Prevalence and factors associated with polypharmacy among people with multiple sclerosis (PwMS) receiving outpatient rehabilitation: A cross-sectional study

BACKGROUND: Over 2.8 million people are living with multiple sclerosis (MS), many with comorbidities requiring pharmacologic intervention. This can lead to increased medication use and subsequent polypharmacy, which is associated with numerous adverse outcomes. The objective of this study is to describe medication use, the extent of polypharmacy, and correlates with sociodemographic, health behaviour and clinical/comorbidity factors in PwMS treated in an outpatient Physical Medicine and Rehabilitation (PM&R) setting. METHODS: This cross-sectional study uses retrospective chart data from all PwMS referred for rehabilitation at the largest MS tertiary care clinic in Canada between December 2021 and December 2023. Data on sociodemographic factors, clinical factors, and health service use were collected and analyzed using descriptive statistics and log-binomial regression modelling. RESULTS: A total of 475 PwMS were included, of which 343 (72.2%) had polypharmacy and 120 (25.2%) had hyper-polypharmacy (>10 concurrent medications). Most PwMS (62.3%, n = 296) were female, and the average age was 51.3 years (SD=11.8). PwMS with polypharmacy were taking an average of 8.9 medications (SD=3.5), compared to 3.0 on average (SD=1.1) among those without polypharmacy. Moreover, PwMS with polypharmacy had more comorbidities (median=3 vs 1, IQR=2-5 vs 1-3, p < 0.0001) than those without polypharmacy. Results from log-binomial logistic regression models found cannabinoid use (PR=1.43, 95% CI=1.25-1.64), physical comorbidities (PR=1.32, 95% CI=1.17-1.49), mental health comorbidities (PR=1.20, 95% CI=1.09-1.32), and cognitive symptoms (PR=1.15, 95% CI=1.02-1.30) to be associated with an increased prevalence of polypharmacy among PwMS. Full- or part-time employment was associated with a decreased prevalence of polypharmacy (PR=0.84, 95% CI=0.72-0.97). CONCLUSIONS: A high prevalence of polypharmacy was found among PwMS receiving rehabilitation. A variety of sociodemographic, behavioural, and clinical/comorbidity factors were associated with polypharmacy. Rehabilitation physicians treating PwMS should consider and address polypharmacy guided by established tools. Further research with a larger sample size and robust study design is needed to disentangle major risk factors and trajectories of polypharmacy among PwMS.