Effect of Aspirin on the International Normalized Ratio in Elderly Patients with Atrial Fibrillation on Concurrent Warfarin Therapy

Abstract

Introduction:

Aspirin and warfarin are frequently taken together to enhance antithrombotic efficacy and prevent cardiovascular events. The initiation of aspirin in elderly patients with atrial fibrillation (AF) on warfarin therapy affects the International Normalized Ratio (INR). The aim of the study was to determine the changes in INR and the prevalence of INR adherence before and after aspirin initiation in elderly patients with AF on warfarin therapy.

Methods:

A cross-sectional study was conducted in the Anticoagulant Medication Therapy Adherence Clinic in Hospital Tuanku Ampuan Najihah from January to March 2021. In this study, we included elderly patients with AF on concurrent use of aspirin and warfarin for at least four weeks. A total of 350 patients with AF were screened for eligibility and 81 of them were included in this study. A data collection form was used to collect their demographic data as well as their INR before and after aspirin initiation. Descriptive statistics summarised the demographics and INR distribution. Paired t-test was used to assess the differences in INR before and after aspirin initiation.

Results:

Most of the patients were female (n=44, 54.3%), Malay (n=74, 91.4%), with a mean age of 74.94 ± 8.14 years old. There was a significant difference in the INR before and after aspirin initiation, 2.27 ± 0.79 and 3.59 ± 0.70, respectively (P<0.001). Before aspirin initiation, 32 (39.5%) patients achieved their targeted INR range of 2.0 to 3.0, meanwhile 33 (40.7%) and 16 (19.8%) patients had subtherapeutic and supratherapeutic INR ranges, respectively. In contrast, only 16 (19.8%) patients achieved their INR target range, after aspirin initiation. Furthermore, INR rose in 58 (71.6%) patients and 49 (60.5%) patients had their INR increased to above 3.0.

Conclusion:

This study showed that aspirin initiation increased the INR significantly in elderly patients with AF on warfarin therapy. Thus, healthcare professionals should monitor INR closely when aspirin is prescribed concurrently with warfarin in elderly patients with AF. Improvements in the patient counselling points checklist have to be made to ensure optimal health outcomes in and prevent potential bleeding incidence.