Nonadherence to disease modifying antirheumatic drugs in the first year after diagnosis: comparing three adherence measures in early arthritis patients

Objectives: The aim of this study was to compare three measurement methods for non-adherence to DMARDs in early arthritis patients: the Compliance Questionnaire Rheumatology (CQR), the intracellular uptake of MTX in the form of MTX-polyglutamates (MTX-PGs) and electronic measurement with Medication Event Monitoring Systems (MEMS).

Methods: DMARD naïve early arthritis patients were included in an ongoing cohort study. MEMS were used to measure adherence continuously, while every 3 months MTX-PGs were collected together with the CQR. The associations between the measures were estimated with Spearman rank correlations. Sensitivity and specificity of the CQR against a MEMS cut-off was compared at 3, 6, 9 and 12 months. The same applied to MTX-PGs against a MEMS cut-off and MTX-PGs against a CQR cut-off. For the association between MEMS, the CQR and MTX-PGs, a multilevel linear regression model was performed with age, gender, weeks of treatment and MTX dosage as covariates.

Results: We included 206 patients. Non-adherence measured with MEMS varied over time and between DMARDs. The CQR score was not associated with MEMS non-adherence at 3, 9 and 12 months. At 9 months, MTX-PGs was associated with MEMS non-adherence, as well as with the CQR. All correlations were below 0.30.

Conclusion: Associations between the three measures are weak. Explanations are individual differences in the uptake of MTX, and little variance in adherence between patients. Moreover, the measurement domains differ: perceptions (CQR), behaviour (MEMS) and pharmacokinetics (MTX).