Furosemide
2 medicines
Furosemide is a loop diuretic that makes the kidneys pass out extra salt and water, used for fluid overload in heart failure, liver and kidney disease. It can cause serious dehydration and dangerously low potassium, so blood tests are needed to check electrolytes and kidney function.
Key facts
- Furosemide (also sold as Lasix) is a potent loop diuretic. It blocks salt reabsorption in the kidney's loop of Henle, so the body passes out more water and sodium as urine.
- It treats fluid buildup from heart failure, kidney disease, liver disease and pulmonary edema. Onset is fast, within an hour by mouth and within minutes by injection.
- Furosemide causes significant loss of potassium, sodium and other electrolytes along with fluid. This can cause dangerous dehydration, low blood pressure and an irregular heartbeat, so blood tests to check electrolytes and kidney function are required during treatment.
- Seek urgent care for severe dizziness, a fast or irregular heartbeat, extreme thirst, or a sudden drop in urine output.
What furosemide treats
Furosemide treats fluid overload (edema) caused by heart failure, chronic kidney disease, liver cirrhosis with ascites, and pulmonary edema. It is also used, alongside other medicines, to lower blood pressure. It does not cure any of these conditions; it manages the fluid buildup they cause.
How furosemide works
The kidneys normally reabsorb sodium and chloride in a segment called the loop of Henle. Furosemide blocks this reabsorption, so more sodium, chloride and water stay in the urine and leave the body. This reduces the volume of fluid in the bloodstream and tissues, easing swelling and the strain on the heart and lungs.
Before you take it
- Do not take furosemide if you cannot pass urine, or if you have had a severe allergic reaction to it.
- Tell your prescriber about kidney or liver disease, gout, diabetes, hearing problems, and all other medicines, especially other diuretics, blood-pressure drugs, NSAIDs, aminoglycoside antibiotics, digoxin and lithium.
- Furosemide increases urination, so avoid taking a dose late in the day unless directed.
Side effects
Common effects include increased urination, thirst, dizziness on standing, and muscle cramps.
Stop and seek urgent medical care for:
- Extreme thirst, a very dry mouth or confusion (severe dehydration).
- Muscle cramps, weakness or an irregular heartbeat (low potassium or other electrolyte loss).
- Sudden hearing loss or ringing in the ears, especially with high or rapid intravenous doses.
- A sudden severe skin reaction or signs of an allergic reaction.
Safety essentials
- Furosemide's defining risk is electrolyte loss and dehydration. Your prescriber will check your blood sodium, potassium and kidney function regularly, more often at the start of treatment or after a dose change.
- During illness with vomiting, diarrhea or reduced fluid intake, dehydration risk rises sharply; tell your prescriber if you become unwell, as your dose may need to pause.
- Avoid NSAIDs where possible, since they blunt furosemide's effect and add to kidney strain; combining furosemide with lithium can raise lithium to toxic levels.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.