Diuretics: what they are, what types and how they work

Diuretics are remedies that can be used alone or associated with other active substances, to treat high blood pressure, swelling caused by heart, kidney or liver diseases, among others.

There are several types of diuretics available, such as thiazide, loop, potassium-sparing, osmotic or carbonic anhydrase inhibitors, with different mechanisms of action and acting in different regions of the kidney, which should be prescribed depending on the problem to be treated.

1. Thiazide diuretics

These diuretics have as their mechanism of action the inhibition of sodium reabsorption in the initial portion of the distal kidney tubule, increasing its excretion, as well as the excretion of chlorides and, to a lesser extent, of potassium and magnesium, which consequently lead to elimination of water. These remedies have a moderate potency.

Generic / commercial names: Some examples of thiazide diuretics are indapamide (Natrilix, Indapen, Flux), hydrochlorothiazide (Diurix, Hidromed) and chlorothalidone (Higroton).

Therapeutic indications: Generally, diuretics of this class are indicated to reduce blood pressure and for the chronic treatment of edema associated with congestive heart failure, liver cirrhosis and kidney disease.

Most common side effects:  Some of the most common side effects that may occur during treatment with these drugs are dizziness, headache, weakness, nausea, vomiting, cramps, diarrhea, constipation, cholecystitis, pancreatitis and blood and skin disorders.

2. Loop diuretics

Loop diuretics act by inhibiting sodium reabsorption in the ascending branch of the Henle loop, leading to a reduction in tubular water reabsorption. In addition, these remedies also have direct effects on blood flow, causing vasodilation and reduced renal vascular resistance. These remedies have a potent diuretic effect, with a quick onset of short duration

Generic / commercial names:  Furosemide (Lasix, Neosemid) is an example of a widely used loop diuretic. Learn how to use and what contraindications for furosemide .

Therapeutic indications:  Loop diuretics are indicated for the control of acute pulmonary edema and other milder edema types, acute renal failure and arterial hypertension. In addition, they can also be used to treat acute hypercalcemia, as they promote urinary calcium excretion.

Most common side effects:  Some of the side effects that may occur during treatment are electrolyte disturbances, dehydration, hypovolemia, increased levels of creatinine and triglycerides in the blood, gout attacks and increased urine volume. 

3. Potassium-sparing diuretics

These drugs inhibit the excretion of potassium at the terminal level of the distal bypassed tubule and in the collecting tube, which may or may not have an aldosterone antagonistic action.

Spironolactone is a specific aldosterone antagonist, acting mainly on the aldosterone-dependent sodium and potassium ion exchange site, located in the distal outlined tubule of the kidney and leading to increased amounts of sodium and water to be excreted, while potassium is retained .

Generic / commercial names: Some examples of potassium-sparing diuretics are amiloride, which is only associated with other active substances, and spironolactone (Aldactone, Diacqua). See other therapeutic indications for spironolactone .

Therapeutic indications:  Potassium-sparing diuretics have a weak diuretic action and, therefore, are rarely used alone in the treatment of edema or hypertension, and are generally associated with other diuretics. Its co-administration increases the diuretic effect and antihypertensive response to thiazide and loop diuretics. 

Most common side effects: Some of the adverse effects that can occur are expansion of extracellular volume, dehydration and hypernatremia.

4. Osmotic diuretics

These drugs increase the osmolarity of the glomerular filtrate, which induces the movement of intracellular water into an extracellular and vascular space, inducing a marked diuresis, consequently decreasing intracranial pressure and edema and high intraocular pressure.

Generic / commercial names:  20% Mannitol. Find out how mannitol is used .

Therapeutic indications: 20% mannitol is indicated for the treatment of cerebral edema, acute glaucoma, acute renal failure and in preparation for ophthalmic surgery.

Most common side effects:  Some of the most common adverse effects that can occur are nausea, vomiting, thirst, headache, dizziness, tremors, fevers, increased heart rate, chest pain, hypernatremia, dehydration, blurred vision, hives or hypertension .

5. Carbonic anhydrase inhibitor diuretics

These remedies inhibit carbonic anhydrase, which is an enzyme that catalyzes a chemical reaction that involves hydrating carbon dioxide and dehydrating carbonic acid. As a result, there is a decrease in carbonic acid, which leads to the alkalinization of urine, promoting diuresis. 

Generic / commercial names:  acetazolamide (Diamox). Learn how to use and what are the contraindications for Diamox .

Therapeutic indications: Carbonic anhydrase inhibitors are indicated for the treatment of glaucoma, urinary alkalinization, metabolic alkalosis and acute mountain disease.

Most common side effects:  Some of the adverse effects that can occur are metabolic acidosis, expansion of extracellular fluid volume, hyponatremia, headache, drowsiness, nausea, vomiting and dehydration

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