Abstract

Thiazide diuretics such as bendrofluazide and chlorothiazide have been used for nearly 20 years in the treatment of hypertension. They have been regarded as rather weak antihypertensive agents which could be used alone only in mild hypertension and otherwise as adjuvants to more potent drugs in more serious cases.¹ There are however some patients with ‘essential’ hypertension who are very sensitive to diuretics and in whom the pressure may be brought down to normal by a thiazide² or spironolactone³ even when it is initially considerably raised. Furthermore a few patients who are responsive to thiazides are strikingly unresponsive to non-diuretic antihypertensive drugs. Patients particularly likely to respond to a thiazide diuretic⁴ or spironolactone³ commonly have low plasma renin activity and this occurs in about 25% of patients with essential hypertension.⁵ Since plasma renin activity is not routinely estimated it is simplest to identify these patients by observing the response to an adequate trial of a thiazide.