furosemide

the loop

A loop diuretic acting on the thick ascending limb of the Loop of Henle. The cornerstone of volume management in heart failure, renal failure, and cirrhosis.

• Mechanism: Inhibits $N{a}^{+}-K^{+}-2C{l}^{-}$ cotransporter (NKCC2). Abolishes the medullary gradient (preventing urine concentration).
• Dosing:
  • Oral: Bioavailability ~50% (highly variable 10-100%).
  • IV: Potency is roughly 2x Oral Dose (e.g., 40 mg IV $\approx$ 80 mg PO).
  • Renal Failure: Requires higher doses to secrete drug into tubule.

indications

• Volume Overload: Heart Failure, Cirrhosis, Nephrotic Syndrome.
• Hypercalcaemia: Increases calcium excretion (after volume repletion).
• Hyperkalaemia: Kaliuresis.

adverse effects

• Electrolytes: Hypokalaemia, Hypomagnesemia, Hyponatremia.
• Hypovolemia/AKI: Prerenal azotemia.
• Ototoxicity: At very high doses/rapid infusion (usually > 240 mg/hr).
• Sulfa Allergy: Technically a sulfa drug, but cross-reactivity is minimal/theoretical. Safe in non-anaphylactic sulfa allergy.