/AUC for the inf 95% CIs. For values defined by the ratio of two experi- dosed drug mental values (i.e., the normalized cortisol concentration), Nominal sampling times were used for all calculations of the reported SD was determined by error propagation. pharmacokinetic parameters. Plasma concentrations below Anesthetic recovery times from an anesthesia score of 3 (to the limit of quantitation of the assay were taken as zero if lower scores) after hypnotic administration were compared they occurred before the first measurable time point and as between the two hypnotic groups using a two-way ANOVA missing if they occurred after the last measurable time point with a Bonferroni posttest to correct for multiple compari- or in between two measurable time points. For the estima- sons. The factors were anesthesia score and hypnotic group. tion of λz (the apparent terminal elimination rate constant) Plasma cortisol concentrations after hypnotic or vehicle and corresponding t1/2 (the apparent terminal half-life, cal- administration were compared using a two-way ANOVA culated as ln 2/λz) values, three or more points were required with a Tukey multiple comparisons test. Comparisons of in within the terminal phase (Cmax could not be included). In vivo adrenocortical inhibitory potencies were made using an 2 addition, adjusted R for λz (goodness-of-fit statistic for the extra-sum-of-squares F test. Statistical analyses and curve fits terminal elimination phase adjusted for number of points were done using Prism v5.0 for the Macintosh (GraphPad used) was required to be greater than 0.85. Software, Inc., La Jolla, CA) or Igor Pro 6.1 (Wavemetrics, Lake Oswego, OR). Pharmacodynamic Modeling For CPMM and etomidate, the relation between plasma Results hypnotic concentrations and anesthesia scores upon bolus Hypnotic Activity of CPMM and Etomidate 33 injection were fit to a sigmoid Emax model (equation 1) : Our first studies in dogs were designed to confirm CPMM’s γ hypnotic activity in a large nonrodent species using an LoRR CtE () Et()= EXmax γ where: E(t) is the anesthesia assay and to establish potency for subsequent behavioral Ct+ ECγ E () AS recovery experiments. CPMM was administered as an IV score at time t; Emax is the maximum anesthesia score, which bolus and rapidly (<15 s) induced LoRR in all dogs at doses is a fixed value of 4 on our scale; Ce(t) is the plasma hypnotic 1 mg/kg or greater, whereas lower doses (i.e., 0.25 or 0.5 mg/ concentration at time t; ECAS is the plasma concentration kg) failed to induce LoRR in any dog (fig. 2A). For dogs that when anesthesia scores are 25, 50, and 75% of the maximal had LoRR, the duration of LoRR increased approximately anesthesia score and correspond to anesthesia scores of 1, linearly with the logarithm of the dose from an average value 2, and 3, respectively; and γ is the slope parameter which of 1.8 ± 0.6 min (at 1 mg/kg, n = 3 dogs) to 10.9 ± 0.7 min (at reflects the steepness of the concentration–response relation. 12 mg/kg, n = 4 dogs; fig. 2B). The X-intercept and slope of

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this relation were 0.88 mg/kg (95% CI, 0.50 to 1.27 mg/kg) (±SD) required for dogs to recover (from an anesthesia score and 9.9 (95% CI, 9.4 to 12.5), respectively.34,35 For compar- of 3) to the indicated anesthesia score after the 2-h infusion ison, we also assessed etomidate’s hypnotic activity in dogs was completed. It shows that the times required for dogs to with bolus doses ranging from 0.5 to 1.9 mg/kg. Over this recover from an anesthesia score of 3 to all lower scores was dose range, etomidate rapidly produced LoRR in all dogs shorter after administration of CPMM versus etomidate, (fig. 2A). The duration of LoRR produced by etomidate with statistical significance achieved at scores of 1 and 0. Our also increased approximately linearly with the logarithm of analysis also showed that there was no difference in the time the dose from 2.7 ± 0.8 min (at 0.5 mg/kg, n = 3 dogs) to required to recover to anesthesia scores of 2, 1, or 0 after 17 ± 5 min (at 1.9 mg/kg, n = 3 dogs; fig. 2B). For etomidate, administering a single bolus of CPMM as compared with the X-intercept and slope of this relation were 0.37 mg/kg that after administering a single bolus followed by a 2-h infu- (95% CI, 0.18 to 0.52 mg/kg) and 24 (95% CI, 15 to 34), sion of CPMM (4.4 ± 1.3 min, 6.0 ± 1.1 min, or 8 ± 3 min Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 respectively, indicating that etomidate was approximately for bolus only vs. 4.3 ± 1.2 min, 5.5 ± 0.7 min, or 11 ± 3 min twice as potent as CPMM in dogs and cleared from the brain for bolus followed by a 2-h infusion). Thus, hypnotic recov- significantly more slowly. ery times after CPMM administration were independent of infusion duration. Behavioral Recovery after Administration of CPMM and During administration of CPMM and etomidate, myoc- Etomidate lonus was observed in some dogs. The myoclonic movements We then quantified the rate at which dogs transitioned from were modest in intensity and consisted primarily of trem- a medium depth of anesthesia to full hypnotic recovery after ors or twitching in the torso and neck. After 2-h infusions, CPMM administration (table 1). As with the LoRR studies, myoclonus persisted long (up to approximately an hour) into we used etomidate (at an approximately equihypnotic dose) the postinfusion period after etomidate infusions but ceased as a comparator. For individual dogs, figure 3A plots the anes- within several minutes after terminating CPMM infusions. thesia score as a function of time after single bolus admin- During CPMM infusion, all the four dogs had myoclonus istration of either CPMM or etomidate. Figure 3B graphs and were given midazolam (a single dose of 0.2 mg/kg to the mean times (±SD) required for dogs to recover (from an two dogs and 0.4 mg/kg in divided doses to two dogs) to anesthesia score of 3) to the indicated anesthesia scores after attenuate the myoclonus. Similarly, during etomidate infu- receiving the hypnotic bolus. The data show that the times sion, two dogs had myoclonus and were given midazolam required for dogs to recover from an anesthesia score of 3 to (a single dose of 0.2 mg/kg to one dog and 0.3 mg/kg in all lower scores were significantly shorter after bolus admin- divided doses to another dog). istration of CPMM as compared with etomidate. For individual dogs, figure 4A plots the anesthesia score In Vivo Pharmacokinetics of CPMM and Etomidate: Single as a function of time as dogs recovered after receiving a Bolus and Infusion Studies single bolus dose of either CPMM or etomidate followed We also measured the time-dependent change in the plasma by a 2-h infusion (using the same hypnotic) that maintains concentration of parent hypnotic and metabolite after an anesthesia score of 3. Figure 4B graphs the mean time administering CPMM or etomidate to dogs as either a single

Fig. 2. Hypnotic activities of cyclopropyl-methoxycarbonyl metomidate (CPMM) and etomidate. (A) CPMM and etomidate dose– response relations for loss of righting reflexes (LoRRs) after bolus administration. The curve is a fit of the CPMM data to a Hill equation with the maximum and minimum constrained to 0 (no LoRR) and 1 (LoRR), respectively, and provides an approximate

ED50 value of 0.8 mg/kg. (B) Duration of LoRRs after bolus administration of either CPMM or etomidate. For both drugs, the duration of LoRR increased linearly with the logarithm of the dose. The respective X-intercept and slope of this relation was 0.88 mg/ kg (95% CI, 0.50 to 1.27 mg/kg) and 9.9 (95% CI, 9.4 to 12.5) for CPMM and 0.37 mg/kg (95% CI, 0.18 to 0.52 mg/kg) and 24 (95% CI, 15 to 34) for etomidate. Each symbol represents data obtained from a single dog experiment.

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Fig. 3. Anesthetic recovery after single bolus administration of cyclopropyl-methoxycarbonyl metomidate (CPMM; n = 4 dogs) or etomidate (n = 3 dogs). (A) Anesthesia score for individual dogs as a function of time upon bolus administration of either CPMM (4 mg/kg) or etomidate (2 mg/kg). CPMM and etomidate group dogs are shown as red and black symbols, respectively. (B) Mean times (±SD) required for dogs to recover to the indicated anesthesia scores (from an anesthesia score of 3) after receiving either CPMM (4 mg/kg) or etomidate (2 mg/kg). **P < 0.01 and *** P < 0.001.

Fig. 4. Anesthetic recovery after a single bolus followed by 2-h infusion of cyclopropyl-methoxycarbonyl metomidate (CPMM; n = 4 dogs) or etomidate (n = 4 dogs). (A) Anesthesia scores for individual dogs as a function of time after receiving a single bolus followed by a 2-h infusion of CPMM or etomidate. CPMM and etomidate group dogs are shown as red and black symbols, respectively. (B) Mean times (± SD) required for dogs to recover to the indicated anesthesia scores (from an anesthesia score of 3) after bolus administration followed by a 2-h infusion of CPMM or etomidate. * P < 0.05 and **** P < 0.0001.

IV bolus or a single bolus followed by a 2-h infusion (fig. 5). CPMM metabolite concentrations. The peak metabolite Figure 5A plots the plasma CPMM and CPMM metabolite concentration (13,750 ± 2,570 ng/ml) was measured in sam- concentrations as a function of time after bolus administra- ples drawn 5 min after bolus CPMM administration. This tion of CPMM (4 mg/kg, n = 3 dogs). The plasma CPMM concentration decreased by one order of magnitude during concentration in the initial blood sample, obtained 30 s the subsequent 115 min of the study. after CPMM administration, was 4,130 ± 640 ng/ml. Plasma Figure 5B plots the plasma etomidate and etomidate CPMM concentrations in blood samples drawn 10 min after metabolite concentrations as a function of time after bolus CPMM administration (i.e., after full hypnotic recovery) administration of etomidate (2 mg/kg, n = 3 dogs) to dogs. were 330 ± 41 ng/ml (i.e., 8% of that measured in the initial The plasma etomidate concentration in the initial blood blood sample). In the final blood samples drawn 2 h after sample, which was obtained 30 s after etomidate administra- CPMM administration, plasma CPMM concentrations had tion, was 9,080 ± 1,390 ng/ml. The plasma etomidate con- decreased by four orders of magnitude from those measured centrations in blood samples drawn 10 min after etomidate in the initial blood sample. The plasma CPMM concentra- administration was 2,230 ± 448 ng/ml (i.e., 25% of that pres- tion range during anesthetic recovery (i.e., the CPMM con- ent in the initial blood sample). In the final blood samples centration present 4.4 to 8 min after bolus administration, drawn 120 min after etomidate administration, the plasma see fig. 3B) was approximately 500 ng/ml. Coincident with etomidate concentration was 1.5 orders of magnitude lower the time-dependent reduction in plasma CPMM concen- than that measured in the initial samples. The plasma etomi- trations, we measured a time-dependent change in plasma date concentration range associated with anesthetic recovery

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Fig. 5. Pharmacokinetics of cyclopropyl-methoxycarbonyl metomidate (CPMM), etomidate and their respective primary metabolites. T = 0 is the time of hypnotic bolus administration (for single-bolus-only studies) or the end of the 2-h hypnotic infusion (for bolus followed by 2-h infusion studies). (A) Time-dependent change in plasma CPMM and metabolite concentrations after administering a single CPMM bolus (4 mg/kg). (B) Time-dependent change in plasma etomidate and metabolite concentrations after administering a single etomidate bolus (2 mg/kg). (C) Time-dependent change in plasma CPMM and metabolite concentrations after administering a single bolus followed by a 2-h continuous infusion of CPMM. (D) Time-dependent change in plasma etomidate and metabolite concentrations after administering a single bolus followed by a 2-h continuous infusion of etomidate. Each data point is the mean ± SD (n = 3 or 4 dogs for each data point).

(i.e., the etomidate concentration present 9.0 to 13.8 min drawn 300 min after the infusion ended. The plasma con- after bolus administration, see fig. 3B) was approximately centration of CPMM metabolite in blood drawn immedi- 1,000 ng/ml. We also measured a time-dependent change in ately before the infusion ended was 36,240 ± 6,970 ng/ml. plasma etomidate metabolite concentrations. This concen- This concentration decreased by two orders of magnitude to tration reached a peak value of 2,330 ± 587 ng/ml in blood 340 ± 200 ng/ml in our final blood samples drawn 300 min samples drawn 10 min after etomidate administration before later. steadily decreasing to 708 ± 75 ng/ml in our final blood sam- Figure 5D shows the plasma etomidate and etomi- ples drawn 120 min after etomidate administration. date metabolite concentrations as a function of time after Figure 5C shows the plasma CPMM and CPMM administering etomidate as a single bolus followed by a 2-h metabolite concentrations in dogs as a function of time after infusion (n = 4 dogs). The plasma etomidate concentra- administering CPMM as a single bolus followed by a 2-h tion in blood drawn immediately before the infusion ended infusion (n = 4 dogs). The plasma CPMM concentration was 2,050 ± 1,090 ng/ml. In the next blood sample drawn in blood drawn immediately before the infusion ended was 30 min later, the plasma etomidate concentration decreased 3,310 ± 740 ng/ml. In the next blood sample (which was to 480 ± 340 ng/ml which is 23% of that measured imme- drawn 30 min after the infusion ended), the plasma CPMM diately before the infusion ended and within the hypnotic concentration was 103 ± 56 ng/ml. This concentration is just range. Plasma etomidate concentrations in subsequent blood 3% of that measured immediately before the infusion ended samples progressively decreased reaching 37 ± 24 ng/ml in and well below that which we associate with full hypnotic blood samples drawn 300 min after the infusion ended. The recovery. After this rapid initial decrease, plasma CPMM plasma concentration of etomidate metabolite was high- concentrations in subsequent blood samples decreased more est in blood drawn immediately before the infusion ended slowly (e.g., by only 22% to 81 ± 27 ng/ml during the next (1,680 ± 250 ng/ml) and decreased by more than an order of 30 min) before reaching 15 ± 12 ng/ml in blood samples magnitude in blood samples drawn 300 min later.

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Table 2. Pharmacokinetic Parameters upon Bolus Administration (n = 3 Dogs)

−1 −1 −1 C0 (ng/ml) t½ (min) AUC (min∙ng ml ) CL (ml∙kg min ) Vss (ml/kg) CPMM 5,180 ± 1,120 16.1 ± 2.99* 19,200 ± 2,590* 211 ± 26** 1,880 ± 569 Etomidate 10,700 ± 1,440 60.1 ± 10.4 139,000 ± 26,300 14.7 ± 2.78 874 ± 172

C (ng/ml) t (min) −1 max max t½ (min) AUC (min∙ng ml ) CPMM metabolite 1,530 ± 1,060 11.7 ± 7.64 30.3 ± 2.09* 858,000 ± 168,000* Etomidate metabolite 2,370 ± 347 18.3 ± 18.9 61.4 ± 9.13 236,000 ± 18,400

CPMM vs. etomidate or CPMM metabolite vs. etomidate metabolite: * P < 0.05; ** P < 0.01.

AUC = the area under the plasma concentration vs. time curve from time zero to infinity; C0 = the plasma concentration after bolus administration at Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 t = 0 min; CL = systemic clearance; Cmax = the maximum observed plasma concentration; CPMM = cyclopropyl-methoxycarbonyl metomidate; t1/2= the apparent terminal half-life; tmax = the time of occurrence of Cmax; Vss = the apparent volume of distribution at steady state.

We modeled the time-dependent change in the venous elimination half-lives of the two drugs was not significantly concentrations of CPMM and etomidate (and their respec- different with values of 96.8 ± 38.5 min and 88.1 ± 14.1 min tive metabolites) in each dog using noncompartmental for CPMM and etomidate, respectively (P = 0.6788). analysis. The mean ± SD values for the derived parameters For a single representative dog, figure 6, A and B, plots are shown in tables 2 and 3 for single bolus and single the time-dependent change in plasma hypnotic concentra- bolus followed by 2-h infusion studies, respectively. After tions and anesthesia scores upon bolus administration of the single bolus administration, the concentrations of 4 mg/kg of CPMM (fig. 6A) or 2 mg/kg of etomidate (fig. both CPMM and etomidate declined in a biexponential 6B). For both CPMM and etomidate, anesthesia scores and manner. The terminal elimination half-life of CPMM was plasma concentrations decreased over time after bolus admin- 27% that of etomidate with values of 16.1 ± 2.99 min and istration. Figure 6, C and D, plots for all dogs the relation 60.1 ± 10.4 min, respectively (P = 0.0195). Similarly, clear- between the anesthesia score and the plasma hypnotic con- ance of CPMM was 14 times higher than that of etomidate centration after bolus administration of 4 mg/kg of CPMM with values of 211 ± 26 ml kg−1 min−1 and 14.7 ± 2.78 ml (fig. 6C) or 2 mg/kg of etomidate (fig. 6D). Fits of these data kg−1 min−1, respectively (P = 0.0062). In the case of CPMM to equation 1 yielded the venous concentrations of CPMM (but not etomidate), clearance exceeded the total hepatic and etomidate associated with anesthesia scores of 1, 2, or 3 blood flow in dogs (by an order of magnitude), indicating (table 4). that hydrolysis of CPMM to its carboxylic acid metabolite was primarily extrahepatic.36 CPMM’s apparent volume Adrenocortical Recovery after Prolonged Administration of distribution at steady state (1,880 ± 569 ml/kg) was not of CPMM: Comparisons with Propofol and Etomidate only significantly larger than that of etomidate, it was three The adrenocortical recovery profile of CPMM was assessed times greater than the total body water volume in dogs and compared with that of the commonly infused hypnotic 37 (600 ml/kg). This suggests significant CPMM distribution propofol by inducing and maintaining dogs under anesthesia into tissues. The area under the concentration-versus-time for 2 h (at an anesthesia score of 3) with either CPMM or pro- curve also significantly differed between CPMM and etomi- pofol and then measuring ACTH -stimulated plasma corti- −1 1–24 date with respective values of 19,200 ± 2,390 min ng ml sol concentrations in serially drawn blood samples (n = 4 dogs −1 and 139,000 ± 26,300 min ng ml (P = 0.0014). After sin- per group). During these studies, myoclonus was observed gle bolus followed by 2-h infusion, the difference in terminal with both CPMM and propofol. During CPMM infusion, all four dogs had myoclonus and were given midazolam (0.4 mg/ Table 3. Pharmacokinetic Parameters after Bolus Followed by kg in divided doses to two dogs and 0.6 mg/kg in divided 2-h Infusion (n = 4 Dogs) doses to two dogs) to eliminate myoclonus. During propofol infusion, two dogs had myoclonus and were given midazolam C (ng/ml) t (min) max ½ (0.2 mg/kg to each dog). Figure 7 plots the plasma cortisol CPMM 3,310 ± 740* 96.8 ± 38.5 concentrations at the indicated times after hypnotic infusion Etomidate 2,050 ± 1,090 88.1 ± 14.1 termination and upon stimulation with ACTH1–24. In both C (ng/ml) hypnotic groups, plasma cortisol concentrations increased max t½ (min) after ACTH administration, and adrenal responsiveness to CPMM Metabolite 36,200 ± 6,970** 92.6 ± 34.5 1–24 ACTH was virtually identical between dogs that received Etomidate Metabolite 1,680 ± 253 69.3 ± 23.4 1–24 CPMM and those that received propofol. CPMM vs. etomidate or CPMM metabolite vs. etomidate metabolite: We also compared the adrenocortical response recovery * P < 0.05; ** P < 0.01. profile after administration of CPMM to that after admin- Cmax = the maximum observed plasma concentration; CPMM = cyclopropyl-methoxycarbonyl metomidate; t1/2= the apparent terminal half-life. istration of etomidate as the latter is known to produce

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Fig. 6. Relation between venous plasma hypnotic concentrations and anesthesia scores after bolus administration of cyclopropyl-methoxycarbonyl metomidate (CPMM) or etomidate. (A) Time-dependent change in the plasma CPMM concentration and the anesthesia score upon bolus administration of 4 mg/kg of CPMM to a single dog. Open red circles indicate CPMM concentrations. Closed black circles indicate anesthesia scores. (B) Time-dependent change in the plasma etomidate concentration and the anesthesia score upon bolus administration of 2 mg/kg of etomidate to a single dog. Open red circles indicate CPMM concentrations. Closed black circles indicate anesthesia scores. (C) Relation between the anesthesia scores and plasma CPMM concentrations after bolus administration of 4 mg/kg of CPMM (n = 3). (D) Relation between the anesthesia scores and plasma etomidate concentrations after bolus administration of 2 mg/kg of etomidate (n = 3). Data shown in A and B are from the same dog. In C and D, identical symbols represent the data obtained from a single dog experiment. The curves are fits of the data from all dogs to equation 1 with fitted parameters given in table 3. In C and D, the dashed lines indicate the hypnotic concentrations that produce 25, 50, and 75% of the maximum anesthetic depth. These anesthetic depths correspond to anesthesia scores of 1, 2, and 3, respectively.

Table 4. Pharmacodynamic Parameters upon Bolus Administration (n = 3 Dogs)

EC ECanesthesia score 1 ECanesthesia score 2 anesthesia score 3 (95% CI), ng/ml (95% CI), ng/ml (95% CI), ng/ml γ (95% CI)

CPMM 520 (297–911) 1,206 (894–1,627) 2,798 (1,840–4,256) 1.3 (0.7–1.9) Etomidate 1,607 (1,026–2,517) 3,092 (2,425–3,944) 5,952 (4,392–8,066) 1.7 (0.9–2.4)

CPMM = Cyclopropyl-methoxycarbonyl metomidate; ECanesthesia score 1 = venous plasma concentration when the anesthesia score is 1; ECanesthesia score 2 = venous plasma concentration when the anesthesia score is 2; ECanesthesia score 3 = venous plasma concentration when the anesthesia score is 3; γ = slope parameter. adrenocortical suppression in dogs similar to humans.38–40 The CPMM-treated animals exhibited a normal adrenal In these studies, we induced and maintained dogs at an response to the second ACTH challenge (180 min postin- anesthesia score of 3 for 2 h with either CPMM or etomi- fusion) when compared with the vehicle control, whereas date (n = 4 dogs per group). We also included a vehicle the etomidate-treated animals continued to show adrenal group as a control that received CPMM’s vehicle only. hyporesponsiveness. Plasma cortisol concentrations in the Figure 8A plots the plasma cortisol concentration in dogs etomidate-treated group remained significantly lower than at the indicated times after infusion with CPMM, etomi- those in the vehicle group throughout the duration of the date, or vehicle and upon stimulation with ACTH1–24. study (>300 min), whereas plasma cortisol concentrations In both hypnotic groups, plasma cortisol concentra- in the CPMM group were not significantly different from tions were lower than vehicle-treated animals at the first controls for all time points longer than 120 min after infu- postinfusion sample drawn 30 min after infusion termina- sion termination. At equivalent postinfusion time points, tion (and administration of the first dose of ACTH1–24). plasma cortisol concentrations were 4- to 27-fold higher

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in blood drawn from dogs in the CPMM group compared Discussion with those in the etomidate group. For each time point after These are the first studies to define the pharmacology of infusion, the inset in figure 8A plots the plasma cortisol the soft etomidate analogue CPMM in a large nonrodent concentration in each hypnotic group normalized to that species. They show that in beagle dogs, CPMM is a rapidly in the vehicle control group. It shows that after the hyp- metabolized and ultra–short-acting hypnotic agent with a notic infusions ended, plasma cortisol concentrations in potency that is approximately half that of etomidate. Unlike blood drawn from both hypnotic groups recovered steadily etomidate however, CPMM has a hypnotic recovery profile over time toward those of the vehicle control group. The that is independent of infusion duration with full recovery half-time for that recovery was calculated from that data from a medium depth of anesthesia occurring as quickly to be 215 min (95% CI, 152 to 362 min) in the CPMM after single bolus administration as after single bolus fol- Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021 group and 1,623 min (95% CI, 1,041 to 3,673 min) in the lowed by a 2-h infusion. In addition, we found that CPMM etomidate group (P < 0.0001). and propofol have equivalent adrenocortical recovery pro- Together, the pharmacokinetic (fig. 5, C and D) and files and that ACTH1–24-stimulated cortisol concentrations adrenocortical data (fig. 8A and inset) allow us to broadly increase much more rapidly after CPMM infusion than after assess the relation between the plasma hypnotic concen- etomidate infusion. tration (determined in the former) and adrenocortical The current studies also indicate that CPMM’s hypnotic responsiveness to ACTH1–24 stimulation (determined in the actions in dogs are similar to that previously observed in latter). Figure 8B plots that relation and shows that when rats. In both species, anesthetic induction is fast and hyp- plasma concentrations of CPMM or etomidate were high notic potency is high (hypnotic ED50 approximately 0.8 and soon after infusions ended, adrenocortical responsiveness 0.69 mg/kg in dogs and rats, respectively).23 The duration of (as reflected by normalized plasma cortisol concentrations) hypnosis increases approximately linearly with the logarithm was low. From these data, we estimated in vivo half-inhibi- of the dose in both species with slopes for this relation that tory concentrations of 27 ng/ml (95% CI, 22 to 32 ng/ml) are similar (9.9 and 6.9 in dogs and rats, respectively).23 In for CPMM and 16 ng/ml (95% CI, 8.5 to 30 ng/ml) for dogs and rats, hypnotic recovery times are independent of etomidate (P = 0.0234). In the case of etomidate, the esti- infusion duration and occur on similar time scales after 2-h mated half-inhibitory concentration for adrenal steroido- continuous CPMM infusions (5.5 and 4.2 min in dogs and 24 genesis correlates well with the IC50 of this drug defined in rats, respectively). 41,42 previous reports. Cyclopropyl-methoxycarbonyl metomidate’s actions on the adrenocortical system are also similar in rats and dogs.25

As in rats, adrenocortical responsiveness to ACTH1–24 stimulation in dogs is suppressed during CPMM infusion.

However after infusion, ACTH1–24-stimulated plasma cortisol concentrations recover much more quickly after CPMM than after etomidate. The current studies in dogs further show that within 90 min after ending a 2-h infusion, adrenocortical responsiveness after CPMM is equivalent to that observed after propofol. These results suggest that with CPMM, any impact on adrenocortical steroid synthesis after single bolus administration or short-term continuous infusion is likely to be brief, clinically unim- portant, and equivalent to the current clinical standard of care, propofol. These findings in dogs strongly support the further advancing CPMM to potential first in human phase 1 clinical trials. The pharmacokinetic data presented in these studies are helpful for understanding the unique pharmacology of Fig. 7. Adrenocortical response to adrenocorticotropic CPMM when compared with etomidate. To provide a visual hormone (ACTH) stimulation after administration of cyclo- comparison of the two drugs, figure 9 superimposes their propyl-methoxycarbonyl metomidate (CPMM) or propofol. normalized plasma concentrations as a function of time after ACTH -stimulated cortisol concentrations after administer- 1–24 either single bolus administration (fig. 9A) or single bolus ing a single bolus followed by 2-h infusion of CPMM or propo- followed by 2-h infusion (fig. 9B) and indicates the approxi- fol. Infusions ended at time 0 min and ACTH1–24 was administered at times 90 and 180 min. Plasma cortisol concentrations mate normalized concentration ranges associated with were measured in blood samples drawn 90 and 180 min after medium anesthetic depth (i.e., anesthesia score of 3), full infusion termination. n = 4 dogs for each data point. anesthetic recovery (i.e., anesthesia score of 0), and in vivo

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Fig. 8. Adrenocortical response to adrenocorticotropic hormone (ACTH) stimulation after administration of vehicle, cyclopropyl-methoxycarbonyl metomidate (CPMM), or etomidate. (A) ACTH1–24-stimulated cortisol concentrations after administering a single bolus followed by 2-h infusion of vehicle, CPMM, or etomidate. Infusions ended at time 0 min and ACTH1–24 was administered at times 0, 90, and 180 min. Plasma cortisol concentrations were measured in blood samples drawn 0, 90, and 180 min after infusion termination. The inset plots the normalized cortisol concentration drawn from CPMM and etomidate group dogs as a function of time after infusion termination. The normalized cortisol concentration was defined as the plasma cortisol concentration drawn from hypnotic group dogs normalized to that drawn from vehicle control group dogs at the same time point. The curves are fits of each data set to an exponential equation whose amplitude has been constrained to 1 (i.e., full recovery at infinite time after hypnotic administration). (B) In vivo concentration–response curves for hypnotic suppression of adrenocortical responsiveness to ACTH1–24 stimulation. The curves are nonlinear least square fits of the CPMM and etomidate data to a Hill equation. The maxima and minima for the curve fits were constrained to 1 and 0, respectively. Because there was relatively little increase in plasma cortisol concentrations after etomidate infusion within the 5-h postinfusion study period, both data sets were fit to a single Hill coefficient. The calculated 50IC s were 27 ng/ml (95% CI, 22 to 32 ng/ml) for CPMM and 16 ng/ml (95% CI, 8.5 to 30 ng/ml; P = 0.0234) for etomidate. The shared Hill coefficient was −2.0 (95% CI, −2.7 to −1.2). The shaded bars indicate the plasma hypnotic concentration range associated with anesthesia recovery. n = 4 dogs for each data point. * P < 0.05; ** P < 0.01.*** P < 0.001; and ****P < 0.0001 versus vehicle control. #P < 0.05 versus etomidate.

adrenolytic IC50 value (i.e., adrenocortical half-inhibitory of CPMM remained lower than that of etomidate (and concentration). therefore reached the adrenolytic IC50 value sooner), but After single bolus administration, the normalized the rate of decline was similar for the two drugs (half-life plasma concentration of CPMM decreased much more approximately 90 min) suggesting a common rate-con- quickly than that of etomidate (fig. 8A). Ten minutes after trolling step. Previous studies with etomidate suggest that hypnotic bolus, CPMM’s normalized concentration was this slow step is the return of drug to the central com- 33% of that of etomidate and (in contrast to etomidate) partment from a deep peripheral compartment into which below that associated with full anesthetic recovery. This drug had accumulated over time and was protected from explains why dogs emerge more quickly after a CPMM metabolism.43 bolus than after an etomidate bolus. One hour after the Similar to etomidate, CPMM produced myoclonus hypnotic bolus, CPMM’s normalized concentration was that is substantially attenuated (or eliminated) by mid- 7% of that of etomidate and (also in contrast to etomidate) azolam. The incidence of myoclonus in our dogs was well below its adrenolytic IC50 value due to its far more greater during CPMM infusion than during etomidate rapid metabolism. infusion (for all studies: 8 of 8 dogs vs. 2 of 4 dogs, respec- After single bolus followed by 2-h infusion, the normal- tively), and consequently, midazolam dosing was higher ized plasma concentration of CPMM initially decreased during the former (average midazolam dose in all stud- more quickly than that of etomidate and on the same time ies: 0.4 ± 0.15 mg/kg vs. 0.13 ± 0.15 mg/kg, respectively). scale that we had observed after single bolus administra- The higher midazolam dosing with CPMM as compared tion (fig. 8B). Thirty minutes after ending the hypnotic with etomidate (including in the behavioral recovery stud- infusion, CPMM’s normalized concentration was 13% ies) indicates that the more rapid behavioral recovery seen of etomidate’s normalized concentration and (in contrast with CPMM is not a manifestation of midazolam admin- to etomidate) below that associated with full anesthetic istration as the higher midazolam dosing is predicted to recovery. Beyond 30 min, the normalized concentration slow recovery. Rather, the significantly faster recovery after

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Fig. 9. Normalized plasma hypnotic concentrations after (A) single bolus or (B) single bolus followed by 2-h hypnotic infusion. Plasma concentrations of each hypnotic were normalized to the concentration present during medium anesthesia depth (i.e., anesthesia score 3). For single-bolus-only studies, this was the plasma hypnotic concentration 30 s after bolus administration. For single bolus followed by 2-h hypnotic infusion studies, this was the plasma hypnotic concentration when the infusion ended. The approximate relative hypnotic concentrations associated with an anesthesia score of 3, full anesthetic recovery, and adrenolytic IC50 (adrenocortical half-inhibitory concentration) are indicated by the shaded bars. CPMM = cyclopropyl-methoxycarbonyl metomidate.

CPMM administration almost certainly reflects CPMM’s venous concentrations of CPMM that are only 1/2 to 1/3 faster rate of metabolism. those of etomidate. Although we have not yet characterized the hypnotic potency of CPMM metabolite, the current studies sug- Acknowledgments gest that it may be orders of magnitude lower than that The authors thank Scott Chappel, Ph.D., Annovation Bio- of CPMM; complete hypnotic recovery occurs within Pharma, Cambridge, Massachusetts, for his helpful com- minutes of terminating a 2-h CPMM infusion even as the ments during the writing of this article, Robert J. Gutten- dorf, Ph.D., DMPK at Aclairo Pharmaceutical Development metabolite persists at a concentration (in the blood) that is Group, Vienna, Virginia, for his assistance in modeling the 10 times greater than that associated with CPMM-induced pharmacokinetic data, and T. Scott Johnson, M.D., The Med- hypnosis. Such low hypnotic potency is also predicted by icines Company, Parsippany, New Jersey, for critical reading studies showing that CPMM metabolite’s potency for of the article. enhancing γ-aminobutyric acid receptor function is less Supported by Annovation BioPharma, Inc., Cambridge, Massachusetts, and grant R01-GM087316 from the National than 1 of 1,000 that of CPMM (unpublished results, E. Institutes of Health, Bethesda, Maryland, and the Depart- Pejo and D. E. Raines, Massachusetts General Hospital, ment of Anesthesia, Critical Care, and Pain Medicine, Mas- March 2013). sachusetts General Hospital, Boston, Massachusetts. The blood samples drawn for our pharmacokinetic mea- surements were taken from the venous circulation. For drugs Competing Interests that are metabolized rapidly in the periphery (i.e., extrahe- The Massachusetts General Hospital has published and patically), concentrations measured in venous blood may be submitted patent applications for cyclopropyl-methoxycar- lower than those measured in arterial blood because signifi- bonyl metomidate and related analogues. Dr. Raines is the cant tissue metabolism occurs as the drugs transit from the lead inventor of this technology. He and his laboratory could receive compensation related to the development venous to the arterial systems. For example, remifentanil of this technology. This technology has been licensed to concentrations in the venous circulation are approximately Annovation BioPharma, Inc. (Cambridge, Massachusetts). half that of the arterial circulation during infusion.44 Such Drs. Grayzel, Pojasek, Randle, and Raines have equity in- arterial-venous concentration gradients can affect the val- terests in Annovation BioPharma, Inc. Dr. Campagna is an ues of pharmacokinetic and pharmacodynamic parameters employee of The Medicines Company (Parsippany, New Jersey), which has an equity interest in Annovation Bio- derived from modeling, including increasing the calculated Pharma, Inc. clearance and steady-state volume of distribution. In our data set, this gradient may also explain why the extrapolated Correspondence initial concentration (C ) of CPMM in our bolus studies 0 Address correspondence to Dr. Raines: Department of Anes- was only half that of etomidate even though the CPMM thesia, Critical Care, and Pain Medicine, Massachusetts Gen- dose was higher. It may also explain why the same level eral Hospital, 55 Fruit Street, GRB444, Boston, Massachusetts of anesthetic depth was reached in our bolus studies with 02114. [email protected]. Information on purchasing re-

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37. Davies B, Morris T: Physiological parameters in laboratory 41. lambert A, Mitchell R, Robertson WR: Effect of propofol, animals and humans. Pharm Res 1993; 10:1093–5 thiopentone and etomidate on adrenal steroidogenesis in 38. Fraser R, Watt I, Gray CE, Ledingham IM, Lever AF: The vitro. Br J Anaesth 1985; 57:505–8 effect of etomidate on adrenocortical function in dogs 42. Crozier TA, Beck D, Wuttke W, Kettler D: [Relation of the before and during hemorrhagic shock. Endocrinology 1984; inhibition of cortisol synthesis in vivo to plasma etomidate 115:2266–70 concentrations]. Anaesthesist 1988; 37:337–9 39. Kruse-Elliott KT, Swanson CR, Aucoin DP: Effects of etomi- 43. Van Hamme MJ, Ghoneim MM, Ambre JJ: Pharmacokinetics date on adrenocortical function in canine surgical patients. of etomidate, a new intravenous anesthetic. Anesthesiology Am J Vet Res 1987; 48:1098–100 1978; 49:274–7 40. Dodam JR, Kruse-Elliott KT, Aucoin DP, Swanson CR: 44. hermann DJ, Egan TD, Muir KT: Influence of arteriovenous Duration of etomidate-induced adrenocortical suppression sampling on remifentanil pharmacokinetics and pharmaco- during surgery in dogs. Am J Vet Res 1990; 51:786–8 dynamics. Clin Pharmacol Ther 1999; 65:511–8 Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/121/6/1203/485458/20141200_0-00019.pdf by guest on 29 September 2021

ANESTHESIOLOGY REFLECTIONS FROM THE WOOD LIBRARY-MUSEUM

Parke-Davis Medicated Throat Discs: Chloroforming That Throat “Tickle”

Formulated with capsicum, peppermint, anise, cubeb, licorice, linseed, acacia, and sugar, each Parke-Davis Medicated Throat Disc included 0.5 minim or roughly 0.03 ml of chloroform (lower right). This half-drop of chloroform provided some topical relief but also served as a solvent for the other “herbs and spices.” Targeting “singers, speakers, and smokers,” the box (upper left) for these throat discs promised relief from “coughs due to colds, hoarseness, and that annoying ‘tickle’ in the throat.” By 1976, the Food and Drug Administration was directing that all drugs containing chloroform be removed from sale, so this particular formulation … evaporated. (Copyright © the American Society of Anesthesiologists, Inc.) George S. Bause, M.D., M.P.H., Honorary Curator, ASA’s Wood Library-Museum of Anesthesiology, Schaumburg, Illinois, and Clinical Associate Professor, Case Western Reserve University, Cleveland, Ohio. [email protected].

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