Neuromuscular blockers Carbamazepine

D. Anticonvulsants (carbamazepine and phenytoin) and theophylline may delay the onset and shorten the duration of action of some nondepolarizing agents. Carbamazepine has additive effects, and reduction of the neuromuscular blocker dose may be required. 

The effects of many competitive neuromuscular blockers are reduced and shortened if carbamazepine or phenytoin are given for longer than one week, but they appear to be increased if phenytoin, and possibly carbamazepine, are given acutely (e.g. during surgery). Carbamazepine and phenytoin appear not to interact with mivacurium. 

An in vitro study found that the acute neuromuscular effects of carbamazepine reduced the concentrations required for 50% paralysis with both a depolarising neuromuscular blocker (suxamethonium (succinylcholine)) and a competitive neuromuscular blocker (atracurium) by about 30%. ... 

Anticipate the need to use a smaller neuromuscular blocker dosage, or prepare for a longer recovery time if phenytoin and possibly carbamazepine are given acutely. 

Drug Interactions Other antihypertensive agents Carbamazepine (vasodilators, ACE inhibitors, Rifampin diuretics, and beta-blockers) Phenobarbital Digoxin Cyclosporine Disopyramide Theophylline Flecainide Inhalation anesthetics Quinidine Neuromuscular blocking agents Cimetidine Lithium ... 

Not fully understood, but it appears to be multifactorial. Acute administration of phenytoin or carbamazepine may result in neuromuscular block and potentiation of the action of competitive (non-depolarising) blockers. ... 

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