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Blockade of the renin-angiotensin system by angiotensin converting enzyme (ACE) inhibitors has an established role in the management of hypertension, heart failure, patients post-myocardial infarction and renal impairment. The mechanism of action of angiotensin II antagonists offers the potential of more complete blockade of angiotensin II, selective inhibition of the AT1 receptor and specificity for the renin-angiotensin system. Whether these mechanistic differences enhance the clinical potential of these drugs remains to be established. Preliminary evidence suggests that ACE inhibitors and angiotensin II antagonists have similar antihypertensive, haemodynamic and nephroprotective effects. Several major outcome trials with angiotensin II antagonists are underway and these should determine the eventual clinical potential of this class. Early results suggest equivalence with ACE inhibitors but further direct comparisons are needed. Angiotensin II antagonists have one undisputed advantage - excellent tolerability. Given the continuing under-use of ACE inhibitors because of concerns about adverse effects, this property alone may prove decisive in ensuring that angiotensin II antagonists yield the full clinical potential from blockade of the renin-angiotensin system.