The Clinical Neuromuscular Pharmacology of Mivacurium Chloride (BW B1090U). A Short-acting Nondepolarizing Ester Neuromuscular Blocking Drug

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Abstract

Mivacurium chloride (BW B1090U), a bis-benzylisoquinolinium diester compound, was found to undergo hydrolysis in vitro by purified human plasma cholinesterase in a pH-stat titralorat 88% of the rate of succinylcholine at pH 7.4,37°C and 5 μM substrate concentration. In 72 consenting ASA Physical Status I-II patients receiving nitrous oxide/oxygen-narcotic-thiopental anesthesia, the neuromuscular blocking effect of mivacurium was assessed following bolus doses from 0.03 to 0.30 mg/kg, as well as during and following continuous infusions from 35 to 324 min in length. The calculated ED95 for inhibition of adductor pollicis twitch evoked at 0.15 Hz was 0.08 mg/kg. At 0.1 mg/kg, 96% block developed, onset to maximum block required 3.8 ± 0.5 min, and recovery to 95% twitch height occurred 24.5 ± 1.6 (SE) min after injection. At 0.25 mg/kg, onset was 2.3 ± 0.3 min; 95% recovery developed within 30.4 ± 2.2 min, an increase in duration of action of only 24% versus 150% higher dosage. Comparative recovery indices from 5 to 95% or from 25 to 75% twitch heights did not differ significantly among all dosage groups from 0.1 to 0.3 mg/kg (range 12.9 to 14.7 and 6.6 to 7.2 min, respectively). In 38 patients who received mivacurium by continuous infusion (duration 88.1 ± 7.1/47.1 min, SE/SD) for maintenance of 95 ± 4% twitch inhibition, the mean 5–95% and 25–75% recovery indices after discontinuation of infusion were 14.4 ± 0.6 and 6.5 ± 0.3 min (P > 0.5 vs. all single bolus doses). The train-of-four (T4) ratio, within 2.6 ± 0.5 min after 95% twitch recovery following bolus doses, averaged 79.5 ± 1.8% (n = 32). Similarly, after discontinuation of infusions, the T4 ratio reached 73.4 ± 1.9% within 3.4 ± 1.9 min after 95% twitch recovery (n = 33). Antagonism of residual block was seldom indicated, but, to test case of reverals, eight patients electively received ncostigmine (0.06 mg/kg) with atropine (0.03 mg/kg) at 67 to 93 (76.6 ± 3.5) % block. Twitch returned to 95% of control within 4.5 to 9.5 (6.3 ± 0.5) min after neostigmine. Mivacurium may offer increased versatility in providing clinical muscle relaxation in a variety of situations. Further studies seem appropriate.

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