Step 1: The patient is started on an oral anticoagulant regimen designed to achieve a target INR.
Step 2: Determine the current INR and compare to the target value.
Step 3: If the current INR is either too high or too low, then separate protocols are employed to handle the patient (neither specified in the paper).
(3a) If the INR is too low, this may include review of patient compliance and looking for dietary, drug or other cause of interference.
(3b) If the INR is too high, the response may range from simply holding 1-2 doses to reversal with low dose vitamin K to administration of FFP.
(3c) The values for too high or too low can varied by the user. According to Britt et al (page 1003), undertreatment could be set as an INR 0.5 to 1.0 below the target INR and overtreatment as 1.0 to 1.5 above the target INR. I will use 1.5 as the low end and 4.5 at the high end.
Step 4: If the observed INR is within a certain tolerance (percentage deviation) from the target INR, then no change in dosage is made.
Step 5: If the current INR is within the adjustment range and outside of the tolerance limits, then the dose is adjusted using the following equation:
dose of oral anticoagulant in mg =
= (old dose in mg) * (1 + ((dose adjustment coefficient) * LN ((target INR) / (observed INR))))
The dose adjustment coefficient (DAC) is a decimal fraction from 0 to 1.
(1) The original DAC was set at 0.66 but was lowered to 0.58.
(2) The DAC should not be below 0.5.
(3) The highest DAC reported was 0.77.
