Reversal of asymptomatic over-anticoagulation by orally administered vitamin K.

Over-anticoagulation with warfarin is common. There is good reason to reverse significantly high international normalised ratios (INRs), however, in practice, there is wide variation in the means to achieve this. Randomised controlled trials have provided evidence for using low dose orally administered phytomenadione for the reversal of asymptomatic over-anticoagulation. We devised an oral regimen using the intravenous preparation of phytomenadione (vitamin K1). Patients with an asymptomatic INR between 8.0 and 11.9 (n = 166) received 2.5 mg and those with an INR of 12.0-20.0 (n = 36) or >20 (n = 21) received 5 mg. Median INRs for the three groups of patients on day 1 (approximately 14 h) after vitamin K administration were 3.5, 3.0 and 2.9 respectively. In the patients given 2.5 mg, 77% had INRs between 2.0 and 4.9 on day 1. In the patients given 5 mg, 52% of those presenting with INRs of 12.0-20.0 returned between 2.0 and 4.9 1 d after administration of vitamin K. In the INR >20 group 44% returned with an INR between 2.0 and 4.9. Warfarin was reintroduced once the INR was <5 and the majority of patients remained stable for the following 14 d. This regimen for non-urgent correction is therefore effective and returns patients to a safe INR level without over-reversing anticoagulation.