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# Furosemide (Lasix)
## Overview
Furosemide is a potent loop diuretic that inhibits the reabsorption of sodium and chloride in the ascending limb of the loop of Henle, leading to increased excretion of water, sodium, chloride, potassium, and hydrogen ions.
## Primary Indications
* Edema associated with congestive heart failure (CHF)
* Edema associated with hepatic cirrhosis
* Edema associated with renal disease, including nephrotic syndrome
* Hypertension (less commonly used as first-line)
* Ascites
## Adult Dosing
* **Edema:**
* **Oral:** 20 mg to 80 mg once daily, then increased as needed. Doses may be given every day, every other day, or for 3-4 days a week. Doses above 80 mg/day are usually not more effective and may increase adverse effects.
* **Intravenous (IV) or Intramuscular (IM):** 20 mg to 40 mg once daily. If no response, increase by 20 mg every 2 hours until an adequate response is obtained.
* **Hypertension:**
* **Oral:** 40 mg twice daily. This indication is generally not preferred due to its short duration of action and potential for electrolyte imbalances.
* **Acute Pulmonary Edema:**
* **IV:** 40 mg administered slowly over 30-40 minutes. If response is inadequate, another 40 mg IV may be given after 2 hours.
## Pediatric Dosing
* **Edema:**
* **Oral:** 1 mg/kg to 2 mg/kg once daily, not to exceed 6 mg/kg/day. Doses can be given once or twice daily.
* **IV or IM:** 1 mg/kg once daily, not to exceed 6 mg/kg/day. If ineffective, doses can be increased by 1 mg/kg every 2 hours.
## Dose Adjustments
* **Renal Impairment:** Doses may need to be increased in patients with renal impairment due to decreased drug elimination. Careful monitoring of response and electrolytes is crucial. In patients with significant renal impairment, continuous IV infusion may be more effective than bolus doses.
* **Hepatic Impairment:** May require dose reduction due to altered metabolism and protein binding.
## Contraindications
* Anuria
* History of hypersensitivity to furosemide or sulfonamides (cross-sensitivity may occur)
* Severe electrolyte depletion (e.g., hypokalemia, hyponatremia)
## Adverse Effects
* **Electrolyte imbalances:** Hypokalemia, hyponatremia, hypochloremia, hypomagnesemia, hypocalcemia, hyperuricemia (can precipitate gout)
* **Dehydration:** Especially in the elderly or with aggressive diuresis
* **Ototoxicity:** Particularly with rapid IV administration or in patients with impaired renal function/high doses. Usually reversible.
* **Hypotension**
* **Hyperglycemia**
* **Aplastic anemia, agranulocytosis, thrombocytopenia** (rare)
* **Dizziness, lightheadedness, headache**
* **Rash, photosensitivity**
## Key Drug Interactions
* **Aminoglycosides and other ototoxic drugs:** Increased risk of ototoxicity.
* **ACE inhibitors and ARBs:** Increased risk of hypotension and renal dysfunction, especially in volume-depleted patients.
* **Corticosteroids:** Increased risk of hypokalemia.
* **Digoxin:** Increased risk of digoxin toxicity due to furosemide-induced hypokalemia and enhanced renal clearance of digoxin.
* **Lithium:** Reduced renal clearance of lithium, leading to increased serum lithium levels and risk of toxicity.
* **NSAIDs:** May decrease furosemide's diuretic and antihypertensive effect.
* **Potassium supplements or potassium-sparing diuretics:** May counteract hypokalemia, but careful monitoring is still needed.
## Monitoring
* **Electrolytes:** Serum electrolytes (sodium, potassium, chloride, magnesium, calcium) frequently, especially during initiation and dose changes.
* **Renal function:** Serum creatinine and BUN.
* **Fluid balance:** Daily weights, intake and output.
* **Blood pressure:** Especially in patients with hypertension or those at risk of hypotension.
* **Blood glucose:** In diabetic patients.
* **Uric acid:** In patients with a history of gout.
* **Auditory function:** If ototoxicity is suspected.
## Clinical Pearls
* Administer oral furosemide in the morning to minimize nocturia.
* IV furosemide administration should be slow (e.g., over 30-60 minutes) to reduce the risk of ototoxicity and hypotension, unless in acute emergencies where faster administration may be considered under close monitoring.
* Rapid IV administration of furosemide can cause transient hearing impairment and tinnitus.
* Furosemide is highly protein-bound; in hypoalbuminemic states, a higher proportion of unbound, active drug is available, potentially requiring dose adjustments.
* For patients who do not respond adequately to oral furosemide, consider switching to IV administration or increasing the dose. Continuous infusion may be more effective than intermittent boluses in some refractory cases.
* Monitor for signs of dehydration, such as dry mucous membranes, decreased skin turgor, and oliguria.
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*Disclaimer: This information is for educational purposes only and does not substitute for professional medical advice. Always consult with a qualified healthcare provider to determine the best course of treatment for your specific condition and to ensure you have the most up-to-date information. Verify current prescribing information with the manufacturer's package insert.*
