Loop diuretics such as furosemide are potent reducers of blood pressure. Here is how they work, what side effects they cause, and what they are good for.
Potent diuretics with significant blood pressure-lowering properties are the loop diuretics. These are called thus because of their locus of operation at the loop of Henle where they inhibit a sodium-potassium pump. This results in a powerful diuresis. Volume reduction, as a result, reduces blood pressure. The most famous and most widely used of these is furosemide. Anecdotal transient vasodilation may also contribute to blood pressure reduction but is probably negligible. Despite their potency, loop diuretics are not considered proper antihypertensive medications and are not indicated in the treatment of hypertension. This doesn’t mean, though that they aren’t sometimes used precisely for that and are quite effective when combined with beta-blockers which block the compensatory tachycardia which would otherwise develop in response to volume reduction.
Limitations of loop diuretics
Loop diuretics suffer from several limitations. To function they need to reach the loop of Henle. This means that in renal failure, higher doses are required to achieve an effect. Also, only furosemide bound to albumin can reach the kidney. This means that in situations of severe hypoalbuminemia these medications will have little or no effect. When used for fluid reduction in nephrotic syndrome, it is sometimes necessary to administer intravenous albumin along with the furosemide just to get it to function. Loop diuretics cause potassium depletion as well as calcium depletion. These diuretics are often prescribed in combination with potassium supplementation to prevent hypokalemia. As diuretics, significant volume depletion can occur. This can result in elevated creatinine and uric acid as well as orthostatic hypotension, as seen in dehydration. The half-life of furosemide is short – six hours or less. After this time, the kidney will compensate by retaining fluids. Thus for effective blood pressure reduction, it makes sense to administer the medication twice daily at least.
The primary use
The primary use of these diuretics is in problems of volume overload as in congestive heart failure where diuretics can help the body excrete excess fluids.
Another use of loop diuretics is to help in urinary excretion of excessive blood levels of calcium as in primary hyperparathyroidism.