High blood pressure is a major health problem. Hypertension, if not controlled, may develop serious and often fatal complications, such as stroke, myocardial infarction and renal failure. It affects over 50 million Americans, who have a systolic blood pressure of at least 140 mm Hg or a diastolic blood pressure of at least 90 mm Hg (1). The prevalence of hypertension varies among ethnic groups: 32.4% among non-Hispanic African Americans, 23.2% among non -Hispanic Whites, and 22.6% among Mexican Americans (1). In only one out of four patients, hypertension is adequately controlled by lifestyle modifications and drug therapy (2). .
Drug therapy is focused on blocking the renin-angiotensin system (RAS). The RAS is activated by renin catalyzes the conversion of angiotensinogen to angiotensin I, which is then transformed into active angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II is responsible for aldosterone production and release, vasoconstriction, reabsorption of sodium, increased inotropism and chronotropism, stimulation of thirst, vagus suppression and beta-adrenergic-receptor stimulation; thus, it leads to increases in blood volume and blood pressure (2). Hence, blocking the RAS ultimately leads to decreasing blood pressure. The agents that are used in decreasing blood pressure include ACE inhibitors, calcium-channel blockers, alpha- and beta-receptor blockers, and angiotensin-receptor antagonists. .
Several clinical trials have demonstrated that angiotensin-receptor antagonists are as effective as the other anti-hypertensive agents, such as ACE inhibitors, and induce fewer adverse effects, and that they are preferred as a first-line therapy (3-4). For example, in the first large-scale multicenter study of outpatient subjects with hypertension, oral losartan potassium (an angiotensin-receptor antagonist) at 50mg daily dosage and enalapril maleate (an ACE inhibitor) at 20mg daily dosage were both relatively effective in reducing blood pressure; however, losartan potassium induced fewer adverse effects than enalapril maleate.
