The elderly patient. A special case for diuretic therapy.

Diuretics are among the most widely prescribed drugs, especially for the elderly with cardiac failure or hypertension. Progressive structural and functional changes occur in the kidneys after the fourth decade, leading to impairment of the ability of the kidneys to handle sodium, water and solutes. The renal reserves of the elderly are about half those of the young. In addition, the renin-aldosterone system shows reduced activity in old age. The pharmacokinetics and pharmacodynamics of diuretics in the elderly are reviewed, and the influence of congestive cardiac failure is emphasised with regard to the kinetics of diuretics and the deleterious effect of diuretic-induced hypokalaemia and hypomagnesaemia on the pharmacology of digoxin. Guidelines are suggested for the use of diuretics in the elderly, including the avoidance of unnecessary use, the careful choice of diuretic used, the need for small initial doses, and the prevention of hypokalaemia. The place of potassium-sparing agents for the elderly and adverse effects of diuretics, either mechanical, metabolic or toxic are discussed. Mechanical problems are related to the rate and volume of urine produced, and the resulting effects on bladder function and on blood volume. Although toxic effects are relatively rare, metabolic effects include electrolyte changes, impairment of glucose tolerance, and increased serum uric acid and lipids. Most of these adverse effects are preventable by careful management; the consensus is that they are not of sufficient clinical significance to outweigh the long record of efficacy and safety of diuretic therapy in the elderly. Diuretics will, and should, continue to be used extensively in elderly patients with hypertension and/or cardiac failure.