May enhance mode of action of L-dopa, dopaminergic agonists & anticholinergics. May reduce efficacy of barbiturates & neuroleptics. May modify effects of antispasmodic agents eg, dantrolene or baclofen. Increased risk of pharmacotoxic psychosis w/ amantadine, ketamine, dextromethorphan & phenytoin. Potential risk of increased plasma levels w/ cimetidine, ranitidine, procainamide, quinidine, quinine & nicotine. May reduce serum level of hydrochlorothiazide (HCT). Concomitant use w/ warfarin may increase INR.