ABSORPTION REDUCED BY ANTACIDS, H2 RECEPTOR ANTAGONISTS, ANTICHOLINERGICS. IT ENHANCES THE ACTIVITY OF ORAL ANTICOAGULANTS, SULPHONYLUREAS, PHENYTOIN.RISK OF CARDIAC ARRHYTHMIAS WHEN GIVEN WITH ASTEMIZOLE, CISAPRIDE, TERFENADINE, QUINIDINE, PIMOZIDE. ISONIAZID, RIFAMPICIN, PHENYTOIN MAY REDUCE ITS PLASMA CONCENTRATION. CONCENTRATION OF RIFAMPICIN & ISONIAZID IS ALSO REDUCED. EFFICACY OF ORAL CONTRACEPTIVE IS REDUCED. IT INCREASES PLASMA CONCENTRATION OF ASTEMIZOLE, TERFENADINE, BENZODIAZEPINES, CISAPRIDE, CORTICOSTEROIDS, CYCLOSPORIN, DELAVIRDINE, INDINAVIR, RITONAVIR, ORAL ANTICOAGULANTS, PACLITAXEL, SERTINDOLE, LOVASTATIN, SIMVASTATIN, ZIDOVUDINE, CALCIUM CHANNEL BLOCKERS, PIMOZIDE, QUINIDINE, SILDENAFIL, TACROLIMUS, BUSPIRON, BUSULPHAN, CARBAMAZEPINE, DIGOXIN, DOCETAXEL, RIFABUTIN, TRIMETREXATE & VINCA ALKALOIDS. THEOPHYLLINE CLEARANCE IS REDUCED.