Evaluation of Warfarin Therapy and Achievement of Target Time in Therapeutic Range in Patients with Atrial Fibrillation at Cardiac Care Center Outpatient Clinic of Dr. Soetomo General Hospital

Warfarin remains an important oral anticoagulant for patients with atrial fibrillation (AF); however, achieving adequate anticoagulation requires appropriate prescribing, individualized dose adjustment, and regular monitoring. This study evaluated warfarin utilization, drug-related problems, and achievement of target time in therapeutic range (TTR) among patients with AF at the Integrated Cardiac Care Center Outpatient Clinic of Dr. Soetomo General Academic Hospital, Surabaya, Indonesia. This retrospective observational study reviewed the medical records of 106 eligible patients who attended the clinic between December 2023 and January 2024. Warfarin indications, dosing practices, international normalized ratio (INR) monitoring intervals, potential drug–drug interactions, and suspected adverse drug reactions were evaluated. TTR was calculated using the Rosendaal linear interpolation method. Appropriate indications for warfarin therapy were identified in 83.96% of patients. Mean concordance with the warfarin dosing algorithm was 43.20%, while 35.48% of 885 INR monitoring events occurred within the recommended monitoring intervals. Sixty-five potential drug–drug interaction events and nine bleeding events classified as Bleeding Academic Research Consortium (BARC) type 2 were documented. The mean TTR was 43.15 ± 25.28%, and only 18.87% of patients achieved a TTR ≥65%. These findings indicate that appropriate indications for warfarin therapy did not consistently correspond to adequate anticoagulation control. Warfarin management should therefore emphasize individualized dose adjustment, timely INR monitoring, and systematic medication review. These findings provide a basis for improving anticoagulation management services; however, the retrospective observational design precludes causal inference.