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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.
## Primary Indications
* Edema associated with congestive heart failure.
* Edema associated with hepatic cirrhosis or renal impairment (including nephrotic syndrome).
* Hypertension (adjunctive therapy).
## Adult Dosing
* **Edema:** Initial dose 20–80 mg orally once daily. If response is insufficient, increase by 20–40 mg at intervals of 6–8 hours until desired effect is reached. Maximum single dose typically 600 mg (rare, clinical judgment required).
* **Hypertension:** 20–40 mg orally twice daily.
## Pediatric Dosing
* **Edema:** Initial dose 2 mg/kg/dose once daily. Increase by 1–2 mg/kg/dose no more frequently than every 6–8 hours as needed.
* **Maximum Dose:** 6 mg/kg/dose.
## Dose Adjustments
* **Renal Impairment:** No specific adjustment required, but higher doses may be necessary in patients with severe chronic kidney disease.
* **Hepatic Impairment:** Use cautiously; rapid alterations in fluid/electrolyte balance may precipitate hepatic encephalopathy. Dose titration should be conservative.
## Contraindications
* Anuria.
* Hypersensitivity to furosemide or sulfonamides (though cross-reactivity is clinically debated).
* Severe electrolyte depletion (hypovolemia, hyponatremia, hypokalemia).
## Adverse Effects
* **Common:** Polyuria, dizziness, orthostatic hypotension.
* **Serious:** Hypokalemia, hypomagnesemia, hyponatremia, dehydration, hyperuricemia (gout risk), and ototoxicity (usually dose-related and associated with rapid IV administration).
## Key Drug Interactions
* **Ototoxic drugs (e.g., Aminoglycosides):** Increased risk of hearing loss/tinnitus.
* **NSAIDs:** May attenuate the diuretic/natriuretic effect of furosemide and increase the risk of acute kidney injury.
* **Lithium:** Furosemide may cause increased lithium levels (reduced clearance/toxicity).
* **ACE Inhibitors/ARBs:** Increased risk of hypotension and acute kidney injury, especially when initiating therapy or increasing doses.
## Monitoring
* **Electrolytes:** Potassium, magnesium, sodium, and chloride.
* **Renal Function:** Serum creatinine and BUN.
* **Volume Status:** Daily weights, blood pressure, and intake/output monitoring.
* **Hearing:** Assess for tinnitus or hearing changes with high-dose therapy.
## Clinical Pearls
* **Diuretic Resistance:** If response is inadequate, consider conversion to a continuous infusion or the addition of a thiazide diuretic (sequential nephron blockade, e.g., metolazone) for synergistic effect.
* **Timing:** Administer in the morning to prevent nocturia.
* **Bioavailability:** Oral bioavailability is ~50–60%; transition from IV to oral often requires doubling the dose.
* **Uncertainty Note:** Specific titration protocols vary by institution; always consult local institutional guidelines for chronic heart failure management or pediatric acute care protocols.
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**Disclaimer:** This information is for educational purposes only. Clinical practice varies based on patient-specific factors and institutional protocols. Always verify current prescribing information, contraindications, and drug interactions via a reliable clinical database (e.g., Lexicomp, UpToDate) before prescribing or administering medication.
