Anticoagulation control in hospitalised patients on warfarin

Background: Anticoagulation control is a strong predictor of Iclinical outcomes for patients on warfarin. Aim: To identify instances of excessive anticoagulation in hospitalised patients on warfarin and to determine the causes of international normalised ratios (INRs) of 5 and above and the management strategies used to correct it. Method: An observational descriptive study undertaken at a teaching hospital over a 3-month period. Data were reviewed prospectively and retrospectively to measure the percentage of time patients were maintained within their target INR range while in hospital and to identify cases of excessive anticoagulation. Patients were divided into a control group (INR < 5) and a high INR group (INR ≥ 5). Possible causes of INRs of 5 and above and its management strategies were recorded. Results: Out of a total of 208 patients on warfarin identified in the geriatric, orthopaedic and cardiology wards, 144 patients met the study criteria. The mean percentage of time spent within, above and below the target INR range by the control group was 60%, 0% and 15%, and by the high INR group was 41%, 33% and 16%, respectively. In the high INR group, 26 possible causes of INRs of 5 and above were identified and the co-administration of roxithromycin and warfarin were implicated in 7 cases. Management strategies for INRs of 5 and above were compared between two stratified groups (INR 5-9 and INR ≥ 9). The management strategies adopted included warfarin dose reduction (83%; 86%), temporary withholding of warfarin (100%; 100%), administration of vitamin K (58%; 100%), fresh frozen plasma (13%; 43%) and prothrombin complex concentrate (8%; 29%). The time to return to the upper limit of the target INR range was INR 5-9 (1.6 SD 1.5 days) and INR ≥ 9 (0.5 SD 0.4 days). Conclusion: Anticoagulation control is difficult for hospital patients and drug interactions are an important contributing factor. The management strategies adopted to correct excessive anticoagulation followed the relevant guidelines