The association of vitamin K status with warfarin sensitivity at the onsetof treatment

We investigated the association of vitamin K status with warfarin sensitivi ty among 40 orthopaedic patients beginning perioperative algorithm-dosed wa rfarin. [Baseline vitamin K status was assessed using plasma vitamin K-1 an d vitamin K-1 2.3 epoxide concentrations, and a questionnaire-based estimat ion of usual vitamin K intake. Warfarin sensitivity was assessed as the inc rease in the International Normalized Ratio (INR) after two doses of 5 mg o f warfarin and as the 4-d accumulation of under-gamma -carboxylated prothro mbin (PIVKA-II). adjusted for warfarin dose requirement. Multivariate model s were used to assess vitamin K variables as predictors of warfarin sensiti vity The mean INR increase was 0.53 U and the mean PIVKA-II increase was 77 1 ng/ml/mg warfarin. Demographic factors were not associated with warfarin response. For each 1 standard deviation (SD) lower value of plasma vitamin K-1, but not the other vitamin K variables, the INR rose 0.24 U (P less tha n or equal to 0.01). A higher usual vitamin K intake and plasma vitamin K-1 , and lower plasma vitamin K-1 2.3 epoxide, were all associated with a lowe r PIVKA-II increase over 4 d, Respective differences in PIVKA-II accumulati on per SD increase of each variable were -165, -218 and 236 ngl ml/mg warfa rin (all P less than or equal to 0.05). We concluded that dietary and bioch emical measures of vitamin K status were associated with early warfarin sen sitivity.