Losartan belongs to a group called angiotensin II receptor blockers (ARB). Losartan was initially marketed as Cozaar, but has recently become the first generic ARB medication available in the United States. Losartan acts as a competitive inhibitor at the receptors of the angiotensin 2 receptor sites primarily on the tiny arteries called arterioles. Activation of the angiotensin receptor leads to vasoconstriction of the arterioles and raises blood pressure. The ARB medictions are closely related to the angiotensin converting enzyme (ACE) inhibitors which work a step earlier in the angiotensin activation system, but often avoid the pulmonary cough side effect so common with the ACE inhibitors.

Losartan dosage is available as 25 mg, 50 mg and 100 mg capsules, and a typical dose is 50-100 mg daily, although some patients have better efficacy when losartan dosage is given twice daily as the losartan half-life is relatively short for a once daily The hypotensive effect of losartan is significantly enhanced when used in combination with a thiazide diuretic, and losartan is available in combination losartan-HCTZ fixed dose tablets or capsules at 50-12.5, 100-12.5 and 100-25 mg combination. THe starting losartan dosage for children below 50kg is 25mg daily for treatment of heart failure and high blood pressure. Losartan is often used when patients are unable to tolerate angiotensin converting enzyme inhibitor (ACEi) due to side effects. Using losartan in combination with an ACE inhibitor is done occasionally, but the additive side effects of raising serum potassium can sometimes make this combination intolerable.

Losartan side effects include first dose hypotension, dizziness and headache; after taking Losartan for a period of time there can be an accumulation of potassium salts in the body, therefore usually periodic checks of the serum potassium level is recommended.

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