Exploring the Agreement Between Self-Reported Medication Adherence and Pharmacy Refill-Based Measures in Patients with Kidney Disease

Abstract

Karumathil M Murali,1,2 Judy Mullan,2 Steven Roodenrys,3 Hicham I Cheikh Hassan,1,2 Maureen A Lonergan1 1Department of Nephrology, Wollongong Hospital, Wollongong, NSW, Australia; 2School of Medicine, University of Wollongong, Wollongong, NSW, Australia; 3School of Psychology, University of Wollongong, Wollongong, NSW, AustraliaCorrespondence: Karumathil M Murali, Department of Nephrology, Wollongong Hospital, Wollongong, NSW, 2500, Australia, Tel [phone], Fax [phone], Email [email protected]: To assess the quantitative and categorical agreement between two methods of measuring medication adherence: pharmacy refill-based medication possession rates and self-reported medication adherence scale.Background: Categorisation of adherence metrics using empirical cut-off scores can lead to misclassification, which can be overcome by expressing adherence as a continuous variable. Pharmacy refill-based adherence can be reported as actual rates, but the validity of expressing self-reported medication adherence scores as a continuous variable to reflect adherence is unknown and its quantitative agreement with refill-based adherence rates untested.Methods: Patients with kidney disease, including dialysis patients, from Illawarra Shoalhaven region of New South Wales, Australia were recruited between January 2015 and June 2016 to this cross-sectional study. Medication adherence was assessed using the self-reported Morisky Medication Adherence Scale (MMAS) and two pharmacy refill-based measures, Medication Possession Ratio (MPR) and Proportion of Days Covered (PDC) for antihypertensives and cardiometabolic drugs. Categorical and quantitative agreement between self-reported adherence and pharmacy refill-based adherence were assessed using tests of trend, analysis of covariance (ANCOVA), Cohen’s kappa and Bland-Altman analysis.Results: We recruited 113 patients. There was a significant declining trend of MPR (p < 0.001) and PDC (< 0.001 for antihypertensives, p = 0.004 for cardiometabolic) scores among categories with worsening MMAS adherence. Adjusted ANCOVA showed significant association between self-report and pharmacy refill-based adherence (p < 0.001). Weighted Cohen’s kappa statistics showed fair agreement between the self-report and pharmacy refill-based categories. Bland-Altman’s analysis showed less than 5% of cases were outside the limits of agreement (− 0.36 to 0.27) and the bias for MMAS was negative (− 0.05 to − 0.09), indicating MMAS did not overestimate adherence.Conclusion: There is modest agreement between pharmacy refill-based measures and self-report MMAS measures when assessed categorically or quantitatively. Assessing adherence as a continuous variable should be considered to overcome the challenges associated with categorization of adherence based on arbitrary thresholds.Keywords: medication adherence, patient compliance, self report, medication possession rate, proportion of days covered, kidney failure, chronic kidney disease

Keywords

• medication adherence patient compliance self report medication possession rate proportion of days covered kidney failure chronic kidney disease