HYPOTENSION POTENTIATED WITH CALCIUM CHANNEL BLOCKERS, ANTIHYPERTENSIVES, PHENOTHIAZINES AND TRICYCLIC ANTIDEPRESSANTS. INCREASE BIOAVAILABILITY OF DIHYDROERGOTAMINES. ALCOHOL CUASES HYPOTENSION AND COLLAPSE. SEVERE HYPOTENSION AND/OR INCREASED FLUID VOLUME REQUIREMENTS HAVE BEEN REPORTED IN PATIENTS RECEIVING CALCIUM CHANNEL BLOCKERS TOGETHER WITH A BETA BLOCKING AGENT WHO UNDERWENT CORONARY ARTERY BYPASS SURGERY USING HIGH DOSE FENTANYL ANESTHESIA. IT MAY ELEVATE SERUM CONC. OF DIGOXIN SO CARE SHOULD BE TAKEN FOR DIGOXIN TOXICITY. MAY EFFECT GLUCOSE LEVELS IN DIABETICS. PLASMA CONCENTRATION OF THEOPHYLLINE. RANITIDINE AND CIMETIDINE INCREASES BIOAVAILABILITY OF CALCIUM CHANNEL BLOCKERS AND ITS EFFECT. CALCIUM CHANNEL BLOCKERS AND BETA BLOCKING AGENTS IS USUALLY WELL TOLERATED, BUT BEEN OCCASIONAL LITERATURE REPORTS SUGGEST THAT THE COMBINATION MAY INCREASE THE LIKELIHOOD OF CONGESTIVE HEART FAILURE, SEVERE HYPOTENSION OR EXACERBATION OF ANGINA. CO-ADMINISTRATION WITH GRAPEFRUIT JUICE RESULTS IN UP TO A 2-FOLD INCREASE IN AUC AND C MAX , DUE TO INHIBITION OF CYP3A4 RELATED FIRST-PASS METABOLISM. EFFECTS OF CALCIUM CHANNEL BLOCKERS IS REDUCED BY PHENYTOIN, CARBAMAZEPINE & PHENOBARBITONES. ITRACONAZOLE, FLUCONAZOLE, CYCLOSPORIN REDUCE ITS METABOLISM. CONCURRENT USE WITH MAGNESIUM SALTS MAY CAUSE PROFOUND HYPOTENSION OR NEUROMUSCULAR BLOCK.