Prolonged international normalized ratio during the first year of warfarin treatment

OBJECTIVE: Oral anticoagulants (OAC) are effective in the prevention of thromboembolic events but are underused. The 1st year following the beginning of vitamin K antagonists is associated with higher bleeding rate, especially in patients with international normalized ratio (INR) of >4, leading to discontinuation of OAC. We hypothesized that the decision to discontinue OAC during the 1st year in patients with events of overanticoagulation is not fully justified. SETTING: A retrospective study of the association between warfarin overanticoagulation during the 1st year of treatment and the outcome and complications in patients admitted to an internal medicine department with INR >4. SUBJECTS: A cohort of 249 patients was divided according to OAC treatment duration: ≤12 months (group I, n = 72; mean age, 79.1 years) and >12 months (group II, n = 177; mean age, 78.3 years). RESULTS: International normalized ratio upon admission was higher in group I (INR, 6.88 versus 6.16; P = 0.003). Patients in group I were overanticoagulated for a longer period (46.4% versus 18.5%; P < 0.001) but had lower time in therapeutic range (39.0% versus 60.2%; P = 0.001). The frequency of INR monitoring was higher in group I. The incidence of major and minor bleeding events and survival was similar. CONCLUSIONS: Patients who are admitted with INR >4 during the 1st year of OAC therapy are overanticoagulated for a longer period, have lower time in therapeutic range, but do not present with higher incidence of bleeding events, all compared with patients treated for longer than 12 months. Stricter INR monitoring and careful patient selection may prevent the discontinuation of OAC.