Twenty-one studies with 983 patients were included in the review: 10 RCTs (534 patients) and 11 non-randomised prospective studies (449 patients).
The Jadad scores for all studies ranged from 0 to 7 out of a possible 8. The mean score was 3.4 for RCTs and 1.5 for non-randomised trials. The Downs scores for all studies ranged from 8 to 28 out of a possible 31. The mean score was 20 for RCTs and 13 for non-randomised trials.
Trials of patients taking acenocoumarol (2 trials, n=169).
When oral vitamin K (1 mg) was compared with withholding acenocoumarol, there was no difference between the treatments in the proportion of patients in the target range at 24 hours post-treatment (INR between 1.8 and 4.0) (pooled RR 0.9, 95% CI: 0.7, 1.1, P=0.48). Significantly more patients in the vitamin K groups had a sub-therapeutic INR less than 1.5 (pooled RR 5.7, 95% CI: 2.3, 14.0, P<0.001).
Trials of patients taking warfarin (8 trials, n=363).
Patients with a baseline INR of between 4.0 and 10.0 (n=321): the proportions of patients achieving an INR of 1.8 to 4.0 at 24 hours post-treatment was high at 82% (95% CI: 70, 93) for oral vitamin K, and was 77% (95% CI: 60, 95) for intravenous vitamin K. Patients receiving the intervention subcutaneously and those receiving placebo or observation were less likely to achieve the target INR at 24 hours: 31% (95% CI: 7, 55) and 20% (95% CI: 0, 47), respectively. A similar pattern of results was obtained for INR greater than 4.0 at 24 hours, where a much lower percentage of patients treated with oral and intravenous vitamin K had an INR in this range compared with groups given subcutaneous treatment or placebo. Only in patients given oral therapy did a significant number of patients have an INR less than 1.5: 6% (95% CI: 0, 12). Significant heterogeneity was observed in this analysis (I-squared range: 0% to 72%, P<0.001).
Patients with a baseline INR of greater than 10.0 (n=105, 42 in RCTs): 52% of patients who received vitamin K had an INR of between 1.8 and 4.0 at 24 hours, whereas 43% had an INR greater than 4.0; only 1 patient had an INR less than 1.5. Seventy-one per cent of patients given subcutaneous vitamin K had an INR greater than 4.0, compared with 48% of patients given oral therapy and 30% given intravenous treatment.
No information was available on adverse events and warfarin resistance.