This drug should be administered only by adequately trained individuals familiar with its actions, characteristics, and hazards.

NOT FOR USE IN NEONATES

CONTAINS BENZYL ALCOHOL

DESCRIPTION

MIVACRON (mivacurium chloride) is a short-acting, nondepolarizing skeletal muscle relaxant for intravenous (IV) administration. Mivacurium chloride is [R-[R*,R*-(E)]]-2,2'-[(1,8-dioxo-4-octene-1,8-diyl)bis(oxy-3,1-propanediyl)]bis[1,2,3,4-tetrahydro-6,7-dimethoxy-2-methyl-1-[(3,4,5-trimethoxyphenyl)methyl]isoquinolinium] dichloride. The molecular formula is C58H80Cl2N2O14 and the molecular weight is 1100.18. The structural formula is:

The partition coefficient of the compound is 0.015 in a 1-octanol/distilled water system at 25°C.

Mivacurium chloride is a mixture of three stereoisomers: (1R,1'R , 2S, 2'S ), the trans-trans diester; (1R,1'R , 2R, 2'S ), the cis-trans diester; and (1R,1'R , 2R, 2'R ), the cis-cis diester. The trans-trans and cis-trans stereoisomers comprise 92% to 96% of mivacurium chloride and their neuromuscular blocking potencies are not significantly different from each other or from mivacurium chloride. The cis-cis diester has been estimated from studies in cats to have one-tenth the neuromuscular blocking potency of the other two stereoisomers.

MIVACRON Injection is a sterile, non-pyrogenic solution (pH 3.5 to 5.0) containing mivacurium chloride equivalent to 2 mg/mL mivacurium in Water for Injection. Hydrochloric acid may have been added to adjust pH. Multiple-dose vials contain 0.9% w/v benzyl alcohol.

CLINICAL PHARMACOLOGY

MIVACRON (a mixture of three stereoisomers) binds competitively to cholinergic receptors on the motor end-plate to antagonize the action of acetylcholine, resulting in a block of neuromuscular transmission. This action is antagonized by acetylcholinesterase inhibitors, such as neostigmine.

Pharmacodynamics

The time to maximum neuromuscular block is similar for recommended doses of MIVACRON and intermediate-acting agents (e.g., atracurium), but longer than for the ultra-short-acting agent, succinylcholine. The clinically effective duration of action of MIVACRON (a mixture of three stereoisomers) is one-third to one-half that of intermediate-acting agents and 2 to 2.5 times that of succinylcholine.

The average ED95 (dose required to produce 95% suppression of the adductor pollicis muscle twitch response to ulnar nerve stimulation) of MIVACRON is 0.07 mg/kg (range:  0.05 to 0.09) in adults receiving opioid/nitrous oxide/oxygen anesthesia. The pharmacodynamics of doses of MIVACRON ≥ ED95 administered over 5 to 15 seconds during opioid/nitrous oxide/oxygen anesthesia are summarized in Table 1. The mean time for spontaneous recovery of the twitch response from 25% to 75% of control amplitude is about 6 minutes (range: 3 to 9, n = 32) following an initial dose of 0.15 mg/kg MIVACRON and 7 to 8 minutes (range: 4 to 24, n = 85) following initial doses of 0.20 or 0.25 mg/kg MIVACRON.

Volatile anesthetics may decrease the dosing requirement for MIVACRON and prolong the duration of action; the magnitude of these effects may be increased as the concentration of the volatile agent is increased. Isoflurane and enflurane (administered with nitrous oxide/oxygen to achieve 1.25 MAC [Minimum Alveolar Concentration]) may decrease the effective dose of MIVACRON by as much as 25%, and may prolong the clinically effective duration of action and decrease the average infusion requirement by as much as 35% to 40%. At equivalent MAC values, halothane has little or no effect on the ED50 of MIVACRON, but may prolong the duration of action and decrease the average infusion requirement by as much as 20% (see CLINICAL PHARMACOLOGY - Individualization of Dosages subsection and PRECAUTIONS - Drug Interactions).

Administration of MIVACRON over 30 to 60 seconds does not alter the time to maximum neuromuscular block or the duration of action. The duration of action of MIVACRON may be prolonged in patients with reduced plasma cholinesterase (pseudocholinesterase) activity (see PRECAUTIONS - Reduced Plasma Cholinesterase Activity and CLINICAL PHARMACOLOGY - Individualization of Dosages subsection).

Interpatient variability in duration of action occurs with MIVACRON as with other neuromuscular blocking agents. However, analysis of data from 224 patients in clinical studies receiving various doses of MIVACRON during opioid/nitrous oxide/oxygen anesthesia with a variety of premedicants and varying lengths of surgery indicated that approximately 90% of the patients had clinically effective durations of block within 8 minutes of the median duration predicted from the dose-response data shown in Table 1. Variations in plasma cholinesterase activity, including values within the normal range and values as low as 20% below the lower limit of the normal range, were not associated with clinically significant effects on duration. The variability in duration, however, was greater in patients with plasma cholinesterase activity at or slightly below the lower limit of the normal range.

When administered during the induction of adequate anesthesia using thiopental or propofol, nitrous oxide/oxygen, and co-induction agents such as fentanyl and/or midazolam, doses of 0.15 mg/kg (2 x ED95) MIVACRON administered over 5 to 15 seconds or 0.20 mg/kg MIVACRON administered over 30 seconds produced generally good-to-excellent tracheal intubation conditions in 2.5 to 3 and 2 to 2.5 minutes, respectively. A dose of 0.25 mg/kg MIVACRON administered as a divided dose (0.15 mg/kg followed 30 seconds later by 0.10 mg/kg) produced generally good-to-excellent intubation conditions in 1.5 to 2 minutes after initiating the dosing regimen.

Repeated administration of maintenance doses or continuous infusion of MIVACRON for up to 2.5 hours is not associated with development of tachyphylaxis or cumulative neuromuscular blocking effects in ASA Physical Status I-II patients. Based on pharmacokinetic studies in 82 adults receiving infusions of MIVACRON for longer than 2.5 hours, spontaneous recovery of neuromuscular function after infusion is independent of the duration of infusion and comparable to recovery reported for single doses (Table 1).

MIVACRON was administered as an infusion for as long as 4 to 6 hours in 20 adult patients and 19 geriatric patients. In most patients, after a brief period of adjustment, the rate of MIVACRON required to maintain 89% to 99% T1 suppression remained relatively constant over time. There was a subset of patients in each group whose infusion rates did not stabilize quickly and decreased (by ≥ 30%) over the period of infusion. The rate of spontaneous recovery in these patients was comparable with that of patients having stable infusion rates and not dependent on the duration of infusion. These patients, however, tended to have higher infusion requirements (i.e., > 8 mcg/kg/min) during the first 30 minutes of infusion than patients with stable infusion rates, although their final infusion rates were similar to those with stable infusion rates. There were no clinically important differences in infusion rate requirements between geriatric and young patients (see Pharmacokinetics -Special Populations - Geriatric Patients ).

The neuromuscular block produced by MIVACRON is readily antagonized by anticholinesterase agents. As seen with other nondepolarizing neuromuscular blocking agents, the more profound the neuromuscular block at the time of reversal, the longer the time and the greater the dose of anticholinesterase agent required for recovery of neuromuscular function.

In children (2 to 12 years), MIVACRON has a higher ED95 (0.10 mg/kg), faster onset, and shorter duration of action than in adults. The mean time for spontaneous recovery of the twitch response from 25% to 75% of control amplitude is about 5 minutes (n = 4) following an initial dose of 0.20 mg/kg MIVACRON. Recovery following reversal is faster in children than in adults (Table 1).

Hemodynamics

Administration of MIVACRON in doses up to and including 0.15 mg/kg (2 x ED95) over 5 to 15 seconds to ASA Physical Status I-II patients during opioid/nitrous oxide/oxygen anesthesia is associated with minimal changes in mean arterial blood pressure (MAP) or heart rate (HR) (Table 2).

Higher doses of ≥ 0.20 mg/kg (≥ 3 x ED95) may be associated with transient decreases in MAP and increases in HR in some patients. These decreases in MAP are usually maximal within 1 to 3 minutes following the dose, typically resolve without treatment in an additional 1 to 3 minutes, and are usually associated with increases in plasma histamine concentration. Decreases in MAP can be minimized by administering MIVACRON over 30 to 60 seconds (see CLINICAL PHARMACOLOGY - Individualization of Dosages subsection and PRECAUTIONS - General).

Analysis of 426 patients in clinical studies receiving initial doses of MIVACRON up to and including 0.30 mg/kg during opioid/nitrous oxide/oxygen anesthesia showed that high initial doses and a rapid rate of injection contributed to a greater probability of experiencing a decrease of ≥ 30% in MAP after administration of MIVACRON. Obese patients also had a greater probability of experiencing a decrease of ≥ 30% in MAP when dosed on the basis of actual body weight, thereby receiving a larger dose than if dosed on the basis of ideal body weight (see CLINICAL PHARMACOLOGY - Individualization of Dosages subsection and PRECAUTIONS - General ).

Children experience minimal changes in MAP or HR after administration of doses of MIVACRON up to and including 0.20 mg/kg over 5 to 15 seconds, but higher doses (≥ 0.25 mg/kg) may be associated with transient decreases in MAP (Table 2).

Following a dose of 0.15 mg/kg MIVACRON administered over 60 seconds, adult patients with significant cardiovascular disease undergoing coronary artery bypass grafting or valve replacement procedures showed no clinically important changes in MAP or HR. Transient decreases in MAP were observed in some patients after doses of 0.20 to 0.25 mg/kg MIVACRON administered over 60 seconds. The number of patients in whom these decreases in MAP required treatment was small.

Pharmacokinetics

MIVACRON is a mixture of isomers which do not interconvert in vivo. The cis-trans and trans-trans isomers (92% to 96% of the mixture) are equipotent. The steady-state concentrations of the cis-trans and trans-trans isomers doubled after the infusion rate was increased from 5 to 10 mcg/kg/min, indicating that their pharmacokinetics is dose-proportional.

The cis-cis isomer (6% of the mixture) has approximately one-tenth the neuromuscular blocking potency of the trans-trans and cis-trans isomers in cats. Neuromuscular blocking effects due to the cis-cis isomer cannot be ruled out in humans; however, modeling of clinical pharmacokinetic-pharmacodynamic data suggests that the cis-cis isomer produces minimal (< 5%) neuromuscular block during a 2-hour infusion. In studies of ASA Physical Status I-II patients receiving infusions of MIVACRON lasting as long as 4 to 6 hours, the 5% to 25% and the 25% to 75% recovery indices were independent of the duration of infusion, suggesting that the cis-cis isomer does not affect the rate of post-infusion recovery.

Distribution

The volume of distribution of cis-trans and trans-trans isomers in healthy surgical patients is relatively small, reflecting limited tissue distribution (Table 3). The volume of distribution of cis-cis isomers is also small and averaged 335 mL/kg (range 192 to 523) in the 18 healthy surgical patients whose data are displayed in Table 3. The protein binding of mivacurium has not been determined due to its rapid hydrolysis by plasma cholinesterase.

Metabolism

Enzymatic hydrolysis by plasma cholinesterase is the primary mechanism for inactivation of mivacurium and yields a quaternary alcohol and a quaternary monoester metabolite. Tests in which these two metabolites were administered to cats and dogs suggest that each metabolite is unlikely to produce clinically significant neuromuscular, autonomic, or cardiovascular effects following administration of MIVACRON.

The mean ± S.D. in vitro t½ values of the trans-trans and the cis-trans isomers were 1.3 ± 0.3 and 0.8 ± 0.2 minutes, respectively, in human plasma from healthy male (n = 5) and female (n = 5) volunteers. The mean in vivo t½ values for the more potent trans-trans and cis-trans isomers in healthy surgical patients (Table 3) were similar to those found in vitro , suggesting that hydrolysis by plasma cholinesterase is the predominant elimination pathway for these isomers. The mean ± S.D. in vitro t½ of the less potent cis-cis isomer was 276 ± 130 minutes, while the mean ± S.D. in vivo t½ for the cis-cis isomer in healthy surgical patients was 53 ± 20 minutes. These data suggest that in vivo , pathways other than hydrolysis by plasma cholinesterase contribute to the elimination of the cis-cis isomer.

Elimination

The clearance (CL) values of the two more potent isomers, cis-trans and trans-trans , are very high and are dependent on plasma cholinesterase activity (Table 3). The combination of high CL and low distribution volume results in t½ values of approximately 2 minutes for the two more potent isomers. The short t½ and high CL of the more potent isomers are consistent with the short duration of action of MIVACRON.

The CL of the less potent cis-cis isomer is not dependent on plasma cholinesterase. The mean ± S.D. CL was 4.6 ± 1.1 mL/min/kg and t½ was 53 ± 20 minutes in the 18 healthy surgical patients whose data are displayed in Table 3.

Renal and biliary excretion of unchanged mivacurium are minor elimination pathways; urine and bile are important elimination pathways for the two metabolites.

Special Populations

Geriatric Patients (≥ 60 years)

Two pharmacokinetic/pharmacodynamic studies of MIVACRON have been conducted in geriatric patients. The first study compared the pharmacokinetics and pharmacodynamics of mivacurium in 19 geriatric patients with those in 20 adult patients receiving infusions for as long as 4 to 6 hours. The average infusion rate required to produce 89% to 99% T1 suppression was slightly (~ 14%) lower in geriatric patients. This difference is not regarded as clinically important, but is most likely secondary to differences in pharmacokinetics (i.e., a lower CL of the cis-trans and trans-trans isomers in geriatric patients) (Table 4). The rate of post-infusion spontaneous recovery was not dependent on duration of infusion and appeared to be comparable in these geriatric patients and adult patients. Two pharmacodynamic studies in which patients received infusions for a shorter duration (2 to 3 hours) have shown that the infusion rate requirements were lower (by 38%) in geriatric patients (64 to 86 years of age) than in younger patients (18 to 41 years of age).

The second pharmacokinetic/pharmacodynamic study showed no clinically important differences in the pharmacokinetics of the individual isomers nor the ED95 determined for 36 young adult patients (18 to 40 years) and 35 geriatric patients (≥ 65 years) during opioid/nitrous oxide/oxygen anesthesia. Following infusions for up to 3.5 hours in these patients, the rate of spontaneous recovery was slightly (~ 2 to 4 minutes, on average) slower in the geriatric patients than in young adult patients.

In a third study of the pharmacodynamics of 0.1 mg/kg MIVACRON administered to eight geriatric patients (68 to 77 years) and nine adult patients (18 to 49 years) during N2O/O2/isoflurane anesthesia, the time to onset was approximately 1.5 minutes slower in geriatric patients than in adult patients. In addition, the clinical duration was slightly (~ 3 minutes, on average) longer in geriatric patients than in adult patients; these differences are not considered clinically important.

Although these studies showed conflicting findings, in general, the clearances of the more potent isomers are most likely lower in geriatric patients. This difference does not lead to clinically important differences in the ED95 of MIVACRON or the infusion rate of MIVACRON required to produce 95% T1 suppression in geriatric patients. However, the time to onset may be slower, the duration may be slightly longer, the rate of recovery may be slightly slower, therefore MIVACRON requirements may be lower in geriatric patients.

Patients with Renal Disease

An early clinical trial showed that the clinically effective duration of action of 0.15 mg/kg MIVACRON was about 1.5 times longer in kidney transplant patients than in healthy patients, presumably due to reduced clearance of one or more isomers. A second study was conducted in seven patients with mild to moderate renal impairment, eight patients with severe renal dysfunction (not undergoing transplantation), and 11 patients with normal renal function. This study showed that the pharmacokinetics of the more potent (cis-trans and trans-trans) isomers were not statistically significantly affected by renal impairment or failure (Table 5). However, the CL of the cis-cis isomer was lower and the t½ values of the cis-cis isomer and metabolites were longer in patients with renal impairment or failure than in patients with normal renal function. The second study also showed that there were no differences in the average infusion rate required to produce 89% to 99% T1 suppression, nor were there any differences in the post-infusion recovery profile among these populations (Table 5). A third study in a similar population showed that patients with renal dysfunction had a longer duration and a slower rate of recovery than patients with normal renal function. This study did, however, confirm that there were no differences in the average infusion rate required to produce 89% to 99% T1 suppression in these patient populations. Therefore, although there were minor differences in the pharmacokinetics of the cis-cis isomer and metabolites, there were no clinically significant differences in the infusion rate requirements of MIVACRON in patients with mild, moderate, or severe renal dysfunction receiving infusions of MIVACRON for an average of 1 to 2 hours; however, the duration may be longer and the rate of recovery may be slower following administration of MIVACRON in some patients with renal dysfunction.

Patients with Hepatic Disease

The clinically effective duration of action of 0.15 mg/kg MIVACRON was three times longer in eight patients with end-stage liver disease (undergoing liver transplantation) than in eight healthy patients and is likely related to the markedly decreased plasma cholinesterase activity (30% of healthy patient values) which could decrease the clearance of the trans-trans and cis-trans isomers (see PRECAUTIONS - Reduced Plasma Cholinesterase Activity).

A separate study compared the pharmacokinetics and pharmacodynamics of mivacurium in patients with mild or moderate cirrhosis to healthy adults with normal hepatic function (Table 6). Although the number of patients in each group is small, the CL values of the more potent isomers, trans-trans and cis-trans, are lower in patients with mild to moderate cirrhosis as expected based on the marked decreases in plasma cholinesterase activity in this population (see PRECAUTIONS - Reduced Plasma Cholinesterase Activity).

Individualization of Dosages

DOSES OF MIVACRON SHOULD BE INDIVIDUALIZED AND A PERIPHERAL NERVE STIMULATOR SHOULD BE USED TO MEASURE NEUROMUSCULAR FUNCTION DURING ADMINISTRATION OF MIVACRON IN ORDER TO MONITOR DRUG EFFECT, DETERMINE THE NEED FOR ADDITIONAL DOSES, AND CONFIRM RECOVERY FROM NEUROMUSCULAR BLOCK.

Based on the known actions of MIVACRON (a mixture of three stereoisomers) and other neuromuscular blocking agents, the following factors should be considered when administering MIVACRON:

Renal or Hepatic Impairment

A dose of 0.15 mg/kg MIVACRON is recommended for facilitation of tracheal intubation in patients with renal or hepatic impairment. However, the clinically effective duration of block produced by this dose may be about 1.5 times longer in patients with end-stage kidney disease and about 3 times longer in patients with end-stage liver disease than in patients with normal renal and hepatic function. Infusion rates should be decreased by as much as 50% in patients with hepatic disease depending on the degree of hepatic impairment (see PRECAUTIONS - Renal and Hepatic Disease). No infusion rate adjustments are necessary in patients with renal impairment.

Reduced Plasma Cholinesterase Activity

The possibility of prolonged neuromuscular block following administration of MIVACRON must be considered in patients with reduced plasma cholinesterase (pseudocholinesterase) activity. MIVACRON should be used with great caution, if at all, in patients known or suspected of being homozygous for the atypical plasma cholinesterase gene (see WARNINGS ). Doses of 0.03 mg/kg produced complete neuromuscular block for 26 to 128 minutes in three such patients; thus initial doses greater than 0.03 mg/kg are not recommended in homozygous patients. Infusions of MIVACRON are not recommended in homozygous patients.

MIVACRON has been used safely in patients heterozygous for the atypical plasma cholinesterase gene and in genotypically normal patients with reduced plasma cholinesterase activity. After an initial dose of 0.15 mg/kg MIVACRON, the clinically effective duration of block in heterozygous patients may be approximately 10 minutes longer than in patients with normal genotype and normal plasma cholinesterase activity. Lower infusion rates of MIVACRON are recommended in these patients (see PRECAUTIONS - Reduced Plasma Cholinesterase Activity).

Drugs or Conditions Causing Potentiation of or Resistance to Neuromuscular Block

As with other neuromuscular blocking agents, MIVACRON may have profound neuromuscular blocking effects in cachectic or debilitated patients, patients with neuromuscular diseases, and patients with carcinomatosis. In these or other patients in whom potentiation of neuromuscular block or difficulty with reversal may be anticipated, the initial dose should be decreased. A test dose of not more than 0.015 to 0.020 mg/kg, which represents the lower end of the dose-response curve for MIVACRON, is recommended in such patients (see PRECAUTIONS - General).

The neuromuscular blocking action of MIVACRON is potentiated by isoflurane or enflurane anesthesia. Recommended initial doses of MIVACRON (see DOSAGE AND ADMINISTRATION) may be used for intubation prior to the administration of these agents. If MIVACRON is first administered after establishment of stable-state isoflurane or enflurane anesthesia (administered with nitrous oxide/oxygen to achieve 1.25 MAC), the initial dose of MIVACRON should be reduced by as much as 25%, and the infusion rate reduced by as much as 35% to 40%. A greater potentiation of the neuromuscular blocking action of MIVACRON may be expected with higher concentrations of enflurane or isoflurane. The use of halothane requires no adjustment of the initial dose of MIVACRON, but may prolong the duration of action and decrease the average infusion rate by as much as 20% (see PRECAUTIONS - Drug Interactions).

When MIVACRON is administered to patients receiving certain antibiotics, magnesium salts, lithium, local anesthetics, procainamide and quinidine, longer durations of neuromuscular block may be expected and infusion requirements may be lower (see PRECAUTIONS - Drug Interactions).

When MIVACRON is administered to patients chronically receiving phenytoin or carbamazepine, slightly shorter durations of neuromuscular block may be anticipated and infusion rate requirements may be higher (see PRECAUTIONS - Drug Interactions).

Severe acid-base and/or electrolyte abnormalities may potentiate or cause resistance to the neuromuscular blocking action of MIVACRON. No data are available in such patients and no dosing recommendations can be made (see PRECAUTIONS - General).

Burns

While patients with burns are known to develop resistance to nondepolarizing neuromuscular blocking agents, they may also have reduced plasma cholinesterase activity. Consequently, in these patients, a test dose of not more than 0.015 to 0.020 mg/kg MIVACRON is recommended, followed by additional appropriate dosing guided by the use of a neuromuscular block monitor (see PRECAUTIONS - General).

Cardiovascular Disease

In patients with clinically significant cardiovascular disease, the initial dose of MIVACRON should be 0.15 mg/kg or less, administered over 60 seconds (see CLINICAL PHARMACOLOGY - Hemodynamics subsection and PRECAUTIONS - General ).

Obesity

Obese patients (patients weighing ≥ 30% more than their ideal body weight) dosed on the basis of actual body weight, thereby receiving a larger dose than if dosed on the basis of ideal body weight, had a greater probability of experiencing a decrease of ≥ 30% in MAP (see CLINICAL PHARMACOLOGY - Hemodynamics subsection and PRECAUTIONS - General). Therefore, in obese patients, the initial dose should be determined using the patient's ideal body weight (IBW), according to the following formulae:

Allergy and Sensitivity

In patients with any history suggestive of a greater sensitivity to the release of histamine or related mediators (e.g., asthma), the initial dose of MIVACRON should be 0.15 mg/kg or less, administered over 60 seconds (see PRECAUTIONS - General).

INDICATIONS AND USAGE

MIVACRON is a short-acting neuromuscular blocking agent indicated for inpatients and outpatients, as an adjunct to general anesthesia, to facilitate tracheal intubation and to provide skeletal muscle relaxation during surg