Enhanced effects of L-dopa, dopaminergic agonists, anticholinergics. Reduced effects of barbiturates, neuroleptics. Modified effects of antispasmodic agents, dantrolene or baclofen. Increased plasma levels w/ cimetidine, ranitidine, procainamide, quinidine, quinine, nicotine. Reduced serum level of hydrochlorothiazide. Increased INR w/ warfarin. Avoid use w/ NMDA antagonists eg, amantadine, ketamine or dextromethorphan.