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INR = (Prothrombin Time (PT) / Average Normal PT) ISI
Related Formula: IWPC Warfarin Dosage Calculation Formula
Consensus on Warfarin Anticoagulation Therapy in China: Recommendations for Warfarin Anticoagulation Therapy
To reduce the risk of excessive anticoagulation, loading doses are generally not recommended. For non-urgent treatments (such as chronic atrial fibrillation) in outpatient settings, due to the inconvenience of external monitoring, loading doses are also not recommended for safety.
It is suggested that the initial dose for Chinese individuals be 1–3 mg (the main dosage forms of warfarin in China are 2.5 mg and 3 mg), which can reach the target range in 2–4 weeks.
For certain patients, such as the elderly, those with liver dysfunction, congestive heart failure, and high bleeding risk patients, the initial dose may be appropriately reduced.
If the INR results are continuously measured to be outside the target range, dose adjustment should start after identifying the reason without rushing to change the dose.
For small dose adjustments of warfarin, weekly dosing calculations can be more precise than adjusting daily doses.
If the INR exceeds the target range, the original dose can be increased or decreased by 5%-20%, and monitoring should be strengthened after dose adjustment.
If the INR remains stable, with occasional fluctuations not exceeding 0.5 above or below the target range, dose adjustment is not necessary; INR can be rechecked as appropriate (within days or 1-2 weeks).
| INR Abnormal Increase or Bleeding Conditions | Measures to be Taken |
|---|---|
| INR >3.0–4.5 (no bleeding complications) | Appropriately reduce the warfarin dose (5%–20%) or skip one dose, and recheck INR after 1-2 days. Adjust the warfarin dose when INR returns to the target value and restart treatment, or enhance monitoring to see if INR can return to therapeutic levels while identifying factors that may have caused the INR increase. |
| INR >4.5–<10.0 (no bleeding complications) | Stop warfarin, administer intramuscular vitamin K (1.0–2.5 mg), and recheck INR after 6–12 hours. Restart treatment with a small dose of warfarin when INR <3. |
| INR ≥10.0 (no bleeding complications) | Stop warfarin, administer intramuscular vitamin K (5 mg), and recheck INR after 6–12 hours. Restart treatment with a small dose of warfarin when INR <3. If the patient has high bleeding risk factors, consider administering fresh frozen plasma, prothrombin complex concentrate, or recombinant factor VIIa. |
| Severe bleeding (regardless of INR level) | Stop warfarin. Administer intramuscular vitamin K (5 mg). Administer fresh frozen plasma, prothrombin concentrate, or recombinant factor VIIa. Continuously monitor INR. After stabilizing the condition, re-evaluate the necessity of warfarin treatment. |