A patient with decompensated heart failure and marked gut wall edema shows poor response to oral furosemide despite dose escalation. Which pharmacokinetic property makes switching to an alternative loop diuretic logical?

• A Ethacrynic acid has a longer duration of action than furosemide
• B Bumetanide undergoes less renal secretion so it reaches higher tubular levels
• C Torsemide has consistently high oral bioavailability even in edematous states ✓
• D Torsemide is excreted almost entirely unchanged in urine

Explanation

Oral furosemide bioavailability varies widely, roughly 10 to 100 percent between individuals, and falls further when intestinal mucosal edema delays absorption, explaining erratic response in decompensated heart failure. Torsemide has about 80 to 100 percent bioavailability regardless of gut edema and a longer half-life, making it a rational switch before resorting to intravenous therapy. Bumetanide shares furosemide's variability, and torsemide is substantially hepatically metabolized.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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