Thiazide diuretics are used to relieve the oedema of heart failure as well as to lower blood pressure. They reduce peripheral vascular resistance and for this effect they have a flat dose response curve - i.e. increasing the dose above one or two tablets has little further effect. The potent "loop" diuretics e.g. frusemide are used for quick results in emergencies, e.g. acute pulmonary oedema, and in chronic heart failure resistant to thiazides. They produce much more potassium loss. In hepatic ascites choice of diuretic should be spironolactone first and cautious use of thiazide with potassium later. Loop diuretics can be dangerous as they readily cause hypokalemia and encephalopathy.
