Losartan

Losartan (rINN) is an angiotensin II receptor antagonist drug used mainly to treat high blood pressure (hypertension). Losartan was the first angiotensin II receptor antagonist to be marketed. Losartan potassium is marketed by Merck & Co. Inc. under the trade name Cozaar. , losartan is available in generic form.

As with all angiotensin II type 1 receptor (AT1) antagonists, losartan is indicated for the treatment of hypertension. It may also delay progression of diabetic nephropathy, and is also indicated for the reduction of renal disease progression in patients with type 2 diabetes, hypertension and microalbuminuria (>30 mg/24 hours) or proteinuria (>900 mg/24 hours).

Although clinical evidence shows calcium channel blockers and thiazide-type diuretics are preferred first-line treatments for most patients (from both efficacy and cost points of view), an angiotensin II receptor antagonist such as losartan is recommended as first-line treatment in patients under the age of 55 who cannot tolerate an ACE inhibitor. The LIFE study demonstrated losartan was significantly superior to atenolol in the primary prevention of adverse cardiovascular events (myocardial infarction or stroke), with a significant reduction in cardiovascular morbidity and mortality for a comparable reduction in blood pressure. A study hints that losartan has a beneficial effect on mitochondria by reversing age related dysfunction in maintaining normal blood pressure and cellular energy usage.

Combination with diuretic
Losartan is available as hydrochlorothiazide/losartan, a combination drug with a low dose thiazide diuretic to achieve an additive antihypertensive effect.

Pharmacokinetics
Losartan is well absorbed following oral administration and undergoes significant first-pass metabolism to produce 5-carboxylic acid metabolite, designated as EXP3174. This metabolite is a long-acting (6 to 8 hr), noncompetitive antagonist at the AT1 receptor, and contributes to the pharmacological effects of losartan. EXP3174 is 10-40 times more potent in blocking AT1 receptors than losartan. Losartan's bioavailability is about 32%.

Metabolism is primarily by cytochrome P450 isoenzymes CYP2C9 and CYP3A4. Peak plasma concentrations of losartan and E-3174 occur about one hour and three to four hours, respectively, after an oral dose. Both losartan and E-3174 are more than 98% bound to plasma proteins. Losartan is excreted in the urine, and in the feces via bile, as unchanged drug and metabolites. About 4% of an oral dose is excreted unchanged in urine, and about 6% is excreted in urine as the active metabolite. The terminal elimination half lives of losartan and E-3174 are about 1.5 to 2.5 hours and 3 to 9 hours, respectively.

Research
Losartan has been found to downregulate the expression of transforming growth factor beta (TGF-β) types I and II receptors in the kidney of diabetic rats, which may partially account for its nephroprotective effects. Effects on TGF-β expression may also account for its potential efficacy in Marfan syndrome and Duchenne muscular dystrophy (DMD) – losartan has been shown to prevent aortic aneurysm and certain pulmonary complications in a mouse model of the disease.

Losartan is being studied for use in the treatment of the 20% of breast cancer tumors positive for AGTR1. The University of Michigan Comprehensive Cancer Center announced the result of an animal study which found losartan to "block" - reverse neoplastic changes - caused by this gene.

Mechanism of action and pharmacological actions
Losartan is a selective, competitive angiotensin II receptor type 1 (AT1) receptor antagonist, reducing the end organ responses to angiotensin II. Losartan administration results in a decrease in total peripheral resistance (afterload) and cardiac venous return (preload) All of the physiological effects of angiotensin II, including stimulation of release of aldosterone, are antagonized in the presence of losartan. Reduction in blood pressure occurs independently of the status of the renin-angiotensin system. As a result of losartan dosing, plasma renin activity increases due to removal of the angiotensin II feedback.

Other uses
Losartan is a uricosuric. Because losartan can cause hyperkalemia, potassium supplements or salt substitutes containing potassium should not be used without consulting the prescribing physician.

Losartan is being researched as a possible drug for marked slowing of aortic enlargement in Marfan and related syndromes.

Losartan is being researched as a possible protection against loss of damaged or old muscle.

Losartan has recently been found to be a cognitive enhancer. It improved memory in people with normal blood pressure under standard conditions, as well as during memory impaired tasks (co-administration of scopolamine).

Synthesis


Carini, D. J.; Duncia, J. V.; Wong, P. C. B; 1992,.