“A few drugs may diminish the effects of a nondepolarizing NMBD, including calcium, corticosteroids, and anticonvulsant (phenytoin) drugs.” – Stoelting (Basics of Anesthesia) p143
Interesting, if phenytoin is acutely administered to a phenytoin-naive patient, phenytoin will potentiate the effect of neuromuscular blockade; however, if the patient is on chronic phenytoin, neuromuscular blockers will have a decreased effect.
Anouk Richard, François Girard, Dominique C Girard, Daniel Boudreault, Philippe Chouinard, Robert Moumdjian, Alain Bouthilier, Monique Ruel, Johanne Couture, France Varin Cisatracurium-induced neuromuscular blockade is affected by chronic phenytoin or carbamazepine treatment in neurosurgical patients. Anesth. Analg.: 2005, 100(2);538-44