Course of the International Normalized Ratio in response to oral vitamin K₁ in patients overanticoagulated with phenprocoumon

Oral vitamin K 1 is used for the treatment of excessive anticoagulation. Detailed information on changes in the International Normalized Ratio (INR) in response to vitamin K 1 is not available. We therefore measured the INR for the first 7 d following the oral intake of 1–5 mg of vitamin K 1 in 24 patients routinely treated with phenprocoumon who had an INR 6.0 at presentation. On the first 2 d after administration of vitamin K 1 , the mean INR decreased by 40% and 23% respectively. After day 2, the day‐to‐day proportional change in the mean INR depended on the dose of vitamin K 1 and varied from a decrease of 12% to an increase of 21%. On day 7 the mean INR was higher than on day 2 in three out of five treatment groups. Between day 2 and day 7, in general, 32% of the patients had an INR value within the target zone, 25% had an INR value 6.0 and 8% had an INR value <2.0. These findings suggest that our routine treatment of overanticoagulation in patients on phenprocoumon should be intensified to improve its efficacy.