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## Furosemide (Lasix)
### Overview
Furosemide is a potent loop diuretic used to treat edema associated with heart failure, cirrhosis, and renal disease, as well as hypertension. It inhibits the Na-K-2Cl symporter in the thick ascending limb of the loop of Henle, leading to increased excretion of sodium, chloride, potassium, and water.
### Primary Indications
* Edema due to heart failure, liver disease, or renal disease.
* Hypertension (used as a component of antihypertensive therapy).
### Adult Dosing
* **Edema:**
* **Oral:** Starting dose is typically 20-80 mg once or twice daily. May be increased by 20-40 mg every 6-8 hours as needed. Doses as high as 600 mg/day have been used in severe cases, but higher doses are generally not more effective and increase the risk of adverse effects.
* **Intravenous (IV) or Intramuscular (IM):** Starting dose is typically 20-40 mg once. May be increased by 20 mg every 2 hours as needed. The IV dose is generally about half the oral dose.
* **Hypertension:**
* **Oral:** Starting dose is typically 40 mg twice daily. Doses are adjusted based on blood pressure response.
* **Intermittent IV infusion for acute decompensated heart failure:** Dosing is highly individualized and dependent on prior oral diuretic regimen and clinical response. Initial doses may range from 40-80 mg IV, with subsequent doses adjusted based on urine output and symptom improvement.
### Pediatric Dosing
* **Edema:**
* **Oral:** 1-2 mg/kg/dose every 6-12 hours. Maximum dose: 6 mg/kg/day.
* **IV or IM:** 1 mg/kg/dose every 6-12 hours. Maximum dose: 6 mg/kg/day. Neonates may have altered pharmacokinetics; doses may need to be adjusted.
### Dose Adjustments
* **Renal Impairment:** Dose may need to be increased in renal insufficiency due to impaired renal excretion. However, monitor closely for electrolyte imbalances and ototoxicity.
* **Hepatic Impairment:** Dose may need to be reduced in patients with severe hepatic cirrhosis due to increased bioavailability and risk of hepatic encephalopathy.
### Contraindications
* Anuria.
* Known hypersensitivity to furosemide or sulfonamides (cross-sensitivity is possible).
* Electrolyte depletion (e.g., hypokalemia, hyponatremia).
### Adverse Effects
* **Common:** Dizziness, lightheadedness, headache, electrolyte imbalances (hypokalemia, hyponatremia, hypochloremia, hypomagnesemia, hypocalcemia), dehydration, hypotension.
* **Serious:** Ototoxicity (especially with rapid IV administration or high doses), rash, Stevens-Johnson syndrome, photosensitivity, hyperglycemia, hyperuricemia (gout), pancreatitis, aplastic anemia, thrombocytopenia.
### Key Drug Interactions
* **Aminoglycosides:** Increased risk of ototoxicity and nephrotoxicity.
* **NSAIDs:** May reduce the diuretic and antihypertensive effects of furosemide.
* **ACE inhibitors/ARBs:** Increased risk of hypotension and renal dysfunction.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Monitor potassium levels closely to prevent hyperkalemia.
* **Digoxin:** Increased risk of digoxin toxicity due to furosemide-induced hypokalemia.
* **Lithium:** Increased risk of lithium toxicity due to decreased renal clearance.
* **Corticosteroids:** Increased risk of electrolyte depletion.
### Monitoring
* **Electrolytes:** Monitor serum electrolytes (sodium, potassium, chloride, magnesium, calcium) frequently, especially at initiation and dose changes, and in patients with risk factors.
* **Renal function:** Monitor BUN and serum creatinine.
* **Fluid balance:** Monitor intake and output, weight.
* **Blood pressure:** Monitor for hypotension.
* **Hearing:** Assess for tinnitus or hearing loss.
* **Blood glucose and uric acid:** Consider monitoring in susceptible patients.
### Clinical Pearls
* Furosemide's effect is dose-dependent. For edema, dosing is often guided by urine output.
* Rapid IV administration (>4 mg/min) can increase the risk of ototoxicity. Administer IV furosemide as a slow infusion.
* Oral and IV doses are not always directly interchangeable; IV doses are typically lower.
* Administering furosemide in the morning can help minimize nocturia.
* Patients on furosemide should be advised to maintain adequate fluid intake and report symptoms of dehydration or electrolyte imbalance (e.g., muscle cramps, dizziness).
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*This information is intended for clinical use and does not substitute for professional medical advice. Always verify current prescribing information and consult with a healthcare professional for patient-specific guidance.*
