Diuretics

Diuretics (also called water pills or fluid pills) are medicines that increase the amount of urine you produce. Urination is the body’s way of removing excess salt and water.  Not only does this relieve symptoms such as ankle swelling, it also helps to lower blood pressure, and relieve fluid from around your heart.

There are several different classes of diuretics, including carbonic anhydrase inhibitors, loop diuretics, potassium-sparing diuretics, and thiazide diuretics. Each type works in a distinct way and in different parts of the kidney cell (called a nephron).

What are diuretics used for?

Diuretics are used to treat conditions that have fluid retention (also called edema) as a symptom, such as heart failure, kidney failure, and cirrhosis of the liver.

They are also effective at reducing blood pressure and some (such as thiazides and loop diuretics) are used for the treatment of high blood pressure (hypertension). Carbonic anhydrase inhibitors are mainly used for the treatment of glaucoma and are sometimes used off-label for altitude sickness.

What are the differences between diuretics?

Each class of diuretic works in a different way to remove salt and water from the kidney, which means they have different potencies and different side effects. Below, we have grouped the most common diuretics into their respective classes.

Thiazide diuretics

Thiazide diuretics inhibit the sodium/chloride cotransporter located in the distal convoluted tubule of a kidney cell. This decreases the amount of sodium reabsorbed back into the body, which results in more fluid being passed as urine. Thiazides are relatively weak diuretics.

Loop diuretics

Loop diuretics work by inhibiting the sodium-potassium-chloride (Na+/K+/2Cl) cotransporter in the thick ascending loop of Henle, a distinct area in the kidney cell. These are potent diuretics.

Potassium-Sparing Diuretics

Potassium-sparing diuretics interfere with the sodium-potassium exchange in the distal convoluted tubule of a kidney cell. Some block the aldosterone receptor. Aldosterone is a hormone that promotes the retention of sodium and water. They are relatively weak diuretics; however, they do not cause hypokalemia (low potassium levels) but may cause hyperkalemia (high potassium levels), especially if they are used with other agents that also retain potassium, such as ACE inhibitors.

Carbonic anhydrase inhibitors

Carbonic anhydrase inhibitors act by increasing the amount of bicarbonate, sodium, potassium, and water excreted from the kidney. They are relatively weak diuretics. They also reduce fluid levels in the eye and may be used to treat glaucoma and are sometimes used off-label to treat altitude sickness.

Are diuretics safe?

When taken at the recommended dosage, diuretics are considered safe. However, they have been associated with several serious adverse effects including:

• Stevens-Johnson syndrome, erythema multiforme and other severe reactions in people with a sulphonamide allergy who have taken a sulphonamide-containing diuretic (includes acetazolamide, thiazides, or loop diuretics)
• Severe neurological changes have occurred in people with liver disease given loop diuretics who are already electrolyte depleted
• Tinnitus or hearing impairment have been reported with loop diuretics, mainly after intravenous administration, or in people with kidney disease, low protein levels, or administered another medicine that may also affect hearing
• Excessive urination can occur which may cause dehydration with the potential for adverse cardiovascular events such as a stroke or blood clots.

What are the side effects of diuretics?

Side effects vary depending on the type of diuretic taken: however, the more common side effects of diuretics include:

• Changes in electrolyte levels (such as potassium, sodium, calcium or magnesium levels), depending on the type of diuretic
• Constipation
• Dizziness
• Dry mouth
• Gout
• A headache
• An increase in blood sugar levels
• Muscle cramps
• Stomach upset
• Tiredness.

For a complete list of side effects, please refer to the individual drug monographs.