Loading Dose

Day	INR	Dose of Warfarin
1		5mg
2		5mg
3		5mg
4	<1.2 1.3 1.4 1.5 1.6 1.7 – 1.8 1.9 – 2.0 2.1 – 2.2 >2.3	8mg 7mg 6mg 5mg 4mg 3mg 2mg 1mg nil
6+	If INR therapeutic use day 4 dose as maintenance dose otherwise increase the dose 1mg if sub-therapeutic or reduce the dose by 1mg if the dose is above the range by <0.3 If the INR is >3.3 miss at least 1 day of treatment and reduce the dose.

Starting Warfarin

If the patient is stable with no significant co-morbidities it is reasonable to give 3 days of treatment before checking the INR. A loading dose of 5mg is safe in most cases. In an older or frail patient starting with 3mg daily is an acceptable alternative. The suggestions on day 4 outlined above can be used for a loading dose of 5mg or 3mg. This is a relatively gentle approach to starting warfarin. It would be unusual for this to lead to a high INR result. Repeat the INR on day 6. If the INR is therapeutic continue with the same maintenance dose, otherwise make minor adjustments depending on the INR. If the day 6 INR is >3.3, be cautious and miss at least 1 day. Be aware that during loading the INR could continue to rise if treatment is not interrupted.

If there are any concerns it is important to discuss with the patient’s own doctor.