Amiloride (Midamor®, Merck, Sharp and Dohme)

Abstract

Amiloride is a potassium-sparing diuretic that is pharmacologically similar to triamterene. It has been widely used abroad for several years, alone and in combination with hydrochlorothiazide. As a potassium-sparing agent, amiloride appears to be approximately as effective as triamterene and spironolactone and to have a longer duration of action than triamterene, allowing once daily dosing. The diuretic effect of amiloride is mild, as are all agents that act at distal tubular sites. Amiloride appears to have an antihypertensive effect approximating that of the thiazides and spironolactone – an advantage over triamterene, which is devoid of antihypertensive effects. Amiloride will probably be most useful as a potassium-sparing agent in combination with the thiazide and loop diuretics. It should be kept in mind, however, that many patients on thiazide diuretics do not need supplemental potassium or potassium-sparing agents if they have no other complicating factors, such as digitalis therapy. When hypokalemia causes symptoms, a potassium-sparing agent may have advantages over oral potassium supplements in patient tolerance and compliance. Because of the possibility of tumorigenicity and estrogenic side effects, spironolactone's popularity has been decreasing in recent years. Amiloride will probably be a strong competitor of triamterene and spironolactone because of its longer duration of action than triamterene and, from early indications (cf. ticrynafen), more benign side effects than spironolactone. The drug should be used with great caution, if at all, in patients with impaired renal function, however. The benefits of amiloride will have to be weighed against the cost of the drug in individual patients.