Methotrexate compliance among patients with rheumatoid arthritis: the influence of disease activity, disease duration, and co-morbidity in a 10-year longitudinal study

Methods: Using prescription data, we conducted a 10-year longitudinal study among RA patients who were first-time MTX users. MTX compliance was expressed as the continuous measure of medication gaps (CMG), that is the proportion of treatment gaps compared with the total observation period stratified by age, sex, C-reactive protein (CRP), haemoglobin, co-morbidity, concurrent medication, and disease duration. Multiple linear regression analysis was used to assess the influence of disease activity, disease duration, and co-morbidity on compliance. Results: A total of 941 RA patients redeemed 7501 MTX prescriptions during our study period. Overall, the patients had gaps in 12.3% of the observation period corresponding to a mean period not covered with MTX of 1.5 months/year if all participants were followed for 1 year. Patients with CRP > 32 mg/L had a lower mean CMG than patients with CRP < 8 mg/L [adjusted CMG difference -0.04, 95% confidence interval (CI) -0.07 to - 0.02]. Patients with a disease duration < 1 year had a lower mean CMG than patients with a disease duration between 1 and 5 years (adjusted CMG difference 0.01, 95% CI -0.01 to 0.04). Patients with a diagnosis of ulcer/mild liver disease had a higher mean CMG than patients without this diagnosis (adjusted CMG difference 0.04, 95% CI 0.004-0.084). Conclusion: MTX compliance was generally high among RA patients. Compliance decreased with increasing disease duration, low to moderate disease activity, and the presence of a diagnosis of ulcer/mild liver disease.