CONCOMITANT USE OF HCTZ ALONE OR IN COMBINATION WITH TRIAMTERENE IS CONTRAINDICATED. INHIBITORS OF RENAL CATIONIC SECRETION E.G., TRIAMTERENE, METFORMIN AND AMILORIDE ARE CONTRAINDICATED WITH TIKOSYN AS THEY MIGHT INCREASE DOFETILIDE LEVELS. INHIBITORS OF ISOENZYME CYP 3A4 (E.G., MACROLIDE ANTIBIOTICS, AZOLE ANTIFUNGAL AGENTS, PROTEASE INHIBITORS, SEROTONIN REUPTAKE INHIBITORS, AMIODARONE, CANNABINOIDS, DILTIAZEM, GRAPEFRUIT JUICE, NEFAZADONE, NORFLOXACIN, QUININE, ZAFIRLUKAST) SHOULD BE CAUTIOUSLY COADMINISTERED WITH TIKOSYN AS THEY CAN POTENTIALLY INCREASE DOFETILIDE LEVELS. USE OF TIKOSYN IN CONJUNCTION WITH OTHER DRUGS THAT PROLONG THE QT INTERVAL IS NOT RECOMMENDED. SUCH DRUGS INCLUDE PHENOTHIAZINES, CISAPRIDE, BEPRIDIL, TRICYCLIC ANTIDEPRESSANTS, CERTAIN ORAL MACROLIDES, AND CERTAIN FLUOROQUINOLONES. CLASS I OR CLASS III ANTIARRHYTHMIC AGENTS SHOULD BE WITHHELD FOR AT LEAST THREE HALF-LIVES PRIOR TO DOSING WITH TIKOSYN.