In vitro and in vivo pharmacology of olmesartan medoxomil, an angiotensin II type AT1 receptor antagonist

Abstract

Olmesartan medoxomil is a new non-peptide angiotensin (A) II antagonist under development for treating hypertension. It is a pro-drug containing an ester moiety that, after oral administration, is rapidly cleaved to release the active form olmesartan (RNH-6270). In vitro, olmesartan is a highly potent, competitive and selective All AT1 receptor antagonist with almost no antagonistic activity on AT2 and AT4 receptors. Olmesartan produces selective insurmountable inhibition of All-induced contractions of the guinea-pig aorta and is much more potent than losartan in reducing maximal responses. In vivo, intravenous olmesartan produces a rapid and long-lasting inhibition of All-induced pressor responses in conscious rats. Oral olmesartan medoxomil also inhibits All-pressor response but onset of the action is slower compared with intravenous administration. Following oral administration, olmesartan has a faster onset but similar potency when compared with candesartan cilexetil, and clearly exceeds losartan in both respects. Oral olmesartan medoxomil exhibits dose-dependent antihypertensive effects in several rat and dog models, with the most marked effects seen in high plasma renin models, when compared with normal or low renin types. Haemodynamic studies in spontaneously hypertensive rats and normotensive dogs showed intravenous olmesartan selectively reduces renal vascular resistance, which suggests that vasodilatation in the renal vascular bed contributes most to the antihypertensive action of the drug. Long-term treatment with olmesartan medoxomil exhibits, beside antihypertensive effects, beneficial effects in animal models of various types of nephrosis and heart failure, and anti-atherogenic effects in hyperlipidaemic animals. Olmesartan medoxomil is worthy of clinical development in essential and renal hypertension, particularly where renal function is threatened by underlying diabetic disease.