Losartan: Increased incidence of hypotension, hyperkalemia & changes in renal function w/ other agents acting on the renin-angiotensin-system. Reduced active metabolite levels w/ rifampicin & fluconazole. Increased serum K w/ K-sparing diuretics (eg, spironolactone, triamterene, amiloride), K supplements, or salt substitutes containing K. Reduced lithium excretion. Attenuation of antihypertensive effect & may lead to increased risk of worsening of renal function, including possible acute renal failure, & increase in serum K, especially in patients w/ poor pre-existing renal function w/ NSAIDs (ie, selective COX-2 inhibitors, ASA at anti-inflammatory doses) & non-selective NSAIDs. May increase the risk of hypotension w/ TCAs, antipsychotics, baclofen, amifostine. Hydrochlorothiazide: Potentiation of orthostatic hypotension w/ alcohol, barbiturates, narcotics or antidepressants. Dose adjustment of antidiabetics (oral agents & insulin); uricosuric medicinal products (probenecid, sulfinpyrazone). Risk of lactic acidosis w/ metformin. Additive effect w/ other antihypertensives. Impaired absorption w/ cholestyramine & colestipol resins. Intensified electrolyte depletion/imbalance, particularly hypokalemia w/ corticosteroids, ACTH; amphotericin B (parenteral), stimulant laxatives or glycyrrhizin (found in liquorice). Possible decreased response to pressor amines (eg, adrenaline). Possible increased responsiveness to skeletal muscle relaxants, nondepolarizing (eg, tubocurarine). Reduced renal clearance of lithium & high risk of lithium toxicity. May increase incidence of hypersensitivity reactions to allopurinol. Increased bioavailability by decreasing GI motility & stomach emptying rate w/ anticholinergic agents (eg, atropine, biperiden). May reduce renal excretion of cytotoxic agents (eg, cyclophosphamide, methotrexate) & potentiate their myelosuppressive effects. May enhance toxic effect of salicylates (in high dosages) on the CNS. Isolated reports of hemolytic anemia w/ methyldopa. May increase risk of hyperuricemia & gout-type complications w/ cyclosporine. Thiazide-induced hypokalemia or hypomagnesemia may favor onset of digitalis-induced cardiac arrhythmias w/ digitalis glycosides. May increase serum Ca levels due to decreased excretion. Risk of symptomatic hyponatremia w/ carbamazepine. Increased risk of acute renal failure w/ high doses of iodine contrast media.