Dose Adjustments

Always take into account potential reasons for elevated and subtherapeutic INRs—there is a need to evaluate more than just the number. Ask your patient about “the 4 Ds” that can influence warfarin dose requirements:

  1. Diet—any major changes (fasting, weight watchers), liver or mango consumption?
  2. Drugs—any new medicines, discontinued medicines since last INR check?
  3. Dose—confirm current warfarin dose, any missed doses?
  4. Disease—any recent illness, fever, N/V/D?

A nice "rule of thumb" for dose adjustments near the target range (generally works for INRs from the high 1s to low 4s): If you want to change the INR by 0.5-1 unit, increase or decrease the weekly dose by a daily dose.

Example: Your patient has been taking warfarin 5mg daily for >2 weeks and INR is 1.8. Adding 5mg to the week (for instance, 5mg Monday-Friday with 7.5mg Saturday-Sunday) should increase the INR into the mid-2s.