CONCOMITANT USE OF DILCARDIA AND BETA-BLOCKERS IS USUALLY WELL TOLERATED. IF COMBINATION THERAPY IS INITIATED OR WITHDRAWN IN CONJUNCTION WITH PROPRANOLOL, AN ADJUSTMENT IN THE PROPRANOLOL DOSE MAY BE WARRANTED. CONCOMITANT USE WITH CIMETIDINE & RANITIDINE HAS SHOWN A SIGNIFICANT INCREASE IN PEAK DILTIAZEM PLASMA LEVELS & AN ADJUSTMENT IN THE DILTIAZEM DOSE MAY BE WARRANTED. THE DEPRESSION OF CARDIAC CONTRACTILITY, CONDUCTIVITY, AND AUTOMATICITY, AS WELL AS THE VASCULAR DILATION ASSOCIATED WITH ANESTHETICS, MAY BE POTENTIATED BY CALCIUM CHANNEL BLOCKERS. WHEN USED CONCOMITANTLY, ANESTHETICS AND CALCIUM BLOCKERS SHOULD BE TITRATED CAREFULLY. A REDUCTION OF CYCLOSPORINE TROUGH DOSE RANGING FROM 15% TO 48% WAS NECESSARY TO MAINTAIN
CONCENTRATIONS SIMILAR TO THOSE SEEN PRIOR TO THE ADDITION OF DILTIAZEM. CONCOMITANT ADMINISTRATION OF DILTIAZEM WITH CARBAMAZEPINE HAS BEEN REPORTED TO RESULT IN ELEVATED SERUM LEVELS OF CARBAMAZEPINE (40% TO 72% INCREASE) RESULTING IN TOXICITY IN SOME CASES. CONCURRENT USED WITH OTHER CARDIAC DEPRESSANTS SUCH AS AMIODARONE, BETA BLOCKERS, DIGOXIN, AND MEFLOQUINE THERE MAY BE RISK OF BRADYCARDIA AND ATRIOVENTRICULAR BLOCK. IT IS EXTENSIVELY METABOLISED IN THE LIVER BY THE CYTOCHROME P450 ENZYME SYSTEM ; INTERACTIONS MAY BE EXPECTEDWITH ENZYME INDUCERS, SUCH AS CARBAMAZEPINE, PHENOBARBITONE, PHENYTOIN, RIFAMPICIN AND ENZYME INHIBITORS SUCH AS CIMETIDINE. MAY EFFECT GLUCOSE LEVELS IN DIABETICS. PLASMA CONCENTRATION OF THEOPHYLLINE.
IN GENERAL EFFECTS OF CALCIUM CHANNEL BLOCKERS IS REDUCED BY PHENYTOIN, CARBAMAZEPINE & PHENOBARBITONES. ITRACONAZOLE, FLUCONAZOLE REDUCE ITS METABOLISM. CONCURRENT USE WITH MAGNESIUM SALTS MAY CAUSE PROFOUND HYPOTENSION OR NEUROMUSCULAR BLOCK. ALPRAZOLAM'S CLEARANCE IS EFFECTED SO ITS DOSE SHOULD BE REDUCED TO 1/3.