Increased plasma lithium. Concomitant use w/ Torsades de Pointes-inducing drugs eg, class IA (quinidine, hydroquinidine, disopyramide) & class III antiarrhythmics (amiodarone, sotalol, dofetilide, ibutilide, bretylium); antipsychotics (chlorpromazine, cyamemazine, levomepromazine, thioridazine, trifluoperazine, amisulpride, sulpiride, sultopride, tiapride, droperidol, haloperidol, pimozide); bepridil, cisapride, diphemanil, IV erythromycin & vincamine, halofantrine, mizolastine, pentamidine, sparfloxacin, moxifloxacin, methadone, astemizole, terfenadine. Possible reduction in antihypertensive effect & risk of acute renal failure in dehydrated patients w/ systemic NSAIDs including COX-2 selective inhibitors & high dose ASA (≥3 g/day). Risk of sudden hypotension &/or acute renal failure w/ ACE inhibitor. Increased risk of hypokalaemia w/ IV amphotericin B, systemic gluco- & mineralocorticoids, tetracosactide, stimulant laxatives. Increased antihypertensive effect w/ baclofen. Hypokalaemia predisposing to toxic effects of digitalis. Increased incidence of hypersensitivity reactions to allopurinol. Hypo-/hyperkalaemia w/ K-sparing diuretics eg, amiloride, spironolactone, triamterene. Increased metformin-induced lactic acidosis. Increased risk of acute renal failure w/ iodinated contrast media. Additive antihypertensive effect & increased risk of orthostatic hypotension w/ TCAs, neuroleptics. Risk of hypercalcaemia w/ Ca salts. Risk of increased plasma creatinine w/ ciclosporin, tacrolimus. Decreased antihypertensive effect w/ corticosteroids, systemic tetracosactide.