Figure 746

Angiotensin II receptor antagonists. These drugs antagonize angiotensin II-induced biologic actions, including proximal sodium reabsorption, aldosterone release, smooth muscle vasoconstriction, vascular remodeling, and baroreceptor sensitivity. Antihypertensive efficacy appears dependent on an activated renin-angiotensin system; bilateral nephrectomy and volume expansion abolish their activity. Losartan is a nonpeptide, specific angiotensin II receptor antagonist acting on the antagonist ATi subtype receptor. Peak response occurs within 6 hours of dosing. It is readily absorbed; peak plasma concentrations are achieved within i hour. It has a relatively short terminal half-life of 1.5 to 2.5 hours. Oral bioavailability is approximately 33%. Losartan undergoes extensive first-pass hepatic metabolism to the predominant circulatory form of the drug Exp-3174. This metabolite is 15 to 30 times more potent than losartan with a longer half-life (between 4 and 9 hours). The metabolite is cleared equally by the liver and the kidney; there may be enhanced hepatic clearance in renal insufficiency [15]. Dose reduction is not required in patients with renal insufficiency.

Valsartan is a nonpeptide, specific angiotensin II antagonist acting on the AT1 subtype receptor. Peak response occurs within 6 hours of dosing. Peak plasma concentrations are reached 2 to 4 hours after dosing. The average elimination half-life is about 6 hours. Oral bioavailability is approximately 25%. Dose reduction is not required in patients with renal insufficiency [15].

Irebsartan is a nonpeptide, specific angiotensin II antagonist acting on the AT1 subtype receptor. Peak response occurs in 4 to 8 hours. There is no active metabolite. Dose reduction is not required in patients with renal insufficiency [15].

Side effects

Mechanisms

Hyperkalemia

Blockade of angiotensin II

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