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Losartan: profile and news
Merck profits edge ahead in fourth quarter Feb 1, 2006 Other information Indication For the treatment of hypertension Pharmacology Losartan is the first of a class of antihypertensive agents called angiotensin II (AG II) receptor antagonists. It is, along with its longer acting active metabolite (E-3174), a specific and selective AT1 receptor antagonist. Losartan blocks the vasoconstrictor and aldosterone-secreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor found in many tissues, (e.g., vascular smooth muscle, adrenal gland). Mechanism Of Action Losartan and its longer acting active metabolite (E-3174) interfere with the binding of angiotensin II to the angiotensin II AT1-receptor by, themselves, binding reversibly to the receptors in vascular smooth muscle and the adrenal gland. As angiotensin II is a vasoconstrictor, which also stimulates the synthesis and release of aldosterone, blockage of its effects results in decreases in systemic vascular resistance. Neither Losartan or its metabolite inhibit the angiotensin converting enzyme, other hormone receptors, or ion channels. Drug Category Antihypertensive Agents; Antiarrhythmic Agents; Angiotensin II Receptor Antagonists; ATC:C09CA01 Brand Names/Synonyms CHEMBANK1667; Cozaar; DUP 89; Hyzaar; Lacidipine; Lortaan; Losartan Dosage Forms Tablets Absorption Well absorbed, the systemic bioavailability of losartan is approximately 33% Interactions -->Interactions for Losartan: No significant drug-drug pharmacokinetic interactions have been found in interaction studies with hydrochlorothiazide, digoxin, warfarin, cimetidine and phenobarbital. Rifampin, an inducer of drug metabolism, decreased the concentrations of losartan and its active metabolite. In humans, two inhibitors of P450 3A4 have been studied. Ketoconazole did not affect the conversion of losartan to the active metabolite after intravenous administration of losartan, and erythromycin had no clinically significant effect after oral administration. Fluconazole, an inhibitor of P450 2C9, decreased active metabolite concentration and increased losartan concentration. The pharmacodynamic consequences of concomitant use of losartan and inhibitors of P450 2C9 have not been examined. Subjects who do not metabolize losartan to active metabolite have been shown to have a specific, rare defect in cytochrome P450 2C9. These data suggest that the conversion of losartan to its active metabolite is mediated primarily by P450 2C9 and not P450 3A4. As with other drugs that block angiotensin II or its effects, concomitant use of potassium-sparing diuretics (e.g., spironolactone, triamterene, amiloride), potassium supplements, or salt substitutes containing potassium may lead to increases in serum potassium. As with other antihypertensive agents, the antihypertensive effect of losartan may be blunted by the non-steroidal anti-inflammatory drug indomethacin. |
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