Enhanced effects of levodopa, dopaminergic agonists, & anticholinergics. Reduced effects of barbiturates & neuroleptics. May modify effects of antispasmodic agents, dantrolene or baclofen. Risk of pharmacotoxic psychosis w/ amantadine, ketamine & dextromethorphan, & possible risk w/ phenytoin. Potential risk of increased plasma levels w/ cimetidine, ranitidine, procainamide, quinidine, quinine & nicotine. Possibility of reduced serum level of hydrochlorothiazide.