E-3174 is an active carboxylic acid metabolite of losartan and is an antagonist of the angiotensin II receptor, type 1 (AT1). Losartan was the first orally active AT1 receptor antagonist available on the market, and it is the antagonist with which the greatest clinical experience has been accumulated. EXP3174 is 10 to 20 times more potent than losartan and has a longer duration of action than losartan. However, the oral bioavailability of EXP 3174 is very low. Thus, the drug on the market is losartan, but most of the losartan’s antihypertensive effect is due to EXP 3174.