Portuguese version of the Medication Adherence Report Scale (MARS-9): Validation in a population of chronic pain patients.

Aim: The aim of present study was to perform the translation, cultural adaptation, and validation of the Medication Adherence Report Scale (MARS-P9) for the European Portuguese language in a sample of chronic pain patients.

Methods: A Portuguese version of the nine-item MARS (©Professor Rob Horne) scale (MARS-P9) was constructed through a process of translation, back translation, and experts' panel evaluation. A total of 141 chronic pain patients were subsequently evaluated at four time assessments during a 1-year pain medication treatment. The protocol interview included the assessment of pain intensity and interference (BPI), clinical outcomes and quality of life (S-TOPS), and MARS-P9.

Results: The internal consistency coefficient was acceptable for the total scale (α = 0.84). Exploratory factor analysis revealed a two-factor structure (intentional and unintentional nonadherence) that explained 61% of the variance. Convergent and discriminant validity were demonstrated by correlations between MARS scores and pain interference (r = 0.180, P ≤ 0.01) and S-TOPS (r = 0.242, P ≤ 0.05).

Conclusion: MARS-P9 has been shown to be an adequate instrument for Portuguese researchers and clinicians to assess the pattern of adherence during the management of chronic pain.