In vitro study of interactions between i.v. anaesthetics and neuromuscular blocking agents.

The interactions of four anaesthetic drugs (ketamine, propanidid, Althesin and methohexitone) with two neuromuscular blocking agents (suxamethonium and pancuronium) have been investigated. On the isolated rat phrenic nerve-diaphragm preparation, all the anaesthetic drugs examined potentiated suxamethonium more than they potentiated pancuronium. The anticholinesterase agent, ecothiopate, had no significant effect on the potentiation of suxamethonium caused by the anaesthetic drugs. At low concentrations the anaesthetic drugs increased the twitch tension elicited by stimulation of the phrenic nerve, whilst at high concentrations this potentiation was followed by blockade of neuromuscular transmission. With the exception of Althesin, all the anaesthetics decreased the sensitivity of the frog rectus preparation to acetylcholine. The possible sites and mechanisms of these interactions are discussed.