Furosemide is a potent loop diuretic widely used in the management of fluid overload conditions such as edema associated with heart failure, liver cirrhosis, renal disorders, and also in hypertension. It acts on the thick ascending limb of the loop of Henle by inhibiting the reabsorption of sodium, potassium, and chloride ions, leading to increased urine output and rapid relief of excess fluid accumulation; because of this strong effect, it is often referred to as a “high-ceiling” diuretic. The drug was developed in the early 1960s by researchers at Hoechst AG and was introduced into clinical practice around 1964, where it quickly gained prominence due to its greater efficacy compared to earlier diuretics like thiazides. Over the decades, furosemide has remained a cornerstone of therapy in both acute and chronic settings and is recognized on the World Health Organization Model List of Essential Medicines, reflecting its importance, effectiveness, and widespread use in global healthcare.
BRAND NAMES
Furosemide, a loop diuretic commonly marketed as Lasix, is used to manage high blood pressure and fluid retention (edema) associated with conditions such as congestive heart failure, liver disease, or kidney disorders. Other brand names for furosemide include Furoscix, Diural, and Seguril.
MECHANISM OF ACTION
Furosemide is a powerful loop diuretic that works mainly by inhibiting the Na⁺-K⁺-2Cl⁻ symporter (NKCC2) in the thick ascending limb of the loop of Henle in the kidneys. This inhibition blocks the reabsorption of sodium, chloride, and potassium, leading to increased excretion of water, sodium, chloride, magnesium, and calcium.
PHARMACOKINETICS
Absorption: Rapidly absorbed from the stomach, with oral peak plasma concentrations reached within 1–2 hours.
Distribution: Volume of distribution (VdVdVd) ranges from 0.07 to 0.2 L/kg. Furosemide is 91%–99% protein-bound, mainly to albumin.
Metabolism: Approximately 10% is metabolized in the liver, with additional metabolism in the kidneys to an active glucuronide.
Elimination: Primarily excreted via active renal tubular secretion. The half-life is 1–2 hours in healthy individuals but may extend up to 24 hours in cases of severe kidney impairment.
PHARMACODYNAMICS
Furosemide is a powerful loop diuretic that blocks the (\text{Na}^{+})-(\text{K}^{+})-(2\text{Cl}^{-}) cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, preventing the reabsorption of sodium, chloride, and water. This results in rapid diuresis and natriuresis, decreases edema and plasma volume, and increases the excretion of calcium and magnesium.
ADMINISTRATION
Furosemide is a loop diuretic available in oral tablets (20–80 mg), oral solution (10 mg/mL), and IV/IM injection (10 mg/mL) formulations, used to manage edema and high blood pressure. Oral doses are typically given 1–2 times daily, preferably in the morning, with or without food, but should be taken consistently. Intravenous doses must be administered slowly over 1–2 minutes to minimize the risk of toxicity.
DOSAGE AND STRENGTH
Furosemide is available as oral tablets (20–80 mg), an oral solution (10 mg/mL), and IV/IM injections (10 mg/mL). Oral doses are usually administered 1–2 times daily, preferably in the morning, with or without food. Intravenous doses should be given slowly over 1–2 minutes to reduce the risk of toxicity. It is used to treat edema and hypertension.
DRUG INTERACTIONS
Furosemide (Lasix) can interact with various medications, including NSAIDs, lithium, and antihypertensive drugs, which may increase the risk of kidney damage, excessive blood pressure reduction, and ototoxicity (hearing loss). As a loop diuretic that lowers potassium levels, it should be used cautiously with drugs that affect electrolyte balance.
FOOD INTERACTIONS
Furosemide (Lasix) has important dietary considerations, including limiting high-sodium foods, which can reduce its diuretic effectiveness, and monitoring potassium intake to prevent deficiency. Alcohol and excessive caffeine should be minimized, as they may contribute to dizziness and electrolyte imbalances. Taking furosemide on an empty stomach is generally recommended, since food can decrease its absorption.
CONTRAINDICATIONS
Furosemide is contraindicated in patients with anuria (inability to urinate), known hypersensitivity to furosemide or sulfonamides, severe electrolyte imbalances, and hepatic coma. It should be avoided in severe liver disease, and used with caution or discontinued in cases of severe renal impairment.
SIDE EFFECTS
Increased urination
Dizziness
Headache
Electrolyte imbalances (low potassium, sodium, magnesium)
OVER DOSE
A furosemide (Lasix) overdose can result in excessive loss of water and electrolytes, causing severe dehydration, hypotension, and dangerous imbalances of potassium, sodium, and chloride. Immediate medical attention is essential if an overdose is suspected, as it may lead to kidney failure, dizziness, fainting, or irregular heart rhythms.
TOXICITY
Furosemide toxicity typically arises from excessive diuretic use, leading to severe dehydration, low blood volume (hypovolemia), and significant electrolyte disturbances such as hypokalemia. Symptoms of overdose may include extreme thirst, irregular heartbeat, muscle weakness, confusion, and dizziness. Treatment focuses on restoring fluids and electrolytes, while severe toxicity remains uncommon.
