Diuretics are drugs used to regulate fluid balance in the body. They work by increasing urine output and decreasing urine excretion. These medications are sometimes prescribed for patients with high blood pressure or kidney disease. There are many different kinds of diuretics available today, but they all have one thing in common: they increase urine production (via increased water retention) and decrease urination (via decreased water loss). Some diuretics act directly on the kidneys, while others affect other organs such as the heart and lungs.
The main purpose of diuretics is to maintain a normal urine volume when there is excess fluid in the body (for example during exercise), or when fluid levels are low (such as due to dehydration). For example, if a person drinks too much water after exercising, their urine volume will rise because they’ve stored extra water in the body.
If they drink less than usual fluids, their urine volume will fall. When the kidneys expel some of these excess fluid from the body through urination, it causes a drop in blood pressure.
Diuretics may be prescribed for any condition where excessive fluid is being lost (e.g., pregnancy).
In the treatment of hypertension (high blood pressure), diuretics are not the first line of treatment, as there are many more effective classes of high-blood-pressure drugs. However, they are still used to combat the excess fluid along with the increased blood volume that results from the high-blood-pressure. This is sometimes known as “water pills” or “aquaretics.”
There are several classes of diuretics:
The following examples are potassium-sparing diuretics, which prevent the loss of potassium ions (and not sodium ions) while promoting the excretion of excess fluid through the production of urine.
Thiazides, which include hydrochlorothiazide (HCTZ), chlorothiazide, and chlorthalidone
loop diuretics, which include furosemide (Lasix), bumetanide, and ethacrynic acid
chlortalidone, which does not promote the excretion of potassium ions like the thiazides and is therefore referred to as a “non-potassium-sparing” diuretic
Carbonic anhydrase inhibitors, which include dichlorophenamide and the more common acetazolamide
The following examples are “sodium-sparing” diuretics, which prevent the loss of sodium ions (and not potassium ions) while promoting the excretion of excess fluid through the production of urine.
The following examples are osmotic diuretics, which work by promoting water flow from within the cells via osmosis, through pores in the cell membrane. The main difference between this class and loop diuretics is that the loop diuretics cause an increase in urine production by creating a “reservoir” in certain parts of the nephrons while stimulating the excretion of urine from other parts.
Osmotic diuretics have a limited effect when compared to loop diuretics and other classes.
The following examples are carbonic anhydrase inhibitors, which work by inhibiting the enzyme carbonic anhydrase, which regulates the equilibrium of carbon dioxide and water. This leads to increased excretion of bicarbonate (which is converted to hydrogen ions and thus increases the acidity of urine) and other ions.
Bicarbonate is the primary buffer in the blood, so when its concentration in urine is increased, it reduces the blood’s pH (makes it more acidic). This causes a decrease in the blood’s ability to transport oxygen.
The primary reason for taking this class of diuretics is to treat glaucoma, especially in those who are intolerant to the other classes of drugs or have contraindications to them (such as impaired liver or kidney function).
Diuretics are used in the treatment of hypertension (high blood pressure), edema (fluid retention), heart failure, and nephrotic syndrome.
They are also used to prevent renal complications in people with diabetes,to reduce elevated intracranial pressure (elevated pressure within the skull) in those with acute head injuries, and to treat ascites (a build up of fluid within the peritoneum) in those with liver failure.
Diuretics are frequently used as a doping agent in sports, to assist athletes in losing weight quickly.
Common diuretics include:
There are a number of factors that can influence the effectiveness of diuretics and their potential to cause harmful effects. The most important factor is how much fluid is being removed from the body.
For example, when a person is drinking large amounts of fluid, then a diuretic will have less of an effect because there is already a high concentration of fluid in the body. In contrast, a person who is drinking very little will experience much greater effects from a diuretic since the concentration of fluid in their body is low.
A common side effect of diuretics is dehydration, which occurs when a person produces more urine than they take in (i.e.
water) through food or drink. This can result in many effects including cramping, nausea, headaches, dizziness and dry skin. More severe cases can lead to reduced concentration, irritability and confusion.
Increased excretion of potassium can cause muscle weakness and heart rhythm disturbances.
In some people, diuretics cause the kidneys to lose the ability to produce varying concentrations of urine. This leads to a condition called oliguria where the urine output is less than 400 ml within a 24-hour period.
Many loop diuretics, such as furosemide, cause the loss of calcium in the urine. For this reason they are only recommended for people who need to lose large amounts of fluid and those with relatively normal kidney function as otherwise kidney damage occurs.
The following diuretics have been known to cause the following medical problems:
The following table shows approximate percentages of excretion for various substances.
Many herbal remedies have similar properties to diuretics, but little is known about their potential long term safety.
Drugs that affect the kidney’s ability to produce urine are called antidiuretic drugs. These tend to have the opposite effect of diuretics and are used to treat some of the conditions listed above (no specific ones listed).
An osmotic diuretic is a substance that draws water into the intestines, which is then excreted from the body. Osmotic diuretics include glycerin, magnesium salts and potassium salts.
They are used to treat bloating and difficult or infrequent bowel movements.
Sources & references used in this article:
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Metoprolol versus thiazide diuretics in hypertension. Morbidity results from the MAPHY Study. by J Wikstrand, I Warnold, J Tuomilehto, G Olsson… – …, 1991 – Am Heart Assoc
Beta-blockers or diuretics in hypertension? A six year follow-up of blood pressure and metabolic side effects by G Berglund, O Andersson – The Lancet, 1981 – Elsevier
Diuretics for hypertension: a review and update by GC Roush, DA Sica – American journal of hypertension, 2016 – academic.oup.com
Diuretics for hypertension by LR Krakoff – Circulation, 2005 – Am Heart Assoc
Diuretics in hypertension by ED Frohlich – 1987 – journals.lww.com
Combination therapy with ACE inhibitors/angiotensin II receptor antagonists and diuretics in hypertension by B Waeber – Expert Review of Cardiovascular Therapy, 2003 – Taylor & Francis
The evidence-based use of thiazide diuretics in hypertension and nephrolithiasis by RF Reilly, AJ Peixoto, GV Desir – … Journal of the American Society of …, 2010 – Am Soc Nephrol