Losartan potassium is an angiotensin II receptor (type AT1) antagonist. Losartan potassium, a non-peptide molecule, is chemically described as 2-butyl-4-chloro-1-[p-(o-1H-tetrazol-5- ylphenyl)benzyl]imidazole-5-methanol monopotassium salt.

Losartan potassium is a white to off-white free-flowing crystalline powder with a molecular weight of 461.01. It is freely soluble in water, soluble in alcohols, and slightly soluble in common organic solvents, such as acetonitrile and methyl ethyl ketone. Oxidation of the 5-hydroxymethyl group on the imidazole ring results in the active metabolite of losartan.

Losartan potassium tablets USP are available for oral administration containing either 25 mg, 50 mg or 100 mg of losartan potassium and the following inactive ingredients: lactose monohydrate, microcrystalline cellulose, pregelatinized starch, magnesium stearate, hydroxypropyl cellulose, hypromellose, titanium dioxide, D&C yellow No. 10 aluminum lake and FD&C blue No.2 aluminum lake.