Interactions between calcium entry blockers and vecuronium bromide in anaesthetized cats

Possible interactions between three calcium entry blocking agents (nifedipine, verapamil and bepridil) and the non-depolarizing neuromuscular blocking agent, vecuronium bromide, were investigated in chloralose-anaesthetized cats. In i.v. doses which caused decreases in arterial pressure, the calcium entry blockers did not affect indirectly-elicited twitches of tibialis muscle, but did potentiate the effects of vecuronium. No such potentiation of vecuronium was observed with the vasodilator drug, sodium nitroprusside. Experiments using close-arterial injections of acetylcholine suggested that the probable site of interaction is on the postsynaptic muscle membrane and probably involves blockade of calcium channels in skeletal muscle.