Predictors of medication adherence in people with rheumatoid arthritis: studies are necessary but non-validated measures of medication adherence are of concern

G. J. Treharne1,2, A. C. Lyons3, E. D. Hale2, K. M. J. Douglas2 and G. D. Kitas2,4,1

1 School of Psychology, University of Birmingham, 2 Department of Rheumatology, Dudley Group of Hospitals NHS Trust, Dudley, West Midlands, UK and 3 School of Psychology, Massey University, Auckland, New Zealand, 4 Department of Rheumatology, Division of Immunity and Infection, School of Medicine, University of Birmingham, Birmingham, UK

Correspondence to: G. J. Treharne, School of Psychology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. E-mail: G.J.Treharne{at}bham.ac.uk

SIR, We read with interest the study by Neame and Hammond [1] investigating medication beliefs and their relationship with medication adherence among people with rheumatoid arthritis (RA). The study tackles an important issue with serious implications for both patients and health professionals. However, there are some concerns that may limit the value of this study's conclusions.

Neame and Hammond's categorization of participants into adherent vs non-adherent groups [1] is questionable but is not discussed as a limitation of the study. Medication adherence was assessed by a single question (‘I often do not take my medicines as directed’) drawn from the Rheumatology Attitudes Index [2]; it is not stated whether this had been validated against any other measure of medication adherence. In addition, participants were not provided either with a benchmark for the frequency context of this question (‘often’) or with how exact they had to be with timing (‘as directed’). This may be particularly hard for patients to grasp for medications taken on a weekly basis, such as the very commonly used methotrexate. Furthermore, the distribution of answers across the five possible responses to the medication adherence question was not reported. This was skewed, given that only 27 patients (8%) self-reported being non-adherent out of a total of 331. This is considerably lower than the range reported in the literature (30–50%), which the authors themselves state.

We have previously carried out a similar study [3], also using the Beliefs about Medicines Questionnaire (BMQ) [4], among British RA patients. We measured medication adherence on a well-validated questionnaire scale: de Klerk et al.'s Compliance-Questionnaire-Rheumatology (CQR) [5]. Participants answer the CQR by rating their agreement on 19 items originally derived from interviews with patients, such as ‘If you can't stand the medicines you might say: ‘throw it away, no matter what’’. However, the CQR avoids emphasis on non-adherence, with 13 adherence-facilitating behaviours assessed; for example, ‘My medicines are always stored in the same place, and that's why I don't forget them’. The CQR compares well with electronic monitoring of medication container openings (across 6 months), which revealed a prevalence rate of non-adherent cases of 48% [5].

The main aim of Neame and Hammond's study [1] was to investigate the use of the BMQ among RA patients. Although they provided item means and distribution plots of the specific necessity and concerns subscale scores, they did not report basic psychometric properties, such as internal consistency and the correlation between the two subscales. In our study [3], the correlation between BMQ-specific necessity beliefs and concerns was negligible (r = –0.04), demonstrating acceptable independence. The necessity subscale demonstrated excellent internal consistency (Cronbach's {alpha} = 0.88) but the concerns subscale was below acceptable levels (Cronbach's {alpha} = 0.56), suggesting multiple factors may exist within concerns.

The general medication beliefs that RA patients hold also warrant investigation. These beliefs are measurable by the two additional subscales of the BMQ, both containing only four items. General harm beliefs are perceptions that medications are inherently dangerous; general overuse beliefs are perceptions that medications are prescribed too commonly [4]. Neame and Hammond [1] did not report on these general medication beliefs but did find that non-adherent patients had greater concerns about their medications than adherent patients. Hence, they suggest that rheumatologists could improve medication adherence by focusing on reducing specific medication concerns. However, in our multivariate regression of medication adherence measured by the CQR we found a different pattern of relationships [3]. Firstly, we controlled for demographic and medical factors. This showed that the greater the number of medications participants were taking, the higher their reported medication adherence. Secondly, specific medication concerns did not relate to medication adherence, contrary to Neame and Hammond's findings [1]. Instead, we found that higher specific necessity beliefs and lower general overuse beliefs concurrently related to higher medication adherence. This would suggest that RA patients on few medications and those who think that medications are prescribed too commonly or do not think their own medications are necessary are the cases who should be targeted to reduce medication non-adherence.

Finally, we agree with Neame and Hammond [1] that longitudinal studies are now required to investigate causality and determine whether medication beliefs predict long-term adherence to the many types of medications that RA patients are prescribed. We would recommend that future studies should employ a validated measure of medication adherence and consider the full range of medication beliefs from the general literature [4, 6] and RA-specific studies [7].

The authors have expressed no conflicts of interest.

References

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Accepted 24 May 2005