Adherence to the immunomodulatory drugs for multiple sclerosis: Contrasting factors affect stopping drug and missing doses

Background: Long-term immunomodulatory drug (IMD) treatment is now common in multiple sclerosis (MS). However, predictors of adherence are not weil understood; past studies lacked lifestyle factors such as alcohol use and predictors of missed doses have not been evaluated. We examined both levels of non-adherence - stopping IMD and missing doses. Methods: This longitudinal prospective study followed a population-based cohort (n = 199) of definite MS patients in Southern Tasmania (January 2002 to April 2005, source population 226 559) every 6 months. Baseline factors (demographic, clinical, psychological and cognitive) affecting adherence were examined by logistic regression and a longitudinal analysis (generalized estimating equation (GEE)). Results: Of the 97 patients taking an IMD (mean follow-up=2.4 years), 73% (71/97) missed doses, with 1 in 10 missing > 10 doses in any 6-month period. Missed doses were positively associated with alcohol amount consumed per session (p = 0.008). A history of missed doses predicted future missed doses (p < 0.0005). Over one-quarter (27/97) stopped their current IMD, which was associated with lower education levels (p = 0.032) and previous relapses (p = 0.05). No cognitive or psychological test predicted adherence. Conclusions: There were few strong predictors of missed doses, although people with MS consuming more alcoholic drinks per session are at a higher risk of missing doses. Divergent factors influenced the two levels of non-adherence indicating the need for a multifaceted approach to improving IMD adherence. In addition, missed doses should be assessed and incorporated into clinical trial design and clinical practice as poor adherers could impact on clinical outcomes.