acetazolamide

2 min read Updated 2026-03-15
cardiology nephrology pharmacology diuretics
Contents
acetazolamide

Carbonic anhydrase inhibitor at the proximal tubule. Used upfront to prevent diuretic resistance in ADHF — not as a rescue agent. The key: it is chloride-sparing, maintaining macula densa Cl⁻ delivery and suppressing neurohormonal activation. ADVOR (2022): NNT ≈ 9 for decongestion; no mortality benefit.

mechanism

Inhibits carbonic anhydrase (types II/IV) in the proximal tubule → blocks NaHCO₃ reabsorption → bicarbonaturic diuresis. Spares chloride (unlike loops/thiazides which waste it). More Cl⁻ to macula densa → suppresses renin → prevents neurohormonal brake on natriuresis.

dosing

RouteDoseFrequencyNotes
IV (preferred)500 mgOnce dailyGive upfront from day 1
PO500 mgOnce dailyReasonable bioavailability (~100%)
Severe gut oedema500–1000 mgBID
  • Tolerance develops in ~48h — plan to stop or rotate after 2–3 days
  • Alternate-day dosing for prolonged courses

key points

prevention, not rescue

ADVOR gave acetazolamide upfront to all patients from day 1. It prevents diuretic resistance by preserving chloride. Once distal tubular hypertrophy has developed (days of loop monotherapy), thiazides are more appropriate.

  • Best response when baseline HCO₃⁻ ≥ 27 mmol/L (metabolic alkalosis = substrate)
  • Less effective if home furosemide > 60 mg/day (ADVOR subanalysis) — distal hypertrophy already established
  • ADVOR excluded SGLT2i patients — synergy extrapolated, not proven
  • ADVOR patients received daily Mg²⁺ infusions — replicate this
  • AKI signal: Cr rise > 26 µmol/L in 40% vs. 20% — monitor closely
contraindications
  • Respiratory compromise (non-intubated) — reduces metabolic compensation for respiratory acidosis
  • Hypernatraemia — increases free water excretion; allow liberal drinking
  • Advanced liver disease — encephalopathy risk
  • GFR < 10 mL/min

adverse effects

  • Metabolic acidosis (expected; self-limiting — this is why tolerance develops)
  • Paraesthesias (very common; benign)
  • Hypokalaemia
  • AKI (ADVOR signal — 40% vs. 20%)
  • Nephrolithiasis (chronic use only; not relevant to short-course ADHF)

evidence

  • ADVOR (2022) — n=519; acetazolamide + loop vs. loop alone: decongestion 42% vs. 31% (NNT ≈ 9); no 3-month mortality difference; chloride preserved in treatment arm

Key references