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# Furosemide (Lasix)
## Overview
Furosemide is a potent loop diuretic that inhibits the Na+-K+-2Cl- symporter in the thick ascending limb of the loop of Henle. It promotes rapid diuresis and natriuresis.
## Primary Indications
* Edema associated with congestive heart failure (CHF), hepatic cirrhosis, and renal impairment.
* Hypertension (adjunctive therapy, though less common than thiazides).
## Adult Dosing
* **Edema:** Initial dose 20–80 mg orally once daily. If response is inadequate, increase in 20–40 mg increments every 6–8 hours until desired effect is achieved.
* **Maintenance:** Dosing is titration-dependent; monitor weight and volume status.
* **Maximum Dose:** Generally 600 mg/day (rarely required; requires specialist oversight).
## Pediatric Dosing
* **Initial dose:** 1–2 mg/kg/dose orally once or twice daily.
* **Titration:** Increase by 1 mg/kg/dose no more frequently than every 6–8 hours.
* **Maximum Dose:** 6 mg/kg/dose; not to exceed 6 mg/kg/day total.
## Dose Adjustments
* **Renal Impairment:** Higher doses may be required in severe chronic kidney disease (CKD) due to reduced secretion into the tubular lumen.
* **Hepatic Impairment:** Use with caution; rapid shifts in fluid/electrolytes may precipitate hepatic encephalopathy.
## Contraindications
* Anuria.
* Hypersensitivity to furosemide or sulfonamides (though cross-reactivity is clinically debated).
* Severe electrolyte depletion (hypokalemia, hyponatremia).
* Hepatic coma or severe electrolyte depletion states.
## Adverse Effects
* **Common:** Hypokalemia, hypomagnesemia, hyponatremia, dehydration, hypotension.
* **Rare/Serious:** Ototoxicity (dose-dependent, usually with rapid IV push), photosensitivity, hyperuricemia (gout), hyperglycemia.
## Key Drug Interactions
* **Aminoglycosides:** Increased risk of ototoxicity and nephrotoxicity.
* **NSAIDs:** May reduce natriuretic effect and increase risk of acute kidney injury.
* **Lithium/Digoxin:** Furosemide-induced electrolyte disturbances (hypokalemia) increase risk of digoxin toxicity; loop diuretics may reduce lithium clearance (toxicity risk).
## Monitoring
* **Baseline:** Serum electrolytes (K+, Mg2+, Na+), BUN/Creatinine, blood pressure, weight.
* **Ongoing:** Daily weight monitoring, serum electrolytes as clinically indicated (especially during titration), and renal function.
## Clinical Pearls
* **Diuretic Resistance:** If response is poor, consider evaluating dietary sodium intake or switching from once-daily to twice-daily dosing to prevent "rebound" sodium retention.
* **Administration:** May be taken with food to minimize GI upset. If dose is >40 mg/day, split dosing is often preferred to mimic physiological response.
* **Efficacy:** The diuretic action persists even in patients with reduced GFR, making it superior to thiazides in renal impairment.
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**Disclaimer:** This information is for educational purposes only. Prescribing practices vary by institution and patient-specific factors. Always verify current prescribing information via official pharmacy references (e.g., Lexicomp, Micromedex) or clinical guidelines before administration.
