Increased antihypertensive effect w/ other antihypertensive drugs. Concomitant use w/ K supplements, K-sparing diuretics, salt substitutes containing K, or other drugs that may alter K levels (heparin). Reversible increases in serum lithium conc & toxicity. Potentiated action of curare derivatives. Weaken diuretic & antihypertensive activity of thiazide w/ NSAIDs. Increased hypokalemic effect w/ kaliuretic diuretics, corticosteroids, ACTH, amphotericin, carbenoxolone, penicillin G, salicylic acid derivatives. Increase hypersensitivity reactions to allopurinol; adverse effects by amantadine; enhanced hyperglycemic effect of diazoxide; reduced renal excretion of cytotoxic drugs (eg, cyclophosphamide, methotrexate). Increased bioavailability w/ anticholinergic agents (eg, atropine, biperiden). Hemolytic anemia may occur w/ methyldopa. Decreased absorption w/ cholestyramine. Potentiate rise in serum Ca w/ vit D or Ca salts. Increased risk of hyperuricemia & gout-type complications w/ cyclosporine. Hyponatremia may develop w/ carbamazepine.