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The time course of, and variability in, return of the International Normalized Ratio (INR) to normal after excessive anticoagulation with warfarin have not been examined thoroughly. These researchers retrospectively studied a cohort of 633 patients treated in an outpatient anticoagulation unit who had received at least 60 days of warfarin therapy and, subsequently, had had at least one INR higher than 6.0. The patients had had warfarin withheld for at least 2 days; their INRs had been checked on day 2.
After 2 doses of warfarin were withheld, 37 percent of patients still had INRs of 4.0 or greater. Risk factors for persistently elevated INRs were: lower weekly warfarin maintenance dose, older age, higher index INR, decompensated congestive h…