Clinical pharmacology of mivacurium chloride: a review

Mivacurium chloride (Mivacron) is a new benzylisoquinolinium choline-like diester neuromuscular blocking drug with an onset of action at equipotent doses that is comparable to atracurium and vecuronium but slower than succinylcholine. Its clinical duration (injection-25% recovery and injection-95% recovery) is twice that of succinylcholine but one-half to one-third that of atracurium and vecuronium. Mivacurium is easy to use as a continuous infusion and when used this way its recovery characteristics are unchanged. It is readily antagonized by anticholinesterase drugs. The ED95 in adults under narcotic-based anesthesia is 0.07-0.08 mg/kg. At twice the ED95 (0.15 mg/kg) onset time is about 2 to 3 minutes, duration to 25% recovery is 15 to 20 minutes, and 5-95% recovery time about 14 minutes. The mean infusion rate in adults is 6 micrograms/kg/min (range 2-15) with a 5-95% recovery time of 14 minutes. Enflurane and isoflurane require a 20-30% decrease in dosage; halothane, enflurane, and isoflurane prolong the duration of mivacurium 25-30%. The ED95 in children 2 to 12 years of age is slightly higher (0.09-0.11 mg/kg) with a faster onset and shorter duration. In these young patients, a dose of 0.2 mg/kg has an onset comparable to succinylcholine. Being chemically related to atracurium, mivacurium may cause histamine release. When administered rapidly at doses of 0.2 mg/kg or greater in adults, histamine release and transient hypotension have been observed. Doses of 0.2 mg/kg or higher are not recommended by the manufacturer. Mivacurium is metabolized by plasma cholinesterase. In vitro, the rate is about 70% that of succinylcholine. In patients with normal or slightly less than normal plasma cholinesterase activity, no prolonged durations of action have been observed. In patients heterozygous for the atypical gene and at a dose of 0.2 mg/kg, 50% prolongation has been shown. Those individuals homozygous for the atypical gene are exquisitely sensitive to mivacurium and have a markedly prolonged blockade that is readily reversible. In these patients and those with acquired deficiencies, mivacurium should not be used. The duration of action in elderly patients is comparable to that in the young, while in prerenal transplant patients, its duration is prolonged by about 50%, and in prehepatic transplant patients, duration of block is increased threefold. Mivacurium possesses the advantages of short duration, unchanged recovery characteristics following infusions (without phase II block or tachyphylaxis), and precise control.(ABSTRACT TRUNCATED AT 250 WORDS)