Protection from Digitalis Toxicity with the Prophylactic Use of Diphenylhydantoin Sodium

Diphenylhydantoin sodium (Dilantin) given prophylactically increased the dose of digitalis necessary to produce toxicity by 72 to 224%. At constant heart rates, pretreatment with diphenylhydantoin sodium did not alter the elevation of rate of rise of left ventricular pressure produced by the glycoside. Two implications have been drawn from these findings. First, the inotropic and arrhythmic actions of digitalis can be dissociated, since diphenylhydantoin sodium seems specifically to counteract the electrophysiological actions of the glycoside. Second, pretreatment with diphenylhydantoin sodium significantly widened the "toxic-therapeutic" ratio of digitalis. This, therefore, may have important clinical applications.