Diuretics in cardiovascular therapy. Perusing the past, practising in the present, preparing for the future.

Diuretics are the mainstay of drug therapy in the treatment of many cardiovascular disorders. However, perusal of knowledge of their haemodynamic activities in heart failure and hypertension reveals major gaps. In left ventricular failure complicating acute myocardial infarction, intravenous frusemide reduces the elevated left heart filling pressure with little change in systemic blood pressure, heart rate or cardiac output, and restores the ability of the left heart to handle an acute increase in filling volume. But there is little knowledge of the haemodynamic effects of other intravenous diuretics, oral diuretics or diuretics other than those acting on the loop of Henle in this emergency clinical situation. Even less information is available on the haemodynamic effects of diuretics in patients in chronic heart failure. In patients with valvular heart disease, parenteral mercury and oral thiazides reduce right heart and pulmonary vascular pressures with variable (dose-dependent?) changes in cardiac output. Information on the effect of loop diuretics, the comparative effects of intravenous versus oral routes of administration and dose-response correlations are all lacking. In hypertension, the dose-blood pressure lowering response relationship of orally administered diuretics is relatively flat. The majority of information relates to oral thiazides; there is little reliable information on the anti-hypertensive efficacy of the loop diuretics. The acute and chronic effects of the majority of commonly used diuretics on cardiac and peripheral vascular functions is unexplained. More is known of their potentially adverse metabolic effects than of their possible circulatory benefits in hypertensive patients. Many unwanted side-effects of these drugs have been described; their potential importance is related directly to the disease state and doses in which they are used. In acute heart failure, their potential danger is probably minimal. In the treatment of chronic heart failure their most sinister potential is in the excessive secretion of potassium and magnesium. In hypertensive patients their long-term administration in high-doses may lead to undesirable metabolic effects that tend to offset their blood pressure lowering activity. Despite their drawbacks, diuretics continue to provide the natural first-line treatment of choice of these common cardiovascular syndromes. But more information on their mechanisms of vascular activities and the differences in non-diuretic activity between different compounds is urgently required.