Potentiation of Neuromuscular Blockade by Verapamil

Abstract

The effects of i.v. verapamil [VER, a Ca entry blocker] (0.01 to 1.0 mg/kg) on the constant neuromuscular block produced by an i.v. infusion of either pancuronium or succinylcholine were studied on the indirectly stimulated gastrocnemius and tibialis-anterior muscles of the rabbit anesthetized with halothane in O2. VER alone (n = 6) had no significant effect, but it did significantly potentiate the 50% twitch depression of the gastrocnemius muscle produced by a constant i.v. infusion of either pancuronium (n = 5) or succinylcholine (n = 5) to 36 .+-. 6 and 45 .+-. 1% of control, respectively. This effect of VER occurred with doses of 0.1 mg/kg for pancuronium and 0.01 mg/kg for succinylcholine; these doses of VER were the lowest which produced a significant effect. VER had no significant effect on the progression of the neuromuscular blockade of either the gastrocnemius or tibialis-anterior muscles produced by .alpha.-bungarotoxin (n = 5). VER significantly prolonged the P-R interval of the ECG from a control value of 71 .+-. 2 to 78 .+-. 3 ms at a dose of 0.1 mg/kg and to 93 .+-. 6 ms at a dose of 0.3 mg/kg. The possible mechanisms of the neuromuscular actions of VER are discussed; VER apparently can produce potentiation of either pancuronium- or succinylcholine-induced neuromuscular block at doses within the therapeutic range.