Psychological predictors of adherence to oral hypoglycaemic agents: an application of the ProMAS questionnaire

Objectives: This study aimed to identify psychological predictors of oral hypoglycaemic agent (OHA) adherence and to compare adherence rates between a novel and well-known instrument, i.e. the Probabilistic Medication Adherence Scale (ProMAS) and Medication Adherence Report Scale (MARS-5). Design and main outcome measures: A longitudinal study design was applied with surveys at baseline and 6-month follow-up. At baseline, OHA adherence using the ProMAS and MARS-5, socio-cognitive determinants and demographics were assessed. At follow-up, the ProMAS was applied as outcome measure, on which socio-cognitive determinants and demographics were regressed using linear regression analysis. Results: The baseline and follow-up sample included 304 and 231 participants, respectively. When applying cut-off points of >= 15 for the ProMAS and >= 23 for the MARS-5, 47.4 and 89.5% adhered to their OHAs. Consistent predictors of better adherence comprised a low education, lower severity perceptions, and higher self-efficacy and intention. After correcting for baseline adherence, a low education and higher self-efficacy remained significant adherence predictors. Conclusions: Compared to the MARS-5, ProMAS data was less skewed, similar to objectively collected data, and yielded insights in a broader spectrum of (non)-adherence behaviours. Results stress the need for adherence improving interventions which particularly should target higher educated patients and patients with low self-efficacy, low intention and high severity perceptions.