What is the equivalent intravenous (IV) dose of Lasix (furosemide) when switching from oral (PO) in patients with heart failure?

PO to IV Furosemide Conversion in Heart Failure

When switching from oral to IV furosemide in heart failure patients, use an initial IV dose that is at least equivalent to (1:1 ratio) or higher than the oral dose, as oral bioavailability is reduced in decompensated heart failure. 1

Conversion Ratio and Initial Dosing

The standard conversion is 1:1 (oral dose = IV dose) as the minimum starting point. 1 The European Society of Cardiology specifically recommends that for patients experiencing heart failure exacerbation, the initial IV dose should be "at least equivalent to the oral dose." 1

Specific Dosing Guidelines:

• For patients already on chronic oral furosemide: Start IV furosemide at a dose equal to or greater than their home oral dose 1
• For diuretic-naïve patients with acute heart failure: Start with 20-40 mg IV 1, 2
• For acute pulmonary edema: Initial dose is 40 mg IV, which can be increased to 80 mg IV if inadequate response within 1 hour 2

Rationale for 1:1 or Higher Conversion

The 1:1 conversion accounts for the fact that:

• IV administration provides faster onset and more reliable absorption compared to oral during acute decompensation 1
• Oral bioavailability is significantly reduced in decompensated heart failure due to gut edema and reduced absorption 1
• IV furosemide bypasses first-pass metabolism and achieves more predictable drug delivery to the nephron 3

Administration Method

You have two options for IV delivery, with continuous infusion showing superior efficacy:

• Continuous infusion is more effective than bolus injection for the same total daily dose, producing higher urinary volume (2,860 vs 2,260 mL) and sodium excretion (210 vs 150 mmol) 3
• Continuous infusion causes less ototoxicity (no hearing loss vs 25% with bolus) 3
• Bolus administration: Give slowly over 1-2 minutes, can repeat every 2 hours if needed 2
• Continuous infusion protocol: Give 20% of total dose as loading bolus, then infuse remainder over 8-24 hours at rate not exceeding 4 mg/min 2, 3

Dose Escalation Strategy

If initial IV dose is inadequate:

• Increase by 20 mg increments every 2 hours until desired diuretic effect is achieved 1, 2
• Maximum daily dose can reach 600 mg (and occasionally higher in severe cases) 4, 5
• Target weight loss of 0.5-1.0 kg daily during active diuresis 4, 1

Critical Monitoring Requirements

• Track urine output continuously to assess diuretic response 1
• Monitor renal function and electrolytes (especially potassium) frequently 1, 6
• Check daily weights to guide dose adjustments 4, 6
• Watch for hypotension and azotemia - if these occur, slow but don't stop diuresis until fluid retention is eliminated 1, 6

Essential Concurrent Therapy

Never use diuretics in isolation - this is a critical pitfall:

• Continue ACE inhibitors/ARBs during IV diuretic therapy unless patient is hemodynamically unstable (SBP <90 mmHg), as they work synergistically with diuretics 1
• Continue beta-blockers during exacerbation unless hemodynamically unstable 1
• Inappropriate diuretic dosing undermines the efficacy of other heart failure medications 4, 6

Common Pitfalls to Avoid

• Underdosing due to excessive concern about hypotension/azotemia leads to refractory edema 1, 6
• Using less than the oral dose when converting to IV results in inadequate diuresis 1
• Stopping guideline-directed medical therapy (ACE inhibitors, beta-blockers) during diuretic escalation unless truly hemodynamically unstable 1
• Failing to adjust pH of infusion solution above 5.5 when using continuous infusion, which causes drug precipitation 2