AMVersus PMPostoperative Administration of Warfarin With a Mechanical Mitral Valve

Background:Currently, there are no guidelines regarding the optimal daily timing of inpatient warfarin administration. Objective:The purpose of this study was to determine whether dosing warfarin in the morning will have a significant impact on therapeutic international normalized ratio (INR) achievement compared with evening administration in mechanical mitral valve patients initiated on warfarin following cardiac surgery. Methods:This was a single-center, pre- and post-retrospective cohort conducted between 2014 and 2018. One-hundred fifty-four adult patients who underwent a mechanical mitral valve replacement or alternative cardiac surgery with a history of a mechanical mitral valve were enrolled. The primary outcome was achievement of therapeutic INR at any time point after initiation of warfarin. Pre-intervention administration timing was 6 pmand post-intervention timing was 10 am. Results:Baseline characteristics including age, sex, and race were similar between the 2 groups (P= NS for each characteristic). Therapeutic INR achievement was significantly improved at all time points following 10 amwarfarin administration compared with 6 pm(hazard ratio = 1.69; P= .005). Mean time-to-therapeutic INR was 7.37 days in the post-intervention group and 8.39 days in the pre-intervention group (P= .073). There were no significant differences in INR >4, bleeding, or thrombotic complications between groups. Conclusion and Relevance:This retrospective analysis suggests that there may be a postoperative benefit in therapeutic INR achievement in mechanical valve patients when dosing warfarin in the morning compared with evening administration. Large-scale studies should be conducted to further elucidate the potential benefit across more heterogeneous populations.