ACTIONS AND PHARMACOLOGY This is a highly selective angiotensin II receptor antagonist that blocks the vasoconstrictor and aldosterone-secreting effects of angiotensin II. It selectively blocks the binding of angiotensin II to specific receptors found in vascular smooth muscle and the adrenal gland. 18 It undergoes substantial first-pass metabolism by cytochrome P-450 enzymes and is converted to an active metabolite. The half-life of losartan is about 2 h and of the metabolite is about 6 to 9 h. Peak concentrations of losartan and its active metabolite are reached in 1 h and in 3 to 4 h, respectively.
INDICATIONS Losartan has been used in clinical trials in the treatment of hypertensive urgency.
USE It is available as 10-, 25-, or 50-mg tablets. The 50-mg dose has been found in studies to produce better results than the lower doses, but higher doses do not produce a more significant blood pressure reduction.
SIDE EFFECTS AND CONTRAINDICATIONS Because of potential fetal injury, the use of losartan should be avoided in the second and third trimesters of pregnancy. Dosing should be decreased in patients with hepatic insufficiency.
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