Effect of vitamin K administration on rate of warfarin reversal

BACKGROUND: Vitamin K is reported to begin reversing warfarin within 6 to 12 hours, but this may occur sooner. We sought to determine the rate of international normalized ratio (INR) reversal following vitamin K and relationships with dose, route, and baseline INR. METHODS: We evaluated adult patients receiving vitamin K monotherapy for warfarin reversal. Post-vitamin K INRs through 48 hours were collected. Relationships between vitamin K dose and route and baseline INR on rate of reversal and complete reversal (INR < 1.5) were evaluated. Assessment was performed graphically using scatter plots with a line of best fit and a counting process model to determine variables associated with achieving complete reversal. RESULTS: A total of 469 post-vitamin K INRs from 235 patients were included. Time to first INR follow-up after vitamin K administration averaged 10.5 ± 4.2 hours. A significant decrease was detected in INR values in comparison to the baseline INR (3.0 ± 1.9 vs. 4.7 ± 2.2; p < 0.01). Rapid and steady INR change began immediately after vitamin K administration (0-4 hr). A high vitamin K dose and intravenous route were associated with rapid INR change and complete reversal (Vitamin K 10 mg [hazard ratio, 2.4; 95% confidence interval, 1.4-4.2] and IV route [hazard ratio, 1.8; 95% confidence interval, 1.3-2.6]); however, overall complete reversal at 24 and 48 hours was low (14.5% and 41.7%, respectively). Higher baseline INR was associated with rapid INR change and lower baseline INR with complete reversal. CONCLUSION: Vitamin K alone starts to reverse warfarin immediately. High vitamin K doses and intravenous route are associated with faster INR reversal. Baseline INR also influences rate of correction and frequency of achieving complete reversal.