& decreased clearance w/ cimetidine, propranolol, allopurinol, macrolide antibiotics (erythromycin), OCs, alkalinizing agents, influenza vaccine. Decreased t½
& increased clearance w/ phenytoin, barbiturates, carbamazepine, isoproterenol, rifampin, smoking (tobacco), acidifying agents. Increased cardiac effect of digitalis glycosides; diuresis of thiazides; nephrotoxicity of nephrotoxic drugs. Increased ratio of lithium/CrCl, thus decreased serum lithium. Increased toxicity & CNS stimulation of sympathomimetic amines. Decreased anticoagulant activity, increased prothrombin & fibrinogen blood conc, shorten prothrombin time of coumarin anticoagulants. Decreased antihyperuricemic action of allopurinol; uricosuric action of probenecid & pyrazolon derivatives; threshold value for inducing convulsions of ketamine.