Concomitant use w/ other drugs affecting the RAAS. Losartan: Reduced levels of active metabolite w/ rifampin, fluconazole. May increase serum K w/ K-sparing diuretics (eg, spironolactone, triamterene, amiloride), K supplements, K-containing salt substitutes or other drugs that may increase serum K (eg, trimethoprim-containing products). May reduce excretion of lithium. Antihypertensive effects may be attenuated by NSAIDs including selective COX-2 inhibitors. Avoid use w/ aliskiren in patients w/ renal impairment (GFR <60 mL/min). Amlodipine: Increased systemic exposure w/ diltiazem. Plasma conc may be increased w/ strong CYP3A4 inhibitors eg, ketoconazole, itraconazole, ritonavir. Monitor for symptoms of hypotension & edema when coadministered w/ CYP3A4 inhibitors. Concomitant use w/ CYP3A4 inducers.