Possible Interaction: Phenytoin and Quinidine

“It significantly increases the plasma concentrations of digoxin, warfarin, many Class I antiarrhythmic drugs quinidine , procainamide, aprindine and flecainide) and Phenytoin , in some instances resulting in overt signs of clinical toxicity, including adverse cardiovascular, cardiac and central nervous system effects.”

“Drug-disposition studies of orally administered quinidine in four normal healthy volunteers indicated that phenobarbital and phenytoin reduced the half-life of quinidine by approximately 50 per cent (control, 3.0 to 6.1 hours, and with anticonvulsants, 1.6 to 2.6 hours).”

“The data suggest DPH differs from other antiarrhythmic drugs such as quinidine and procaine amide.”

“ Phenytoin increased the use-dependent blocking effects on $$\dot V_{\max }$$ of quinidine by slowing the time course of the slow component of reactivation of $$\dot V_{\max }$$ induced by quinidine.”

“with quinidine (40 mg/kg), procainamide (40 mg/kg), phenytoin (40 mg/kg), clofilium (5 mg/kg), verapamil (10 mg/kg), or propranolol (10 mg/kg) reduced the incidence of isoproterenol-induced ventricular fibrillation and death; bretylium (10 mg/kg) and nicotinic acid (100 mg/kg) had no effect.”

“The possible contributions of these effects were studied indirectly by coadministering quinidine with several compounds (d-propranolol, l-propranolol, d-practolol, practolol, pronethalol, and phenytoin ) which have varying effects on these parameters.”