Losartan: Reduced levels of active metabolite by rifampin & fluconazole. Increased serum K w/ K-sparing diuretics (eg, spironolactone, triamterene, amiloride), K supplements, K-containing salt substitutes or other drugs increasing serum K eg, trimethoprim-containing products. Reduced lithium excretion. Attenuated antihypertensive effects w/ NSAIDS including selective COX-2 inhibitors. Not to be co-administered w/ aliskiren. Hydrochlorothiazide: Potentiated orthostatic hypotension w/ alcohol, barbiturates or narcotics. Adjust dosage w/ oral antidiabetics or insulin. Additive effects w/ other antihypertensive drugs. Impaired absorption w/ cholestyramine & colestipol resins. Intensified electrolyte depletion w/ corticosteroids, ACTH or glycyrrhizin. Decreased response to pressor amines eg, adrenaline. Increased responsiveness to nondepolarizing skeletal muscle relaxants eg, tubocurarine. Reduced renal clearance of lithium. Reduced diuretic, natriuretic & antihypertensive effects w/ NSAIDS including selective COX-2 inhibitors. Lowered active metabolite conc w/ grapefruit juice.