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# Furosemide (Lasix)
## Overview
Furosemide is a loop diuretic that inhibits the Na-K-2Cl symporter in the thick ascending limb of the loop of Henle, leading to potent diuresis and natriuresis.
## Primary Indications
* Edema associated with congestive heart failure (CHF)
* Cirrhosis of the liver
* Renal disease, including nephrotic syndrome
* Hypertension (often as adjunctive therapy)
## Adult Dosing
* **Edema:**
* **Oral:** Start with 20-80 mg once daily. If needed, dose can be increased by 20-40 mg every 6-8 hours. Typical doses range from 20-80 mg daily, but can go up to 600 mg daily in severe cases, divided into doses.
* **Intravenous (IV) or Intramuscular (IM):** Start with 20-40 mg once daily. If needed, dose can be increased by 20 mg every 2 hours. Equivalent to oral dose at a 1:1 ratio, but IV may be more potent; consider a 1:2 ratio (IV:PO) initially in some patients. Maximum IV dose typically 100-200 mg per dose, but higher doses may be used under specialist supervision.
* **Hypertension:**
* **Oral:** Start with 40 mg twice daily. May be increased to 80-120 mg daily in divided doses. Not usually a first-line agent for hypertension.
## Pediatric Dosing
* **Edema:**
* **Oral:** 1-2 mg/kg/dose every 6-12 hours. Maximum dose 6 mg/kg/dose.
* **Intravenous (IV) or Intramuscular (IM):** 1 mg/kg/dose every 6-12 hours. Maximum dose 6 mg/kg/dose.
## Dose Adjustments
* **Renal Impairment:** Dose requires careful titration. Patients with severe renal impairment may require higher doses due to decreased protein binding and reduced tubular secretion. Oral bioavailability can be reduced in renal failure, potentially requiring IV administration or higher oral doses.
* **Hepatic Impairment:** Dose may need to be reduced due to altered pharmacokinetics and increased sensitivity to fluid and electrolyte losses.
## Contraindications
* Anuria
* Hypersensitivity to furosemide or sulfonamides (caution advised)
* Severe electrolyte depletion (e.g., hypokalemia, hyponatremia)
## Adverse Effects
* **Common:** Dizziness, lightheadedness, hypotension, dehydration, electrolyte imbalance (hypokalemia, hyponatremia, hypochloremia), hyperglycemia, hyperuricemia.
* **Less Common:** Ototoxicity (especially with rapid IV infusion or high doses), rash, photosensitivity, gastrointestinal upset, muscle cramps.
* **Rare:** Agranulocytosis, aplastic anemia, pancreatitis, hepatic dysfunction.
## Key Drug Interactions
* **Aminoglycosides/Other Ototoxic Drugs:** Increased risk of ototoxicity.
* **NSAIDs:** May reduce diuretic and antihypertensive effects; increase risk of renal impairment.
* **ACE Inhibitors/ARBs:** Increased risk of hypotension and renal dysfunction, especially in volume-depleted patients.
* **Corticosteroids:** Increased risk of hypokalemia.
* **Digoxin:** Increased risk of digoxin toxicity due to furosemide-induced hypokalemia.
* **Lithium:** Reduced lithium clearance, increasing risk of lithium toxicity.
* **Thiazide Diuretics:** Additive effects on diuresis and electrolyte depletion.
## Monitoring
* **Electrolytes:** Sodium, potassium, chloride, magnesium, calcium (especially at initiation and with dose changes).
* **Renal Function:** Serum creatinine, BUN.
* **Fluid Balance:** Intake and output, daily weights.
* **Blood Pressure:** Monitor for hypotension.
* **Auditory Function:** Assess for tinnitus or hearing loss, particularly with high doses or rapid IV administration.
* **Glucose:** Monitor in diabetic patients.
## Clinical Pearls
* Administer oral furosemide with food or milk to minimize GI upset.
* For IV administration, infuse slowly (over 30-60 minutes) to reduce the risk of ototoxicity. Rapid IV push is generally discouraged.
* Diuresis may be less effective in patients with significant renal impairment or in those taking NSAIDs.
* Monitor for signs of dehydration and electrolyte imbalance, especially in elderly patients or those on other diuretics or medications affecting fluid/electrolytes.
* Consider potassium supplementation or potassium-sparing diuretics if hypokalemia is persistent or symptomatic.
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*Please consult the most current prescribing information and relevant institutional protocols for definitive dosing and management guidelines. This information is intended for healthcare professionals and should not be used as a substitute for professional medical advice.*
