THE TOXIC EFFECTS OF AMINOPHYLLINE AND OTHER XANTHINES ARE ADDITIVE. CONCOMITANT USE WITH OTHER XANTHINE MADICATIONS SHOULD THEREFORE BE AVOIDED. AMINOPHYLLINE CLEARANCE MAY BE REDUCED BY INTERACTION WITH OTHER DRUGS INCLUDING ALLOPURINOL, SOME ANTIARRHYTHMICS, CIMEDINE, DISULFIRAM, FLUVOXAMINE, INTERFERON ALFA, MACROLIDE ANTIBIOTICS AND QUINOLONES, ORAL CONTRACEPTIVES, THIABENDAZOLE. PHENYTOIN AND SOME OTHER ANTICONVULSANTS, THE ANTIVIRAL RITONAVIR, RIFAMPICIN, SULPHINPYRAZONE, AND CIGARETTE SMOKING MAY INCREASE AMINOPHYLLINE CLEARANCE. THERE IS A RISK OF SYNERGISTIC TOXICITY IF IT IS GIVEN CONCOMITANTLY WITH HALOTHANE OR KETAMINE, AND IT MAY ANTAGONISE THE EFFETCS OF ADENOSINE AND OF NON-DEPOLARISING MUSCLE RELAXANTS. THE INTERACTION BETWEEN AMINOPHYLLINE AND BETA BLOCKERS IS COMPLEX. BUT CONCOMITANT ADMINISTRATION TENDS TO BE AVOIDED.