Increased AV conduction time w/ β-adrenoceptor blockers. Increased sensitivity w/ agents causing hypokalaemia or intracellular K deficiency eg, lithium salts, corticosteroids, carbenoxolone, some diuretics. Moderate increased risk of toxicity in heart failure patients w/ sennosides. Increased susceptibility to effects of suxamethonium-exacerbated hyperkalaemia. Serious arrhythmias in digitalized patients w/ IV Ca. Increased serum levels w/ amiodarone, flecainide, prazosin, propafenone, quinidine, spironolactone, macrolides (eg, erythromycin, clarithromycin), tetracyclines, gentamicin, itraconazole, quinine, trimethoprim, alprazolam, indomethacin, propantheline, nefazodone, atorvastatin, cyclosporine, epoprostenol (transient), tolvaptan, carvedilol, verapamil, felodipine, tiapamil. Reduced serum levels w/ antacids, some bulk laxatives, kaolin-pectin, acarbose, neomycin, penicillamine, rifampicin, some cytostatics, metoclopramide, sulfasalazine, adrenaline, salbutamol, cholestyramine, phenytoin, St. John's wort. Increased blood conc, enhanced absorption & reduced renal clearance w/ P-glycoprotein inhibitors.