[For which hypertensive patient should angiotensin-converting enzyme inhibitor be prescribed or forbidden?]

Angiotensin-converting enzyme (ACE) inhibitors act by lowering the level of angiotensin II. The therapeutic benefits of these drugs and their potential side-effects therefore result from suppression of the physiological effects of angiotensin II. It is rational to prescribe an ACE inhibitor when the renin-angiotensin system is activated, as in renin-dependent essential hypertension, malignant hypertension and hypertension associated with heart failure. The beneficial effects of ACE inhibitor must be weighed against the special risks of renovascular hypertension: risk of renal artery thrombosis in case of unilateral stenosis and risk of renal failure if the stenosis is bilateral or affects a solitary kidney. In some situations the renin-angiotensin system is not directly involved in hypertension but may play a local haemodynamic role, as in some cases of primary or diabetic nephropathy. In such case the ACE inhibitors are thought to exert a protective effect. ACE inhibitors were reputed to be less effective in the elderly than in younger patients, but we now know that they can be prescribed with equal success in both instances to reduce peripheral resistance and improve regional blood flow as well as arterial compliance. Finally, ACE inhibitors can be prescribed, albeit with limited effectiveness, when the renin-angiotensin system is not activated, as in low renin hypertension and idiopathic hyperaldosteronism due to adrenal hyperplasia. They are ineffective in case of Conn's adenoma and contra-indicated in pregnant women.