Furosemide is a loop diuretic drug whose main indication is the treatment of high blood pressure.
Furosemide is a diuretic of maximum efficacy that belongs to the classification of loop diuretics. These drugs are capable of altering the ion transport along the nephron, which is the anatomical and physiological unit of the kidney.
By altering this transport, they increase the urine volume since they stimulate the renal excretion of water and electrolytes. All this causes a decrease in the volume of extracellular fluids.
It is a drug that is indicated alone or in combination when the patient suffers from high blood pressure . However, it can also be used to treat edemas (due to fluid retention) caused by various medical problems such as liver or heart disease. To better understand how furosemide works in our body, we must understand how our kidney works.
Mechanism of ion transport in the kidney
The kidneys are the main organs of the urinary system. They are responsible for the excretion of waste substances through the formation of urine and maintain the balance of the internal environment of the body, ie, homeostasis.
Its anatomical and physiological unit is the nephron , and it consists of 4 parts: the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and the collecting tubule.
The liquid to be purified reaches the proximal convoluted tubule passing through the glomerulus. This tube is very permeable to water and is where most of the drugs are actively secreted so that they are eliminated by urine. Then, the remaining liquid passes to the loop of Henle, which consists of two parts, the descending and ascending.
The descending part is also permeable to water but is totally impermeable to solutes. Therefore, due to these characteristics, a hypertonic urine will be formed , that is, with a high concentration of solutes. As for the ascending part, it has the opposite characteristics, is impermeable to water and permeable to solutes, originating hypotonic urine.
This urine passes into the distal convoluted tubule, which is impermeable to water and forms hypotonic urine. Finally, the liquid reaches the collecting tubule, where the water permeability is variable. The control of the processes at this level is mediated by the hormone aldosterone and the antidiuretic hormone (ADH).
When the urine is formed, it reaches through the ureters to the bladder , which, when it reaches a certain level of filling, sends a signal to the brain that creates the need to urinate.
Mechanism of action of furosemide
This drug acts from within the loop of Henle, that is, in the tubular lumen. To get here, it is secreted in the proximal convoluted tubule by active transport or by passive diffusion .
Active transport is a type of exchange of substances in the body that requires energy, unlike simple diffusion, which does not need any energy source.
Once in the loop of Henle, it inhibits the transporter of sodium, potassium and chloride, and to a lesser extent calcium and magnesium. This action is carried out in the ascending handle, which is the thinning part, since it is permeable to water.
By blocking these cotransporters, it prevents these electrolytes from being reabsorbed, causing more water to be released to try to dilute it. The effects of furosemide are rapid and of short duration. By eliminating more water, reduces its volume in the body due to this phenomenon its antihypertensive effects .
Furosemide can be administered both orally and intravenously . If the first option is chosen, the effects last between 4 and 8 h, observing the action at 10-30 minutes. If the second option is chosen, the effects can be observed after 5 minutes and last approximately 2 hours.
It has a bioavailability of 90% and has a partial metabolism in the liver , where 4-chloro-5-sulfamoyl-antralinic acid is formed which, with the rest of the drug, will be eliminated in the urine.
It is important to note that it binds to a high degree to plasma proteins , a fact to be taken into account if furosemide is being administered with any other drug that has the same characteristic, since they can interact and cause undesirable effects.
The different adverse effects that furosemide can trigger are due to its diuretic effects . Among them we can point out:
- Hypokalemia When the doses are high, potassium levels in the blood can decrease a lot and can trigger arrhythmias .
- Hypochloremic alkalosis.
- Hypovolemia, hyponatremia, hyperuricemia and hyperglycemia.
- Ototoxicity (problems in the ears).