Losartan: Decreased conc by rifampin. Increased serum K w/ K-sparing diuretics (eg, spironolactone, triamterene, amiloride), K supplements or K-containing salt substitutes. Reduced lithium excretion. Attenuated antihypertensive effects by NSAIDs including selective COX-2 inhibitors. Closely monitor BP, renal function & electrolytes w/ ACE inhibitors. Hydrochlorothiazide: Potentiated orthostatic hypotension w/ alcohol, barbiturates or narcotics. Adjust dosage w/ oral antidiabetics & 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, norepinephrine. 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.