CONCURRENT USED WITH OTHER ANTIMUSCARINIC DRUGS PRODUCES ENHANCED ANTIMUSCARINIC EFFECTS. CYTOCHROME P-450 ENZYME ACTIVATORS LIKE PHENYTOIN, RIFAMPICIN AND PHENOBARBITONE MAY INCREASE THE CLEARANCE OF IT. BETA BLOCKERS MAY PRODUCE BRADYCARDIA, AND HYPOTENSION. PATIENTS TAKING DISOPYRAMIDE PHOSPHATE AND ERYTHROMYCIN LIKE POTENT CYTOCHROME-P-450 - 3A4 INHIBITORS & DRUGS LIKE KETOCONAZOLE, ITRACONAZOLE, FLUCONAZOLE, MICONAZOLE, NEFAZODONE, FLUVOXAMINE, CIMETIDINE, DILTIAZEM, ISONIAZID, CLARITHROMYCIN, VERAPAMIL, FLUOXETINE, SERTRALINE, TROLEANDOMYCIN, MIBEFRADIL DIHYDROCHLORIDE & QUININE CONCOMITANTLY, MAY DEVELOP INCREASED SERUM CONCENTRATIONS OF DISOPYRAMIDE RESULTING IN EXCESSIVE WIDENING OF THE QRS COMPLEX AND/OR PROLONGATION OF THE Q-T INTERVAL. DISOPYRAMIDE SHOULD NOT BE ADMINISTERED WITHIN 48 HOURS BEFORE OR 24 HOURS AFTER VERAPAMIL ADMINISTRATION.