Furosemide: Effects, Uses & Risks

Furosemide is the name given to a loop diuretic. The drug has a diuretic effect and is used for edema or high blood pressure.

What is furosemide?

The active ingredient furosemide belongs to the drug group of loop diuretics. These have the property of excreting larger amounts of tissue fluid from the body, which is done by inhibiting a transport protein in the kidney. Diuretic drugs were already being used in 1919 in the form of toxic mercury compounds. It was not until 1959 that the German company Hoechst developed an active ingredient called furosemide that was free of mercury. The application for the furosemide patent was filed in 1962, and the drug was soon in use. To this day, furosemide remains one of the most potent diuretic drugs.

Pharmacological action

Furosemide exhibits a potent and rapid onset of action. This is achieved by blocking the transport protein Na-K-2Cl cotransporter within the kidney or the ascending portion of the loop of Henle. Due to the blockade, there is inhibition of reabsorption of water, chloride, sodium and potassium. In this way, more urine is formed, which is then excreted more. This in turn leads to a rapid reduction of water retention in the body tissues. Depending on the dose used, furosemide can stimulate hormonal control of urine excretion. This effect is important in the treatment of kidney dysfunction. Furosemide is also able to lower high blood pressure. For this purpose, the drug stimulates the excretion of common salt (sodium). Because furosemide also dilates the blood vessels, it can be used to stimulate blood flow to the kidneys. In the case of cardiac insufficiency, furosemide provides relief for the heart. Thus, the dilatation of the veins achieves a decrease in pressure, which has a negative effect on the heart. If furosemide is administered intravenously, large amounts of water, up to 50 liters per day, can leave the organism. About two-thirds of the loop diuretic is absorbed into the blood via the intestines. Around 10 percent of the active substance is metabolized by the liver. The remaining amount is excreted by the body without any changes, which takes place in the stool and urine. After about 60 minutes, about 50 percent of the furosemide has left the body.

Medical use and application

The uses of furosemide include the treatment of edema (water retention in the tissues) due to heart disease, high blood pressure, liver disease such as cirrhosis, kidney dysfunction, a watery belly (ascites), or severe burns. In addition, furosemide can be used to treat pulmonary edema because it flushes out fluid quickly and effectively. The loop diuretic is also considered useful in preventing acute kidney failure. Furosemide can be used both in the short term and as part of long-term therapy. In most cases, the drug is administered in the form of tablets or capsules that release the active ingredient with a delay. Infusion is also possible. The tablets are taken in the morning on an empty stomach with water. Higher dosages can be spread throughout the day and taken several times. The recommended dose varies between 40 and 120 milligrams a day. In some cases, however, a dose of up to 500 milligrams may be appropriate. If treatment is given for high blood pressure, furosemide is usually combined with other antihypertensive drugs. Through this process, the effectiveness increases and side effects are reduced.

Risks and side effects

About one in ten patients experience adverse side effects after taking furosemide. These primarily include drowsiness, apathy, blood pressure fluctuations with changes in body position, thirst, loss of appetite, increased excretion of urine, muscle weakness, cardiac arrhythmias, nerve insensitivity, partial paralysis, and flatulence. Furthermore, marked skin inflammation, redness, rashes, sensitivity to light and convulsions may occur. In rare cases, dizziness, head pressure, muscle tension, dry mouth, hearing disorders, gastrointestinal problems, anemia, gout attacks (in case of pre-existing conditions), itching, and inflammation of the pancreas may also occur.In the worst case, furosemide can cause low blood volume, dehydration of the body, and circulatory collapse. In the elderly, the development of thrombosis is also possible. Contraindications to furosemide include severe potassium depletion in the blood, marked liver dysfunction associated with loss of consciousness, renal dysfunction in which there is a lack of urine production, and hypersensitivity to the drug or chemically related substances such as trimethoprim or sulfonamides. If the patient suffers from gout, diabetes mellitus (diabetes), constricted coronary arteries, protein deficiency, urinary outflow disorders, circulatory disorders of cerebral vessels, renal dysfunction, and liver shrinkage, he or she must take special care during furosemide therapy. In case of urinary outflow obstruction, free outflow of urine should be ensured, otherwise there is a risk of overdistension of the urinary bladder. During pregnancy, it is recommended to take furosemide only in exceptional cases. Treatment should not be prolonged. In animal studies, for example, furosemide caused damage to embryos. Since the active ingredient has a negative effect on the blood supply to the placenta and uterus, growth disorders of the child cannot be ruled out. Furosemide must not be taken during breastfeeding, as the drug passes into breast milk, which in turn causes damage to the baby. In premature births, there is a risk of kidney stone formation in the child due to the administration of furosemide. For this reason, the kidneys must be checked regularly by ultrasound examinations by a doctor.