What is the equivalent oral dose of furosemide (Lasix) for a patient being discharged after receiving 80mg of intravenous (IV) furosemide?

Converting IV to Oral Furosemide at Discharge

When converting from 80mg IV furosemide to oral dosing at discharge, you should prescribe 160mg oral furosemide daily (typically given as 80mg twice daily), which represents a 2:1 oral-to-IV conversion ratio. 1

Conversion Rationale

The 2:1 conversion ratio accounts for the reduced bioavailability of oral furosemide compared to IV administration:

• Oral furosemide has approximately 50% bioavailability compared to IV administration, necessitating higher oral doses to achieve equivalent diuretic effect 1
• The American Journal of Kidney Diseases specifically recommends doubling the IV dose when converting to oral formulation to maintain the same total daily furosemide equivalent 1
• IV administration provides more rapid onset and predictable absorption, while oral administration may be affected by gut edema in heart failure states 1

Practical Dosing Strategy

For your patient on 80mg IV furosemide:

• Prescribe 160mg oral furosemide total daily dose, typically divided as 80mg twice daily (8 AM and 2 PM) 2
• The twice-daily schedule is preferred over once-daily dosing to maintain more consistent diuretic effect throughout the day 2
• In patients with severe CHF, once versus twice daily administration shows similar efficacy, but twice daily may provide better volume control 3

Critical Monitoring After Conversion

Watch for signs of inadequate conversion within 24-48 hours of discharge:

• Weight gain >2-3 lbs in 24-48 hours indicates under-diuresis 1
• Recurrent dyspnea or orthopnea suggests inadequate volume control 1
• Worsening peripheral edema signals need for dose adjustment 1
• Monitor electrolytes (sodium, potassium) within 3-7 days of discharge 4

When Higher Doses May Be Needed

Consider starting at 160mg twice daily (320mg total daily) if:

• The patient has advanced heart failure with chronic diuretic requirements >160mg/day 1
• There is evidence of diuretic resistance despite adequate IV dosing 1
• The patient has significant residual volume overload at discharge 4

The FDA label permits careful titration up to 600mg/day in patients with clinically severe edematous states, though doses exceeding 80mg/day require careful clinical observation and laboratory monitoring 2

Common Pitfall to Avoid

Do not simply prescribe 80mg oral furosemide (the same numeric dose as IV) - this represents only 50% of the effective diuretic dose and will result in volume reaccumulation and early readmission 1. The 2:1 conversion ratio is essential for maintaining adequate diuresis after discharge.

Alternative Strategy for Diuretic Resistance

If the patient shows inadequate response to 160mg oral twice daily:

• Add a thiazide diuretic (hydrochlorothiazide 25mg) or aldosterone antagonist (spironolactone 25-50mg) rather than escalating furosemide doses indefinitely 1
• Sequential nephron blockade is more effective than monotherapy escalation 4