076 Antiarrhythmic Properties of Phenytoin: A Systematic Review

Abstract

Phenytoin has long been used to treat epilepsy and for some time as an antiarrhythmic drug (AAD). It is known that the diastolic calcium leakage through dysfunctional cardiac ryanodine receptors (RyR2) is a mechanism for arrhythmias in heart failure. Recent evidence suggests that phenytoin inhibits dysfunctional RyR2, reduces the calcium leak during diastole in heart failure, and may improve cardiac systolic function. A systematic search of MEDLINE, Embase, and the Cochrane Library databases was performed in March 2019. The search was limited to the studies published in the English language from 1946 to 2019. Studies on the antiarrhythmic effects of phenytoin in adults compared to no treatment or other AADs were included. Studies were excluded if there was insufficient clinical data regarding antiarrhythmic effects, dosing and administration of phenytoin and other ADDs. A total of 157 non-duplicate titles were screened, and 25 articles underwent full-text review. 13 studies met the inclusion criteria, representing a total of 985 patients. Phenytoin was found to be effective in treating arrhythmias associated with digitalis toxicity, and in suppressing premature ventricular contractions (PVCs).In a recent animal study, phenytoin inhibited diastolic calcium leak through dysfunctional RyR2, and improved cardiac systolic function without affecting normal functional RyR2. Phenytoin has an acceptable safety profile as an AAD and has some utility in treating digitalis-induced arrhythmias and suppressing PVCs, however, further study is needed to determine its efficacy as an antiarrhythmic in heart failure patients given new evidence of its RyR2 stabilising properties.