Losartan: Potentiated antihypertensive effects by drugs or other BP-lowering agents. Additive hyperkalaemic effect w/ K supplements, K-sparing diuretics or other drugs causing hyperkalaemia. Increased risk of renal impairment (particularly in those who are inadequately hydrated) & attenuated hypotensive effect w/ NSAIDs. Interactions w/ drugs affecting CYP450 isoenzymes. Hydrochlorothiazide: Potentiation of orthostatic hypotension w/ alcohol, barbiturates, narcotics or antidepressants. Antidiabetics eg, oral agents & insulin (may influence glucose tolerance). Risk of lactic acidosis w/ metformin.