AMLODIPINE HAS BEEN SAFELY ADMINISTERED WITH THIAZIDE DIURETICS, BETA-BLOCKERS, ANGIOTENSIN-CONVERTING ENZYME INHIBITORS, LONG-LASTING NITRATES, DIGOXIN, WARFARIN, NON-STEROIDAL ANTI-INFLAMMATORY DRUGS, ANTIBIOTICS, AND ORAL HYPOGLYCEMIC DRUGS. AMLODIPINE IS EXTENSIVELY METABOLISED IN THE LIVER BY THE CYTOCHROME P450 ENZYME SYSTEM, BUT NO INTERACTIONS OCCUR WITH OTHER DRUGS SUCH AS QUINIDINE, CARBAMAZEPINE, PHENYTOIN, RIFAMPICIN, AND ENZYME INHIBITORS, SUCH AS CIMETIDINE AND ERYTHROMYCIN.
DRUG INTERACTIONS OF CALCIUM CHANNEL BLOCKERS IN GENERAL : SEVERE HYPOTENSION AND/OR INCREASED FLUID VOLUME REQUIREMENTS HAVE BEEN REPORTED IN PATIENTS RECEIVING NIFEDIPINE 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 NIFEDIPINE AND ITS EFFECT. CALCIUM CHANNEL BLOCKERS AND BETA BLOCKING AGENTS IS USUALLY WELL TOLERATED, BUT OCCASIONAL LITERATURE REPORTS SUGGEST THAT THE COMBINATION MAY INCREASE THE LIKELIHOOD OF CONGESTIVE HEART FAILURE, SEVERE HYPOTENSION OR EXACERBATION OF ANGINA. CO-ADMINISTRATION OF NIFEDIPINE 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. ALPRAZOLAM'S CLEARANCE IS EFFECTED SO ITS DOSE SHOULD BE REDUCED TO 1/3. 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. . CONCURRENT USED WITH OTHER CARDIAC DEPRESSANTS SUCH AS AMIODARONE, BETA BLOCKERS, DIGOXIN, AND MEFLOQUINE THERE MAY BE RISK OF BRADYCARDIA AND ATRIOVENTRICULAR BLOCK.