Increased risk of ventricular arrhythmias, notably torsades de pointes w/ antiarrhythmic drugs class IA (eg, quinidine, hydroquinidine, disopyramide), III (eg, amiodarone, sotalol, dofetilide, ibutilide); non-antiarrhythmic drugs eg, astemizole, bepridil, cisapride, diphemanil, IV erythromycin, halofantrine, lumefantrine, methadone, moxifoxacin, pentamidine, sotalol, IV spiramycin, sparfloxacin, terfenadine, vincamine, some antipsychotics like pimozide, haloperidol, benzamides. Risk of hypokalemia & -ve AV conduction effect w/ digitalis glycosides. Increased risk of hypotension w/ other antihypertensive agents, tricyclics, phenothiazines, baclofen, amifostine. Reduced antihypertensive efficiency w/ NSAIDs; corticosteroids, tetracosactide. Bisoprolol: Increased risk of ventricular arrhythmias or torsades de pointes w/ sultopride. Risk of bradycardia, negative influence on contractility & AV conduction w/ verapamil, diltiazem, bepridil; propafenone, cibenzoline, flecainide. Decreased central sympathetic tonus w/ centrally-acting antihypertensive drugs eg, clonidine, methyldopa, moxonidine, rilmenidine. Increased lidocaine plasma levels. Mask warning signs of hypoglycemia w/ antidiabetics eg, insulin, sulphonylureas, glinides. Increased risk of bradycardia w/ other bradycardia-inducing drugs eg, anticholinesterases, digitalis glycosides, mefloquine. Increased risk of hypotension w/ dihydropyridine type Ca channel blockers eg. nifedipine, amlodipine. Additive systemic effect w/ topical β-blockers. Hydrochlorothiazide: Increased lithium plasma levels. Reduced glomerular blood flow w/ systemic NSAIDs, ASA. Hypo- or hyperkalemia w/ K-sparing diuretics. Increased risk of hypokalaemia w/ hypokalemic drugs eg, IV amphotericin, systemic corticosteroids, tetracosactide, stimulating laxatives. Decreased BP &/or acute renal failure w/ ACE inhibitors, AIIA. Symptomatic hyponatremia w/ carbamazepine. Increased risk of acute renal failure w/ iodinated contrast media. Reduced absorption by resins. Attenuated effect w/ uric acid-lowering agents. Hypercalcemia w/ Ca salts. Increased risk of creatininemia w/ cyclosporine.