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

Oral vitamin K1 is used for the treatment of excessive anticoagulation. Detailed information on changes in the International Normalized Ratio (INR) in response to vitamin K1 is not available. We therefore measured the INR for the first 7 d following the oral intake of 1-5 mg of vitamin K1 in 24 patients routinely treated with phenprocoumon who had an INR > or =6.0 at presentation. On the first 2 d after administration of vitamin K1, 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 K1 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 > or =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.