Diuretics act on the kidneys by reducing blood volume and increasing the rate of urine excretion.
The reduction in blood volume results in lower blood pressure, making diuretics commonly prescribed for the treatment of high blood pressure.
Diuretics work by increasing the excretion of salt and water through urine. When taking diuretics, you may urinate more frequently, especially after consuming liquids.
However, diuretics can have adverse effects, such as potassium loss. Additionally, they may lead to dehydration, particularly in elderly individuals or those with kidney problems, so careful monitoring is essential.
Diuretics can be classified into several types based on their mechanism of action:
Thiazides are the first-line medication for treating high blood pressure in adults. They are typically not used alone (monotherapy) but in combination with other antihypertensive medications, such as an ACE inhibitor (ACE) or an angiotensin II receptor blocker (ARB).
Thiazides act on the distal convoluted tubule of the kidney, increasing sodium and water excretion. This process can lead to potassium loss, which may sometimes be significant.
Long-term use of thiazides is associated with side effects such as increased uric acid levels in the blood (hyperuricemia) and electrolyte imbalances (e.g., disturbances in sodium and potassium levels).
Common thiazide diuretics include hydrochlorothiazide, chlorthalidone, indapamide, chlorothiazide, and metolazone.
They are also used to treat heart failure and to prevent kidney stones.
Thiazides are ineffective in advanced renal failure, defined as a serum creatinine level greater than 2.5 mg/dL or a creatinine clearance less than 30 mL/min/1.73 m². In such cases, loop or high-ceiling diuretics are preferred.
One concern in recent years is that high-dose thiazides have been linked to increased insulin resistance and a higher risk of type 2 diabetes mellitus. As a result, they are often discontinued at high doses. However, at lower doses, these side effects tend to diminish significantly.
Loop diuretics, also known as high-ceiling diuretics, work by blocking the reabsorption of chloride and sodium in the loop of Henle, a key part of the kidney responsible for most water and electrolyte reabsorption. By inhibiting this process, they significantly increase the excretion of salt and water through urine.
These diuretics are not commonly used for the treatment of uncomplicated high blood pressure.
Their primary indication is for conditions associated with edema (excessive fluid retention), such as heart failure, cirrhosis, nephrotic syndrome, or pulmonary edema.
The main loop diuretics include furosemide, torsemide, and bumetanide.
A notable side effect of loop diuretics is significant potassium loss, which can lead to hypokalemia.
In some cases, they are used in combination with chlorthalidone (a thiazide diuretic) to manage very resistant high blood pressure, especially in patients with advanced chronic kidney disease.
Potassium-sparing diuretics promote the excretion of water and salt through urine while conserving potassium levels.
The main drugs in this category include amiloride, spironolactone, and triamterene.
These diuretics are often used in the treatment of high blood pressure, typically in combination with other diuretics to prevent potassium depletion.
Spironolactone has additional uses, such as the treatment of hirsutism and polycystic ovary syndrome (PCOS). However, it can cause side effects, including gynecomastia (enlargement of the breast tissue in men).
Osmotic diuretics work by increasing the osmolarity of the tubular fluid, enhancing renal filtration and consequently increasing urine volume.
These diuretics are not used for the treatment of high blood pressure. Instead, they are primarily indicated for conditions such as increased intracranial pressure or increased intraocular pressure.
The main drug in this category is mannitol.
Carbonic anhydrase inhibitors promote the excretion of water and electrolytes through urine by inhibiting the enzyme carbonic anhydrase.
These drugs are not used for the treatment of high blood pressure. Instead, they are prescribed for conditions such as altitude sickness, glaucoma, metabolic alkalosis, or intracranial hypertension (e.g., pseudotumor cerebri).
The primary drug in this class is acetazolamide.
Common side effects include metabolic acidosis and, in some patients, allergic reactions.