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# Furosemide
## Overview
Furosemide is a potent loop diuretic used to reduce fluid overload in conditions such as heart failure, liver cirrhosis, and renal disease. It works by inhibiting 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 associated with congestive heart failure (CHF)
* Edema associated with liver cirrhosis
* Edema associated with renal disease, including the nephrotic syndrome
* Hypertension (as an adjunct therapy)
* Acute pulmonary edema
## Adult Dosing
* **Edema:** Oral: Initial dose 20-80 mg once daily. May increase by 20-40 mg every 6-8 hours as needed. Usual maintenance dose 40-80 mg once daily or divided BID. Maximum oral dose: 600 mg/day.
* IV/IM: Initial dose 20-40 mg once daily. May increase by 20 mg every 2 hours as needed. Usual maintenance dose 40-80 mg once daily or divided BID. Maximum IV/IM dose: 200 mg per dose.
* **Hypertension:** Oral: 40 mg BID.
* **Acute Pulmonary Edema:** IV: 20-40 mg, may repeat in 2 hours. If response is inadequate, further doses of 40 mg may be given.
*Note: Dosing for severe renal impairment or continuous infusion may differ and should be guided by local protocols and patient response.*
## Pediatric Dosing
* **Edema:** Oral: 1-2 mg/kg/dose once or twice daily. Maximum: 6 mg/kg/day.
* IV/IM: 1 mg/kg/dose once or twice daily. Maximum: 20 mg/dose.
* **Neonates:** Oral: 1 mg/kg/dose every 12-24 hours. IV/IM: 0.5-1 mg/kg/dose every 12-24 hours.
*Note: Dosing in neonates, especially premature infants, requires careful monitoring due to immature renal function.*
## Dose Adjustments
* **Renal Impairment:** Dose may need to be increased in patients with renal impairment due to reduced GFR and potential for decreased tubular secretion. However, excessive doses can lead to ototoxicity. Monitor response closely.
* **Hepatic Impairment:** Caution is advised. Electrolyte and fluid balance are critical.
## Contraindications
* Anuria
* Hypersensitivity to furosemide or sulfonamides (potential cross-sensitivity)
* Severe electrolyte depletion (e.g., hypokalemia, hyponatremia)
## Adverse Effects
* **Common:** Dizziness, lightheadedness, muscle cramps, weakness, dehydration, hypotension, orthostatic hypotension.
* **Electrolyte Imbalances:** Hypokalemia, hyponatremia, hypochloremia, hypomagnesemia, hypocalcemia.
* **Metabolic:** Hyperuricemia (gout), hyperglycemia, elevated cholesterol and triglycerides.
* **Ototoxicity:** Hearing loss (often reversible), tinnitus, especially with rapid IV administration or high doses.
* **Renal:** Increased BUN and creatinine.
* **Other:** Rash, photosensitivity, pruritus.
## Key Drug Interactions
* **Aminoglycosides:** Increased risk of ototoxicity and nephrotoxicity.
* **ACE Inhibitors/ARBs:** Increased risk of hypotension and renal dysfunction, particularly in volume-depleted patients.
* **NSAIDs:** May decrease natriuretic and antihypertensive effects; increased risk of renal dysfunction.
* **Digoxin:** Increased risk of digoxin toxicity due to furosemide-induced hypokalemia.
* **Lithium:** Reduced renal clearance of lithium, increasing risk of lithium toxicity.
* **Corticosteroids:** Additive hypokalemic effect.
* **Probenecid:** May decrease furosemide efficacy.
* **Warfarin:** May increase warfarin effect due to displacement from protein binding sites.
## Monitoring
* **Electrolytes:** Serum potassium, sodium, chloride, magnesium, and calcium.
* **Renal function:** Serum creatinine, BUN.
* **Fluid status:** Daily weights, intake/output.
* **Blood pressure:** Monitor for hypotension, especially with initiation or dose changes.
* **Hearing:** Assess for tinnitus or hearing impairment.
* **Glucose:** Monitor in diabetic patients.
## Clinical Pearls
* Oral administration may be delayed in onset but provides a longer duration of action compared to IV/IM.
* Rapid IV administration can increase the risk of ototoxicity. Administer IV infusions slowly.
* Monitor for signs of dehydration and electrolyte imbalances, especially in elderly patients or those with significant renal or hepatic impairment.
* If hypokalemia occurs, consider potassium supplementation or dietary modifications, but avoid in patients with significant renal impairment unless carefully managed.
* Concomitant use with other nephrotoxic agents should be avoided if possible.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for definitive guidance.*
