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Background: Reversal of overanticoagulation to minimize the bleeding risk is important in elderly inpatients receiving vitamin K antagonist therapy. However, no study has specifically focused on this population. The objective of this study is to evaluate whether guidelines based on American College of Chest Physicians recommendations for the management of overanticoagulation (international normalized ratio [INR] ≥5.0) can apply to elderly inpatients, and notably allow 24-hour INRs to return to the 1.8-3.2 range in this population. The influence of different factors on the vitamin K response also was evaluated., Methods: Inpatients aged ≥75 years with INR ≥5.0 were included in this observational study. INRs were assessed on the day of the overdosage (Day 0) and on the following day (Day 1)., Results: Of 385 Day 0 INRs ≥5.0 (239 patients; 86±6 years), 217 were managed according to recommendations, with a mean INR decreasing from 6.8±2.4 (range: 5.0-20.0) on Day 0 to 2.7±1.3 (range: 1.1-10.1) on Day 1 (P<.0001); 55% of INRs were within the 1.8-3.2 range, 20% <1.8, and 25% >3.2. In the subset of Day 0 INRs between 5.0 and 6.0, mean INR decreased from 5.5±0.3 to 2.7±1.0 (P<.0001) on Day 1 after oral administration of 1 mg vitamin K1 (n=121) and from 5.3±0.3 to 5.0±1.6 (P=.149) without vitamin K1 administration (n=48). Among covariates entered in the multivariate analysis, including co-medications, only the vitamin K1 dose influenced Day 1 INRs, with higher doses of vitamin K1 associated with Day 1 INRs <1.8 (P<.0001)., Conclusion: In elderly inpatients with INR ≥5.0, both vitamin K antagonist dose omission and vitamin K1 administration according to recommendations were effective in reversing overanticoagulation, allowing most INRs to return to the 1.8-3.2 range without excessive overcorrection. Therefore, American College of Chest Physicians recommendations may be applied to elderly inpatients., (Copyright © 2011 Elsevier Inc. All rights reserved.)