Digoxin PO to IV Conversion is NOT 1:1
No, digoxin conversion from oral (PO) to intravenous (IV) is not a 1:1 ratio due to differences in bioavailability. The FDA-approved digoxin label explicitly states that when switching from IV to oral formulations, you must account for bioavailability differences 1.
Conversion Ratios
According to the FDA drug label, the bioavailability differences require the following conversions 1:
Oral tablets (60-80% bioavailability):
- 62.5 mcg PO ≈ 50 mcg IV
- 125 mcg PO ≈ 100 mcg IV
- 250 mcg PO ≈ 200 mcg IV
- 500 mcg PO ≈ 400 mcg IV
This translates to approximately 0.8:1 ratio (IV:PO) - meaning you need about 80% of the oral dose when converting to IV.
Clinical Application
When converting from oral to IV:
- Multiply the oral dose by 0.8 to get the equivalent IV dose
- Example: A patient on 250 mcg PO daily would receive 200 mcg IV daily
When converting from IV to oral:
- Multiply the IV dose by 1.25 to get the equivalent oral dose
- Example: A patient on 200 mcg IV daily would receive 250 mcg PO daily
Important Caveats
Bioavailability varies by formulation:
- Standard tablets: 60-80% bioavailable
- Oral solution: Higher bioavailability (closer to 70-80%)
- Soft gelatin capsules: Even higher bioavailability (approaching 90-100%)
Research confirms these differences, with studies showing oral tablets provide approximately 75% bioavailability compared to IV administration 2, 3. One study specifically demonstrated that 0.5 mg oral tablet has similar bioavailability to 0.35-0.4 mg IV 2.
Monitor serum digoxin concentrations after any route conversion, as individual patient factors (renal function, drug interactions, body weight) significantly affect levels 1. Target therapeutic range is 0.5-1.0 ng/mL for most indications, with levels >1.2 ng/mL associated with increased mortality 4, 5.