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Comparison of three medication adherence measures in patients taking warfarin

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Abstract

In order to improve warfarin adherence, we must first know the rate of non-adherence and the reasons for it. Assessment of warfarin adherence is important in improving patients’ warfarin-taking behavior and International Normalized Ratio (INR) control. This study aimed to compare three medication adherence measures in patients taking warfarin: the 8-item Morisky Medication Adherence Scale (MMAS), the 100-point Visual Analogue Scale (VAS) and medication refill adherence (MRA). A cross-sectional observational study was conducted in a convenience sample of 174 patients taking warfarin at an anticoagulation clinic. A survey questionnaire that included the MMAS, VAS, and demographic and warfarin-related clinical questions was administered to patients in English or Chinese depending on their preferences. The MRA and INR values were retrieved from hospital electronic databases. Most participants were adherent to warfarin as indicated by the three measures. A weak association was found between the MMAS and the other two adherence measures. The MMAS and MRA were associated with the percentage of INRs within range in the past 2 weeks. Moreover, the MRA was weakly associated with time within the therapeutic INR range in the past 3 months and 2 weeks. The findings provide insights into the differences among three medication adherence measures and may assist healthcare providers to select the most suitable measure for the assessment of warfarin adherence.

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Acknowledgments

We would like to acknowledge Professor Donald E. Morisky for providing us with the 8-item Morisky Medication Adherence Scale. We also thank Mr. Maung Maung Aung for his assistance in survey data collection and the pharmacists at the anticoagulation clinic of the Singapore General Hospital for patient referrals.

Conflict of interest

Nothing to declare.

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Authors and Affiliations

  1. Department of Pharmacy, Faculty of Science, National University of Singapore, Block S4, 18 Science Drive 4, Singapore, 117543, Republic of Singapore

    Ye Wang & Yu Ko

  2. Department of Pharmacy, Singapore General Hospital, C/O Allied Health Division, Bowyer’s Block B, Level 2, Outram Road, Singapore, 169608, Republic of Singapore

    Ming Chai Kong

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  1. Ye Wang
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  2. Ming Chai Kong
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Correspondence to Yu Ko.

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Wang, Y., Kong, M.C. & Ko, Y. Comparison of three medication adherence measures in patients taking warfarin. J Thromb Thrombolysis 36, 416–421 (2013). https://doi.org/10.1007/s11239-013-0872-5

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