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# Lasix (furosemide)
## Overview
Furosemide is a potent loop diuretic that inhibits the Na-K-2Cl symporter in the thick ascending limb of the loop of Henle, promoting the excretion of sodium, chloride, and water. It has a rapid onset (oral: 30–60 minutes) and a duration of action of approximately 6–8 hours.
## Primary Indications
* Edema associated with congestive heart failure (CHF), hepatic cirrhosis, and renal impairment (including nephrotic syndrome).
* Hypertension (adjunctive therapy).
## Adult Dosing
* **Edema:** Initial dose 20–80 mg orally once daily. If response is inadequate, titrate carefully in increments of 20–40 mg at intervals of 6–8 hours.
* **Hypertension:** 20–40 mg orally twice daily.
* **Maximum:** Doses up to 600 mg daily have been used in severe edema, but clinical judgment is critical to avoid profound volume depletion and electrolyte disturbances.
## 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 based on response.
* **Maximum:** 6 mg/kg/dose.
## Dose Adjustments
* **Renal Impairment:** No specific adjustment required for lower GFR, but higher doses may be needed for diuretic resistance. Monitor closely for acute kidney injury.
* **Hepatic Impairment:** Start at the lower end of the dosing range to prevent electrolyte imbalances and hepatorenal syndrome.
## Contraindications
* Anuria.
* Hypersensitivity to furosemide or sulfonamides (though cross-reactivity is clinically debated).
* Severe hepatic coma or electrolyte depletion.
## Adverse Effects
* **Common:** Hypokalemia, hyponatremia, hypomagnesemia, hypocalcemia, dehydration, and hypotension.
* **Serious:** Ototoxicity (transient or permanent, typically dose-related), hyperglycemia, hyperuricemia (gout), and interstitial nephritis.
## Key Drug Interactions
* **Aminoglycosides:** Increased risk of ototoxicity and nephrotoxicity.
* **Lithium:** Furosemide reduces lithium clearance, increasing the risk of toxicity.
* **NSAIDs:** May blunt the diuretic and antihypertensive effect of furosemide; increased risk of renal impairment.
* **ACE Inhibitors/ARBs:** Increased risk of severe hypotension and renal insufficiency, especially when started concurrently.
## Monitoring
* **Labs:** Serum electrolytes (potassium, sodium, magnesium, calcium), BUN, creatinine, and uric acid.
* **Clinical:** Blood pressure, daily body weight, fluid intake/output, and signs of clinical dehydration or edema resolution.
* **Hearing:** Assess for tinnitus or hearing loss, particularly with high-dose regimens.
## Clinical Pearls
* **Timing:** Administer early in the day to prevent nocturia.
* **Diuretic Resistance:** In chronic heart failure, if efficacy wanes, consider changing to a split-dose regimen, adding a thiazide diuretic (e.g., metolazone) for synergistic effect, or ensuring optimal sodium restriction.
* **Bioavailability:** The oral bioavailability of furosemide is variable (10%–100%; average ~50%). Transitioning from IV to oral typically requires a 1:2 dose conversion as a conservative starting point.
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**Disclaimer:** This information is for educational purposes and does not replace professional clinical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors before administration.
