Enhanced effects of L-dopa, dopaminergic agonists & anticholinergics. Reduced effects of barbiturates & neuroleptics. Modified effects of antispasmodic agents, dantrolene or baclofen. Avoid concomitant use w/ NMDA antagonists eg, amantadine, ketamine or dextromethorphan. Possible risk w/ phenytoin. Increased plasma levels w/ cimetidine, ranitidine, procainamide, quinidine, quinine & nicotine. Possible reduction of hydrochlorothiazide serum level. Increased INR w/ warfarin. Consider possible drug interaction w/ benzodiazepines & antidepressants.