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# Furosemide (Lasix)
## Overview
Furosemide is a potent loop diuretic that inhibits the reabsorption of sodium and chloride in the thick ascending limb of the loop of Henle, leading to increased excretion of water, sodium, chloride, potassium, calcium, and magnesium.
## Primary Indications
* Edema associated with heart failure, hepatic cirrhosis, and renal disease, including the nephrotic syndrome.
* Hypertension, usually used in combination with other antihypertensives.
## Adult Dosing
* **Edema:**
* Oral: Initial dose is typically 20-80 mg once daily. May be increased by 20-40 mg every 6-8 hours as needed. Doses may be given once daily, twice daily, or divided.
* Intravenous (IV) or Intramuscular (IM): Initial dose is typically 20-40 mg once daily. If ineffective, doses can be increased by 20 mg every 2 hours.
* **Maximum oral dose:** 600 mg/day.
* **Maximum IV/IM dose:** Generally 200 mg/day, though higher doses may be used in severe cases under close supervision. Continuous IV infusion may be considered for refractory edema.
* **Hypertension:**
* Oral: Initial dose is typically 40 mg twice daily. May be adjusted as needed.
* **Maximum dose:** Not established, but doses above 40 mg twice daily are not usually needed for this indication.
## Pediatric Dosing
* **Edema:**
* Oral: 1-2 mg/kg/dose once daily. May be increased by 1-2 mg/kg/dose every 6-8 hours.
* **Maximum oral dose:** 6 mg/kg/day.
* IV/IM: 1 mg/kg/dose once daily. May be increased by 1 mg/kg/dose every 2 hours.
* **Maximum IV/IM dose:** 6 mg/kg/dose.
* **Note:** Dosing may vary. Consult institutional guidelines or specialist recommendations for specific pediatric use, especially for neonatal or premature infants.
## Dose Adjustments
* **Renal Impairment:** Dosage may need to be increased in patients with renal impairment due to reduced GFR and impaired tubular secretion. However, monitor for ototoxicity, especially with rapid IV administration and high doses.
* **Hepatic Impairment:** Use with caution. Patients with cirrhosis may be more susceptible to electrolyte imbalances and azotemia.
* **Elderly:** May be more sensitive to the effects of furosemide; consider lower initial doses and slower titration.
## Contraindications
* Anuria.
* Hypersensitivity to furosemide or sulfonamides.
## Adverse Effects
* **Common:** Dizziness, lightheadedness, hypokalemia, hyponatremia, hypomagnesemia, dehydration, hypotension.
* **Serious:** Ototoxicity (hearing loss, tinnitus), hyperuricemia (gout), hyperglycemia, electrolyte imbalances, Stevens-Johnson syndrome, toxic epidermal necrolysis, aplastic anemia, thrombocytopenia, agranulocytosis.
## Key Drug Interactions
* **Aminoglycosides:** Increased risk of ototoxicity and nephrotoxicity.
* **Corticosteroids:** Increased risk of hypokalemia.
* **Digoxin:** Increased risk of digoxin toxicity due to furosemide-induced hypokalemia.
* **Lithium:** Reduced lithium clearance, increasing lithium toxicity.
* **NSAIDs:** May reduce furosemide's diuretic and antihypertensive effect.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Counteract potassium loss, but monitor for hyperkalemia.
* **Thiazide diuretics:** Additive diuretic effect.
## Monitoring
* **Electrolytes:** Serum electrolytes (sodium, potassium, chloride, magnesium, calcium) at baseline and periodically during therapy.
* **Renal function:** Serum creatinine and BUN.
* **Fluid balance:** Daily weights, intake and output.
* **Blood pressure:** Especially when used for hypertension.
* **Hearing:** Assess for tinnitus or hearing impairment.
## Clinical Pearls
* Administer IV furosemide slowly to reduce the risk of ototoxicity and hypotension. Avoid rapid IV push in high doses.
* Oral furosemide is best absorbed when taken on an empty stomach; however, if GI upset occurs, it can be taken with food or milk.
* Furosemide can cause photosensitivity; advise patients to use sun protection.
* Rapid IV administration can lead to transient hearing loss, which is usually reversible.
* Consider potassium supplementation or concurrent use of potassium-sparing diuretics if hypokalemia is significant or patient is symptomatic.
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**Disclaimer:** This information is intended for clinical use and does not substitute for professional medical advice. Always consult the most current prescribing information and relevant guidelines before making any treatment decisions.
