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.