Pharmacological properties of angiotensin II receptor antagonists.

The availability of selective, potent, orally active and long acting nonpeptide angiotensin II type 1 (AT1) receptor antagonists has provided the opportunity to obtain the benefits of selectively blocking the renin-angiotensin-aldosterone system at the level of the AT1 receptor that mediates most, if not all, of the important actions of angiotensin II, and avoid the nonspecificity of the angiotensin I converting enzyme inhibitors. Losartan was the first, but by no means remained the only, AT1 receptor antagonist. Numerous other 'sartans' have emerged in the past several years and successfully completed clinical development. With the exception of eprosartan, all others, ie, candesartan, irbesartan, saprisartan, tasosartan, telmisartan, valsartan and zolasartan, are based on medications of losartan's prototypical chemical structure. Among the current AT1 receptor antagonists, the rank order of the relative binding affinities (highest affinity = 1) is: candesartan 1, telmisartan 10, E3174 (the active metabolite of losartan) 10, tasosartan 20, losartan 50, eprosartan 100 and the prodrug candesartan cilexetil 280. The mode of (functional) AT1 receptor antagonism has been characterized as surmountable/noncompetitive (losartan, tasosartan, eprosartan) or insurmountable/noncompetitive (candesartan, saprisartan, zolasartan, irbesartan, valsartan, telmisartan, E3174). It is very likely that slow dissociation kinetics from the AT1 receptor underlie insurmountable antagonism. However, competitive or noncompetitive antagonism does not determine the antihypertensive efficacy, but the slow off-rate may extend the occupancy of the AT1 receptor and thereby lengthen the duration of the antihypertensive effect.