What you need to know about diuretics


Diuretics, also known as water pills, increase urine flow by helping to remove salt and water from the body. They generally work by flushing salt from the kidneys into a person's urine. This process helps lower blood pressure by reducing the amount of blood the heart has to pump. Diuretics can also be used to treat heart failure, liver failure, and kidney disease.

Below is a comprehensive guide to the different types of diuretics and how they work.

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Diuretics increase the volume of urine produced and alter the composition of electrolytes or salts in the body. It is difficult to understand the various biochemical mechanisms of action of diuretics. For example, urine output includes concentration gradients, osmosis, carriers, etc.

In a general sense, diuretics remove excess fluid (water) from our body. There are many conditions that improve with fluid secretion, including hypertension, heart failure, brain swelling (edema), eye swelling (eye swelling), and swelling secondary to liver or kidney disease.

Before learning how diuretics work, let's take a quick look at the anatomy of the nephron and kidney tubules. Diuretics work on different parts of the nephron, the main component of the kidney that filters urine.

A look at the nephron

Here is a summary of the anatomy of the nephron:

  • Blood flows from the body into the renal corpuscle, which consists of glomeruli, a bundle of capillaries, and Bowman's capsule. The renal corpuscle is the first stage of urine filtration.
  • The glomeruli are connected to the renal tubules, a system of microscopic tubes that produce urine. The first part of the renal tubule is the proximal convoluted tubule.
  • The proximal convoluted tubule flows into the loop of Henle. The first part of the loop is the descending branch, the second is the thick ascending branch.
  • The ascending branch enters the distal convoluted tubule.
  • The distal convoluted tubule attaches to the collecting duct .

Carbonic anhydrase inhibitors

Carbonic anhydrase inhibitors such as acetazolamide work by inhibiting the enzyme carbonic anhydrase located in the proximal convoluted tubule. Carbonic anhydrase is generally responsible for the absorption of sodium ( NHE3 antiporter ), potassium, water, amino acids, and sugars back into the blood. By inhibiting this enzyme, medications such as acetazolamide increase the amount of water in the renal tubular system. Carbonic anhydrase inhibitors are used primarily to treat glaucoma .

Sodium glucose cotransporter 2 (SGLT2) inhibitors

Sodium glucose cotransporter 2 (SGLT2) inhibitors are phosphorylated ribonucleotides that act on the sodium glucose cotransporter located in the proximal convoluted tubule. They suppress the action of this carrier and reduce the reabsorption of glucose and sodium ions in the blood. With less reabsorbed sodium ions, less water follows (osmosis) and, as a result, moderate diuresis is observed. Although SGLT2 drugs such as canagliflozin and dapagliflozin are technically mild diuretics due to their effect on sugar, they are used primarily to treat diabetes .

Loop diuretics

Loop diuretics, such as furosemide, inhibit the Na / K / 2Cl transporter in the thick ascending loop of Henle; therefore, the reabsorption of sodium and water in the blood is reduced. Since loop diuretics also affect potassium reabsorption, a loss of potassium can occur. If the potassium loss is severe enough, it can lead to hypokalemia . In particular, hypokalemia can alter heart function. use) .


Thiazides work by screwing a Na / Cl transporter into the distal convoluted tubules. In addition to blocking the reuptake of sodium and water ions, thiazides also lead to potassium loss. Thiazides are used as first-line therapy for hypertension; In fact, a famous study found that thiazides are more effective as a first-line treatment for hypertension than ACE inhibitors.

When the glomerular filtration rate (a measure of kidney function) is very low, thiazides don't work as well. It should be noted that thiazides are often combined with loop diuretics for a synergistic effect.

In addition to hypertension, thiazides are also used to treat calcium-containing kidney stones and diabetes insipidus (unlike the much more common type 1 and 2 diabetes) .

Potassium-sparing diuretics

As the name suggests, potassium-sparing diuretics increase urine volume without losing potassium. Potassium-sparing agents, such as spironolactone or amiloride, act on the collecting tubules, but use different mechanisms of action.

It is not well known that spironolactone antagonizes aldosterone. Aldosterone is a steroid hormone produced by the adrenal cortex. By counteracting aldosterone, retention of potassium, sodium and water is reduced. Spironolactone is often used to counteract potassium loss caused by thiazide and loop diuretics. This drug is also prescribed after a heart attack or used to treat aldosteronism from any cause.

Amiloride blocks the sodium channels in the collecting ducts and thus blocks the reabsorption of water in your body. Like spironolactone, amiloride is often used to counteract potassium loss caused by other diuretics .

Osmotic diuretics

Osmotic diuretics pass through your body unchanged. When an osmotic diuretic like mannitol enters the kidney tubules, they attract water through osmosis. (Remember that in osmosis, water follows highly concentrated solutes. Additionally, osmotic diuretics in the vasculature outside the kidneys (such as in the brain or eyes) can also drain the water and reduce swelling.

In addition to treating both ocular edema (glaucoma) and cerebral edema (increased intracranial pressure), osmotic diuretics are also used for kidney failure secondary to increased solute load from chemotherapy or rhabdomyolysis (muscle breakdown). In other words, by diluting the drugs and the muscle parts of the nephron, the kidneys are less stressed .


The antagonists of the vasoreceptors or vaptans (conivaptan and tolvaptan) represent a new class of drugs. They work by antagonizing vasopressin or antidiuretic hormone and allowing your body to release electrolyte-free water. Therefore, vaptans are useful in hyponatremic conditions defined by low blood sodium levels, such as SIADH .

Get the word of drug information

If you have high blood pressure or another medical condition that diuretics can help, talk to your doctor. Most diuretics are prescription drugs, and although some are available without a prescription, increased urine volume and changes in electrolyte levels can cause some side effects, including dehydration. Diuretics can also make other conditions worse, so it's best to talk to your healthcare provider about diuretics first.

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