Angiotensin converting enzyme inhibitors in the clinic: first-dose hypotension.

A fall in blood pressure occurs, in most patients, within a few hours of a single dose of an angiotensin converting enzyme (ACE) inhibitor. While a serious fall in pressure is unusual in previously untreated essential hypertension, some patients are at risk of severe first-dose hypotension. These include those with treated heart failure, severe hypertension on polypharmacy, 'renin-dependent' renovascular hypertension and the occasional elderly patient. In such groups of patients the incidence of severe, symptomatic first-dose hypotension approaches 10%. This effect is not specific for ACE inhibitor therapy and may well occur as frequently with other drugs in such patients. First-dose hypotension may not be accompanied by tachycardia, possibly as a result of a parasympathomimetic action that may contribute to the first-dose effect. It is generally not possible to predict patients at risk, although plasma renin and angiotensin II concentrations show a modest positive correlation with the initial fall in blood pressure. The maximum initial hypotensive effect of ACE inhibitors is not clearly dose related but the duration of effect may be. Therefore such drugs should be started at minimum effective dosage. High-risk patients should be observed closely for at least 6 h. Symptomatic hypotension usually responds to supine rest although infusion of angiotensin II, atropine and occasionally saline may be required.