Does the Timing of Warfarin Ingestion Affect the Time in Therapeutic Range in Patients With Metallic Prosthetic Valve?

Aim: Warfarin , a vitamin K antagonist, is the only approved oral agent to provide anticoagulation in patients with metallic prosthetic valves. Since effectively initiating and maintaining anticoagulation is challenging due to various factors , those patients undergo frequent periodic INR testing. The aim of this study was to investigate the effect of the timing of warfarin ingestion on the stability of anticoagulation. Materials and Methods: A total of 60 patients with metallic prosthetic valves were included in the study. First, all the patients were informed to take warfarin between 19:30 and 20:00 during the first month, then to take warfarin between 09:30 and 10:00 during the second month. All the patients underwent INR monitoring once every 15 days during the follow-up period. The time in therapeutic range (TTR) values for the first month and second month ( referred to as ‘first TTR’ and ‘second TTR’, respectively) were calculated separately using the Rosendaal method. Results: The mean age ( ± SD) of the patients was 59.6 ± 9.6 years and 36.7% (n=22) were male. There was no significant difference between the first TTR and second TTR values of the patients (66.23 ± 40.7% vs 64.12 ± 41.13%, p=0.783). The mean INR value in the first month was found to be significantly lower than in the second month (2.73 ± 0.53 vs 3.06 ± 0.47, p=0.001). Conclusion:.The study results showed that the timing of warfarin ingestion did not affect the stability of anticoagulation although taking the warfarin in the morning provided higher INR values.