Grug Therapy: Diuretics
Diuretics lower blood pressure in hypervolemic patients by reducing blood volume. They may also work in patients with normal blood volume by increasing venous capacitance. Advantages include low cost and the convenience of once-a-day dosing.
A variety of thiazide-type diuretics are commercially available, including hydrochlorothiazide, chlorthalidone, metolazone, and indapamide. All have similar hypotensive effects, although metolazone could be more effective in the presence of impaired renal function. All are capable of reversing fluid retention caused by other drugs. Their effectiveness can be reduced by concomitant administration of non-steroidal anti-inflammatory drugs (NSAIDs).
Side effects are dose related. Daily doses larger than 50 mg of hydrochlorthiazide rarely have significant additional hypotensive effect and only worsen potential adverse metabolic effects, including hypokalemia, hypomagnesemia, hyperuricemia, hyperglycemia, hypercholesterolemia, hyponatremia, and metabolic alkalosis. Other possible adverse effects of these drugs include impotence, urinary frequency, and (rarely) pancreatitis.
The need for potassium-sparing diuretics can be minimized by using low doses of thiazide agents. For patients who develop significant hypokalemia (<3.0 mmol/L) or who are receiving digoxin therapy, potassium-sparing diuretics may be used. In general, their hypotensive effect when used alone is weak (amiloride, spironolactone) or non-existent (triamterene). Such agents are most often used in a combination tablet with a thiazide diuretic. These tablets avoid or reduce the need for potassium supplementation. The cost to the patient is, however, increased, and the dosage of the individual components cannot be adjusted. Moreover, these agents can cause life-threatening hyperkalemia in 1) patients with renal impairment, 2) diabetics with hyporeninemic hypoaldosteronism, and 3) patients receiving other drugs impairing potassium elimination (such as angiotensin-converting enzyme inhibitors).
Loop diuretics (furosemide, ethacrynic acid) are generally reserved for treatment of hypertension in patients with impaired renal function (in whom thiazides may be relatively ineffective) or in patients with fluid retention unresponsive to thiazides.
This post has been viewed 3212 times.
Comments are closed.
