Phenprocoumon (Falithrom) Dosing Guidelines
Phenprocoumon should be dosed once daily with the dose adjusted to maintain an INR of 2.0-3.0, typically starting at 0.08-0.15 mg/kg for adults. 1
Initial Dosing Recommendations
Adult Dosing:
- Initial dose: Once daily administration
- Typical starting dose ranges:
- Adults: 0.08-0.15 mg/kg once daily
- Elderly (>65 years): Consider starting at lower end of dosing range
Pediatric Dosing (if needed):
According to age-based recommendations 1:
- <1 year: 0.15 mg/kg once daily
1-5 years: 0.09 mg/kg once daily
- 6-10 years: 0.13 mg/kg once daily
- 11-18 years: 0.08 mg/kg once daily
Dose Adjustment Protocol
Dose adjustments should be made based on INR monitoring:
| INR Value | Dose Adjustment |
|---|---|
| 1.1-1.4 | Increase dose by 20% |
| 1.5-1.9 | Increase dose by 10% |
| 2.0-3.0 | No change (target range) |
| 3.1-3.5 | Decrease dose by 10% |
| >3.5 | Hold until INR <3.5, then restart at 20% lower dose |
| >10 | Hold medication and administer oral vitamin K |
Monitoring Schedule
- Initial phase: Check INR every 2-3 days until stable
- Maintenance phase: Monitor every 4-6 weeks once stable
- After dose changes: More frequent monitoring until stability is achieved
Important Clinical Considerations
Pharmacokinetic Properties
- Phenprocoumon has an extremely long half-life of 5.3-6.5 days (127-156 hours) 2, 3
- This long half-life can lead to:
- Slower achievement of steady-state
- Prolonged effect after discontinuation
- Potential for INR rebound phenomenon (seen in 27.6% of patients) 2
Special Populations
- Elderly patients (≥80 years) typically require lower doses
- Pregnant women: Phenprocoumon is contraindicated between weeks 6-12 of pregnancy due to teratogenic risk 1
- For pregnant women requiring anticoagulation, switch to LMWH with dose adjustment according to anti-Xa levels (target 0.8-1.2 U/mL 4-6 hours post-dose) 1
Bleeding Management
- For INR >10 without bleeding: Hold phenprocoumon and administer oral vitamin K
- For major bleeding: Reverse anticoagulation rapidly with IV vitamin K plus prothrombin complex concentrate
- Consider that phenprocoumon's long half-life may necessitate repeated vitamin K administration over several days 2
Common Pitfalls to Avoid
- Overdosing: Due to the long half-life, dose increases should be conservative (5-20% of weekly dose) to avoid cumulative effects
- Inadequate monitoring: Failure to monitor INR frequently enough during initiation or after dose changes
- Medication interactions: Many medications can potentiate or inhibit phenprocoumon's effect
- Dietary inconsistency: Fluctuations in vitamin K intake can affect INR stability
- Premature dose adjustment: Avoid adjusting dose based on a single out-of-range INR if the patient was previously stable
Phenprocoumon's extremely long half-life (5.3-6.5 days) makes it different from other vitamin K antagonists like warfarin (40 hours), requiring more cautious dosing approaches and longer monitoring periods after any dose adjustments 4.