Increased incidence of hypotension, hyperkalemia & changes in renal function w/ other drugs blocking RAS eg, ACE inhibitors or aliskiren. Increased serum K levels w/ K-sparing diuretics or K supplements. Decreased antihypertensive effects w/ NSAIDs including COX-2 inhibitors. Increased systemic exposure to valsartan w/ inhibitor of the uptake transporter (rifampin, ciclosporin) or efflux transporter (ritonavir). Increased lithium conc & toxicity.