====== Furosemide (Lasix®) ======

<WRAP right 340px>
<WRAP infobox>
^ Furosemide | {{ :cardio:diuretics:furosemide.svg?200 |}} |
| Brand Name | Lasix® |
| Drug Class | [[cardio:diuretics:start|Loop Diuretic]] |
| Primary Indication | Edema, Heart Failure |
| Site of Action | Thick Ascending Limb |
| Mechanism | Na⁺/K⁺/2Cl⁻ Cotransporter Inhibition |
| Potassium Effect | ↓ (Hypokalemia risk) |
| Calcium Effect | ↓ Reabsorption |
| Bioavailability | Variable (~50%) |
| Half-Life | ~1–2 hours |
| FDA Approval | 1966 |
</WRAP>
</WRAP>

===== Overview =====

Furosemide is a loop diuretic that inhibits sodium reabsorption in the thick ascending limb of the loop of Henle.

It is a potent natriuretic agent used primarily for volume overload states including heart failure, cirrhosis, and renal disease.

Loop diuretics remain the cornerstone of acute decompensated heart failure management.

<WRAP clear></WRAP>

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===== Mechanism of Action =====

**Site of Action**
  * Thick ascending limb of the loop of Henle  

**Transporter Blocked**
  * Na⁺/K⁺/2Cl⁻ cotransporter (NKCC2)  

**Physiologic Effects**
  * ↑ Sodium and water excretion  
  * ↑ Potassium excretion  
  * ↑ Calcium excretion  
  * ↑ Magnesium excretion  
  * Disrupts medullary concentration gradient  

Net effect:
  * Powerful diuresis  
  * Rapid reduction in preload  

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===== Indications =====

  * Acute decompensated heart failure  
  * Chronic heart failure  
  * Pulmonary edema  
  * Cirrhosis with ascites  
  * Nephrotic syndrome  
  * Severe hypertension (adjunct)  
  * Hypercalcemia (with IV fluids)  

Effective even when eGFR < 30.

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<WRAP contra>
===== Contraindications =====

Absolute:
  * Anuria  
  * Severe electrolyte depletion  

Relative / Caution:
  * Hypotension  
  * Dehydration  
  * Gout  
  * Concomitant nephrotoxic drugs  

</WRAP>

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<WRAP details>
===== Dosing =====

Oral:
  * 20–80 mg once or twice daily  

IV (acute HF):
  * 20–40 mg initial dose  
  * Titrate based on response  

Higher doses required in renal impairment.

Dose-response curve is steep.

</WRAP>

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<WRAP details>
===== Pharmacokinetics =====

Absorption:
  * Oral and IV  

Bioavailability:
  * ~50% (variable)  

Half-life:
  * ~1–2 hours  

Duration:
  * 6–8 hours  

Elimination:
  * Renal  

Short duration often requires twice-daily dosing.

</WRAP>

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<WRAP details>
===== Adverse Effects =====

Electrolyte:
  * Hypokalemia  
  * Hyponatremia  
  * Hypomagnesemia  
  * Hypocalcemia  

Metabolic:
  * Hyperuricemia  
  * Metabolic alkalosis  

Other:
  * Ototoxicity (high doses or rapid IV infusion)  
  * Hypotension  
  * Volume depletion  

</WRAP>

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<WRAP details>
===== Drug Interactions =====

Aminoglycosides:
  * ↑ Ototoxicity risk  

Lithium:
  * ↑ Lithium levels  

RAAS inhibitors:
  * Additive hypotension  

Other diuretics:
  * Additive electrolyte abnormalities  

</WRAP>

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<WRAP monitoring>
===== Monitoring =====

  * Weight  
  * Urine output  
  * Electrolytes (Na⁺, K⁺, Mg²⁺)  
  * Renal function  
  * Blood pressure  

</WRAP>

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<WRAP pearls>
===== Clinical Pearls =====

  * Most commonly used loop diuretic.  
  * Effective in renal impairment.  
  * Causes hypokalemia and metabolic alkalosis.  
  * IV administration acts within minutes.  
  * Ototoxicity risk with high-dose or rapid infusion.  
  * Often combined with thiazides for diuretic synergy.  

</WRAP>

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===== Comparison Within Class =====

Compared to [[cardio:diuretics:chlorthalidone|Chlorthalidone]]:
  * More potent  
  * Effective in renal failure  
  * Shorter duration  

Compared to [[cardio:diuretics:torsemide|Torsemide]]:
  * Shorter half-life  
  * More variable bioavailability  

Compared to [[cardio:diuretics:bumetanide|Bumetanide]]:
  * Less potent per mg  
  * More commonly used  

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===== Related =====

  * [[cardio:diuretics:start|Diuretics]]
  * [[cardio:heart_failure:start|Heart Failure]]
  * [[cardio:diuretics:chlorthalidone|Chlorthalidone]]
  * [[cardio:diuretics:spironolactone|Spironolactone]]