Furosemide

Benjamin Clanner-Engelshofen is a freelance writer in the medical department. He studied biochemistry and pharmacy in Munich and Cambridge / Boston (USA) and noticed early on that he particularly enjoyed the interface between medicine and science. That is why he went on to study human medicine.

More about the experts All content is checked by medical journalists.

The active ingredient furosemide belongs to the group of loop diuretics. It is used as a diuretic for high blood pressure, ascites and fluid retention in the tissue (edema) to remove the excess fluid from the body. Although furosemide was launched back in 1962, it is still the most powerful diuretic available. Here you can read everything you need to know about furosemide, side effects and use.

This is how furosemide works

The blood is filtered in the kidney. In the process, waste products, pollutants and also some medication are extracted and ultimately excreted in the urine. The smallest functional unit in the kidney is the nephron, which consists of the kidney corpuscle and a kidney tubule. Many of these nephrons are connected in parallel and filter small molecules out of the blood (blood proteins and blood cells remain in the blood). The resulting primary urine is not yet concentrated and is concentrated in the kidney tubules through the re-absorption of the water it contains. Other substances that are important for the body but have been filtered out (for example glucose, sodium, potassium and chloride ions) can also be reabsorbed into the blood.

The kidney tubule is divided into different sections, with furosemide acting in the so-called ascending part of the Henle loop (hence the name loop diuretic): Here it inhibits the re-uptake of sodium, potassium and chloride ions - they leave the body with the urine. Along with these charged particles, large amounts of water are also excreted, which is the actually intended furosemide effect. With high doses of furosemide, urine volumes of up to 50 liters per day are possible. The increased water excretion causes the blood pressure to drop.

Breakdown and excretion of furosemide

After ingestion, about two thirds of the active ingredient is absorbed from the intestine into the blood. The effect occurs after about half an hour. Only a small part of the active ingredient is metabolized in the liver (around ten percent), the rest is excreted unchanged - around a third in the stool, the rest in the urine. Half of the active ingredient is eliminated after about an hour.

When is furosemide used?

The active ingredient furosemide is used in:

• Retention of water in the body (edema) due to heart, kidney or liver disease
• impending kidney failure

Depending on the underlying disease, the active ingredient can be prescribed for short-term or long-term therapy.

This is how furosemide is used

Furosemide is mostly used in the form of sustained-release tablets or capsules. It is taken on an empty stomach in the morning with a glass of water. Higher dosages can also be divided into multiple doses throughout the day. Dosages of 40 to 120 milligrams of furosemide per day are usually sufficient; in individual cases and depending on the underlying disease, dosages of up to 500 milligrams per day can also be prescribed.

In high blood pressure therapy, furosemide is often combined with other antihypertensive agents in order to reduce the rate of side effects and increase effectiveness.

What are the side effects of furosemide?

Furosemide side effects such as electrolyte imbalances (especially changed sodium and potassium levels), lack of fluids, low blood volume and low blood pressure, increased blood lipid levels and increased creatinine levels in the blood are seen in more than one in ten patients.

In addition, every tenth to one hundredth patient has elevated cholesterol and uric acid levels in the blood, gout attacks and symptoms as a result of electrolyte disorders (calf cramps, loss of appetite, weakness, drowsiness, confusion, cardiac arrhythmias, etc.).

What should be considered when taking furosemide?

If other active ingredients such as glucocorticoids ("cortisone") or laxatives are taken during therapy with furosemide, this can lead to low blood potassium values. The same applies if larger quantities of liquorice are consumed.

Non-steroidal anti-inflammatory drugs (such as ASA), which are often used as headache relievers, for example, can weaken the furosemide effect. The same effect can occur with the combined use of phenytoin (in epilepsy) or substances that are also excreted via the kidney tubules such as probenecid (for gout) and methotrexate (for cancer and autoimmune diseases).

Caution is advised when simultaneously using drugs that act on the heart or trigger a certain cardiac arrhythmia (so-called QT time prolongation) as side effects. Because furosemide affects electrolyte concentrations, the effects of such drugs on the heart may be weaker or stronger. This is especially true for cardiac glycosides such as digoxin and digitoxin.

Simultaneous use with active substances that damage the kidneys or hearing (nephrotoxic or ototoxic effects) should be avoided. Examples of such active ingredients are antibiotics such as gentamycin, tobramycin, kanamycin and cancer drugs such as cisplatin.

The simultaneous intake of the mood stabilizer lithium should only be monitored closely, since lithium is transported in the body like sodium. In this way, its distribution in the body can change significantly.

During pregnancy, furosemide can be used for short periods under strict medical supervision. It crosses the placenta and passes into breast milk, which is why breastfeeding women should stop breastfeeding if necessary.

The active ingredient is also suitable for the treatment of children, but in a correspondingly reduced dosage. Since children under the age of six often have problems swallowing tablets, the oral solution should be used here.

How to get drugs with furosemide

The active ingredient furosemide requires a prescription in every dosage and can only be purchased in the pharmacy with a valid prescription.

How long has furosemide been known?

From 1919 poisonous mercury compounds were used as diuretics. The German company Hoechst finally developed the mercury-free active ingredient furosemide in 1959 and applied for a patent for it in 1962. It was soon used in practice.

Tags:  prevention hospital palliative medicine