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# Furosemide (Lasix)
## Overview
Furosemide is a potent loop diuretic that inhibits the reabsorption of sodium, chloride, and potassium in the ascending limb of the Loop of Henle. This leads to increased excretion of water, sodium, chloride, potassium, calcium, and magnesium.
## Primary Indications
* Edema associated with heart failure, liver cirrhosis, and renal disease (including nephrotic syndrome).
* Hypertension (often in combination with other antihypertensives).
* Management of ascites.
## Adult Dosing
* **Edema:** Initial dose typically 20-80 mg PO once or twice daily. May increase by 20-40 mg every 6-8 hours until desired response is achieved. Usual maintenance dose is 40-80 mg PO once daily. Maximum single dose is 80 mg PO; however, higher doses may be used under strict medical supervision, especially in hospitalized patients.
* **Hypertension:** Initial dose typically 40 mg PO twice daily. May be adjusted based on response.
* **Intravenous (IV) dosing:** Equivalent to oral doses, but onset is more rapid. Initial dose typically 20-40 mg IV once. Subsequent doses may be 20-80 mg IV. Higher doses may be required in severe renal impairment.
## Pediatric Dosing
* **Edema:** 1-2 mg/kg/dose PO every 6-12 hours. Maximum dose 6 mg/kg/day.
* **IV Dosing:** 1 mg/kg/dose IV every 6-12 hours. Maximum dose 6 mg/kg/day.
* *Note: Dosing in neonates and premature infants can be highly variable and requires careful monitoring.*
## Dose Adjustments
* **Renal Impairment:** Dose may need to be increased in patients with severe renal impairment due to reduced protein binding and impaired tubular secretion. However, excessive doses can lead to ototoxicity.
* **Hepatic Impairment:** Dose adjustments may be necessary; close monitoring of electrolytes and fluid status is crucial.
## Contraindications
* Anuria.
* Known hypersensitivity to furosemide or sulfonamides (cross-sensitivity may occur).
* Severe electrolyte depletion (e.g., hypokalemia, hyponatremia).
## Adverse Effects
* **Common:** Dizziness, lightheadedness, orthostatic hypotension, weakness, headache, nausea, diarrhea.
* **Electrolyte Disturbances:** Hypokalemia, hyponatremia, hypochloremia, hypomagnesemia, hypocalcemia.
* **Metabolic:** Hyperglycemia, hyperuricemia (can precipitate gout).
* **Ototoxicity:** Hearing impairment, tinnitus (especially with rapid IV administration or high doses).
* **Renal:** Increased BUN and creatinine.
* **Hematologic:** Agranulocytosis, thrombocytopenia, aplastic anemia (rare).
* **Dermatologic:** Rash, photosensitivity.
## Key Drug Interactions
* **Aminoglycosides and other ototoxic drugs:** Increased risk of ototoxicity.
* **Antihypertensives (including ACE inhibitors, ARBs, beta-blockers):** Additive hypotensive effect.
* **Digoxin:** Increased risk of digoxin toxicity due to furosemide-induced hypokalemia.
* **Lithium:** Decreased renal clearance of lithium, increasing risk of lithium toxicity.
* **NSAIDs:** May reduce the diuretic and antihypertensive effects of furosemide.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** May be used to counteract potassium loss.
* **Thiazide diuretics:** Additive diuretic effect and electrolyte depletion.
## Monitoring
* **Electrolytes:** Serum electrolytes (sodium, potassium, chloride, magnesium, calcium), especially with initiation or dose changes, and in patients with risk factors.
* **Renal Function:** Serum creatinine and BUN.
* **Fluid Balance:** Daily weights, intake and output.
* **Blood Pressure:** Monitor for hypotension, especially with concomitant antihypertensives.
* **Hearing:** Assess for tinnitus or hearing loss.
## Clinical Pearls
* Furosemide is a potent diuretic; titrate doses carefully to avoid excessive diuresis, dehydration, and electrolyte imbalances.
* Administer IV furosemide slowly (e.g., over 1-2 minutes) to minimize the risk of ototoxicity. For doses >80 mg, continuous IV infusion may be preferred.
* Concurrent administration of potassium supplements or potassium-sparing diuretics may be necessary to prevent or manage hypokalemia.
* Monitor patients closely for signs of dehydration, electrolyte abnormalities, and hypotension.
* In patients with severe edema due to heart failure, consider initiating therapy with continuous IV infusion.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant literature before making clinical decisions. Dosing and management may vary based on individual patient factors and local protocols.*
