IT SHOULD NEVER BE GIVEN WITH DRUGS THAT INHIBIT ITS HEPATIC METABOLISM AND DRUGS THAT ARE ARRHYTHMOGENIC LIKE IMIDAZOLE & TRIAZOLE ANTIFUNGALS LIKE KETOCONAZOLE, ITRACONAZOLE, MACROLIDE ANTIBIOTICS LIKE CLARITHROMYCIN, ERYTHROMYCIN,TROLEANDOMYCIN & OTHERS, SEROTONIN REUPTAKE INHIBITORS, HIV- PROTEASE INHIBITORS, NON-NUCLESIDE REVERSE TRANSCRIPTASE INHIBITOR ANTIRETROVIRALS, ANTIMALARIALS LIKE QUININE, HALOFANTRINE, TRICYCLIC ANTIDEPRESSANTS, ANTIPSYCHOTICS, CISAPRIDE, SOTALOL ETC. TERFENADINE & ASTEMIZOLE SHOULD NOT BE USED SIMULTANEOUSLY BECAUSE OF INCREASED CHANCES OF CARDIAC ARRHYTHMIAS. METABOLISM OF ASTEMIZOLE IS INHIBITED BY GRAPE FRUIT JUICE LEADING TO TOXICITY. KETOTIFEN POTENTIATES ITS SEDATIVE EFFECT.