Loop diuretic

Background

• Mechanism: Inhibits Na-K-2Cl carrier in the thick ascending Loop of Henle^1^
• Potency: Highest among diuretic classes
• Adverse Effects
  • Hypokalemia (most common)
  • Hypomagnesemia, hyponatremia, hypocalcemia
  • Ototoxicity (associated with rapid IV push)
  • Pre-renal AKI (due to over-diuresis)
• Sulfa Allergy: Most are sulfonamide derivatives; cross-reactivity is rare but possible

Key Agents

• Furosemide (Lasix)
  • Bioavailability: Highly variable PO absorption (10-90%, avg ~50%)
    • IV dose is approx 2x as potent as PO dose (e.g., 20mg IV ≈ 40mg PO)
  • Dosing: In CHF, usually start with 1-2.5x the patient's daily home dose IV

• Bumetanide (Bumex)
  • Potency: ~40x more potent than furosemide
    • 1 mg Bumetanide ≈ 40 mg Furosemide
  • Bioavailability: High and reliable absorption (>80%)
  • Often reserved for patients refractory to furosemide or with severe gut edema

• Torsemide (Demadex)
  • Kinetics: Longer half-life than furosemide
  • Bioavailability: Excellent oral absorption
    • PO dose is essentially equivalent to IV dose
  • Less common in acute resuscitation; helpful for chronic management

• Ethacrynic acid (Edecrin)
  • Class: Phenoxyacetic acid derivative (not a sulfonamide)
  • Indication: The only alternative for patients with severe or anaphylactic sulfa allergy
  • Toxicity: Highest risk of ototoxicity among loop diuretics
  • Seldom used as first-line due to side effect profile

See Also

• CHF
• Pulmonary Edema
• Diuretics