Adherence to laboratory monitoring among people taking oral drugs for multiple sclerosis: A Canadian population-based study

Objective: To examine laboratory testing adherence by persons initiating an oral disease-modifying therapy (DMT) for multiple sclerosis (MS). Methods: Population-based health administrative and laboratory data were accessed in British Columbia, Canada, to identify everyone filling their first prescription for dimethyl fumarate (DMF), fingolimod or teriflunomide (2011–2015). The proportion of people adherent to each drug monograph’s recommended laboratory monitoring schedule, pre- and on-DMT, was estimated. The association between patient characteristics and adherence was examined using multivariable logistic regression. Results: A total of 1016 people were included (DMF 567, fingolimod 253 and teriflunomide 196). The proportions of people adherent to pre-DMT liver and lymphocyte tests ranged from 88% to 91% and 91% to 94%, respectively, while 77% adhered to pre-DMF urinalysis. Adherence to the first on-DMT liver test was 89% for DMF (within 6 months), 61% for fingolimod (within 3 months) and 40% for teriflunomide (within 1 month). Men were less likely than women to have pre-DMF urinalysis (adjusted odds ratio (aOR); 95% confidence interval (CI): 0.40–0.95) or on-DMF liver (aOR: 0.46; 95% CI: 0.23–0.95) or lymphocyte (aOR: 0.47; 95% CI: 0.22–0.98) tests. Conclusions: Adherence to recommended laboratory testing was high (>77%) before oral DMT initiation, but lower once on drug. There is a need to understand the long-term consequences of suboptimal laboratory monitoring and sex differences in the DMT-treated MS population.