Another trial evaluated the efficacy of candesartan cilexetil, another angiotensin-receptor antagonist, and enalapril maleate in 227 patients (2). These two agents were equally efficacious. Mean reductions in systolic and diastolic blood pressure were 10.5 and 10.1 mm Hg with candesartan and 15.0 and 12.3 mm Hg with enalapril; but, adverse reactions were more frequent in the enalapril group (23.5%) than in the candesartan group (11.3%). In addition, in randomized, multicenter, double-blind trials, valsartan reduced long-standing hypertension more than atenolol (4). Thus, angiotensin-receptor antagonists are considered as a first-line therapy over the other antihypertensive agents. But, which of the two angiotensin-receptor antagonists (losartan or valsartan) is more efficacious in treating African-American patients with mild to moderate hypertension?.
According to Dina and Jafari (2), Losartan potassium was the first orally bioavailable, long-acting, nonpeptide angiotensin-receptor antagonist to be used in humans. Based on its pharmacokinetic profile, its peak plasma concentrations are achieved within one hour of oral administration of 50mg capsule, and its bioavailability is 14%. Losartan has a half-life of 1.5-2.5 hours. It undergoes first-pass hepatic metabolism to its active carboxylic acid metabolite, which reaches a much more potent peak plasma concentration in two to four hours and has a half-life of six to nine hours. The most frequent adverse reaction of losartan is dizziness and cough. According to Wellington and Goa (5), valsartan is rapidly absorbed, with a peak plasma concentration reached two hours after oral administration of 80mg capsule, and its absolute bioavailability is 23%. Its half-life is 6-9 hours. Less than 10% of an orally administered dose of valsartan undergoes biotransformation in the liver, and no active metabolites have been identified. In addition, valsartan is extensively bound to plasma proteins.
