Diuretics l Diuretic drugs l Uses of Diuretic drugs

They may be indicated for people who suffer from edema, an intense accumulation of fluids in the body’s tissues, and those who suffer from high blood pressure or other heart related diseases. Increasing the production of urine not only releases fluid, but also helps rid the body of excess salts and may reduce blood volume

A diuretic is any drug that elevates the rate of urination and thus provides a means of forced diuresis. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.

Types of Diuretics

Loop diuretics have this ability, and are therefore often synonymous with high ceiling diuretics. Loop diuretics, such as furosemide, inhibit the body’s ability to reabsorb sodium at the ascending loop in the kidney which leads to a retention of water in the urine as water normally follows sodium back into the extracellular fluid (ECF). Other examples of high ceiling loop diuretics include ethacrynic acid, torsemide and bumetanide.

High ceiling diuretics are diuretics that may cause a substantial diuresis – up to 20% of the filtered load of NaCl and water. This is huge when compared to normal renal sodium reabsorption which leaves only ~0.4% of filtered sodium in the urine.

Thiazides, Drugs such as hydrochlorothiazide act on the distal convoluted tubule and inhibit the Sodium-chloride symporter leading to a retention of water in the urine as water normally follows penetrating solutes.

Potassium-sparing diuretics: These are diuretics which do not promote the secretion of potassium into the urine; thus, potassium is spared and not lost as much as in other diuretics. The term “potassium-sparing” refers to an effect rather than a mechanism or location; nonetheless, the term almost always refers to two specific classes that have their effect at similar locations:

Aldosterone antagonists: Spironolactone, which is a competitive antagonist of aldosterone. Aldosterone normally adds sodium channels in the principal cells of the collecting duct and late distal tubule of the nephron. Spironolactone prevents aldosterone from entering the principal cells, preventing sodium reabsorption. A similar agent is potassium canreonate.

Epithelial sodium channel blockers: amiloride and triamterene.

Calcium-sparing diuretics: The term “calcium-sparing diuretic” is sometimes used to identify agents that result in a relatively low rate of excretion of calcium.

The reduced concentration of calcium in the urine can lead to an increased rate of calcium in serum. The sparing effect on calcium can be beneficial in hypocalcemia, or unwanted in hypercalcemia.

The thiazides and potassium-sparing diuretics are considered to be calcium-sparing diuretics.

• The thiazides cause a net decrease in calcium lost in urine.
• The potassium-sparing diuretics cause a net increase in calcium lost in urine, but the increase is much smaller than the increase associated with other diuretic classes.

By contrast, loop diuretics promote a significant increase calcium excretion. This can increase risk of reduced bone density.

Osmotic diuretics: Compounds such as mannitol are filtered in the glomerulus, but cannot be reabsorbed. Their presence leads to an increase in the osmolarity of the filtrate. To maintain osmotic balance, water is retained in the urine.

Glucose, like mannitol, is a sugar that can behave as an osmotic diuretic. Unlike mannitol, glucose is commonly found in the blood. However, in certain conditions such as diabetes mellitus, the concentration of glucose in the blood exceeds the maximum reabsorption capacity of the kidney. When this happens, glucose remains in the filtrate, leading to the osmotic retention of water in the urine. Use of some drugs, especially stimulants may also increase blood glucose and thus increase urination.

Low ceiling diuretics: The term “low ceiling diuretic” is used to indicate that a diuretic has a rapidly flattening dose effect curve (in contrast to “high ceiling”, where the relationship is close to linear). It refers to a pharmacological profile, not a chemical structure. However, there are certain classes of diuretic which usually fall into this category, such as the thiazides

Adverse effects
The main adverse effects of diuretics are hypovolemia, hypokalemia, hyperkalemia, hyponatremia, metabolic alkalosis, metabolic acidosis and hyperuricemia. Each are at risk of certain types of diuretics and present with different symptoms.