Steinberg et al. Impact of adherence to interferons in the treatment of multiple sclerosis: a non-experimental, retrospective, cohort study. Clin Drug Investig. 2010;30(2):89-100. doi: 10.2165/11533330-000000000-00000.
BACKGROUND: RRMS is a chronic disease affecting about 400 000 people in the US characterized by increasing MSer disability and burden on society. While there is no cure for MS, pharmaceutical treatments exist that can limit the number of relapses a MSer experiences, and slow disease progression. One such class of agents used to treat RRMS are the interferons: interferon-beta-1a (Rebif and Avonex and interferon-beta-1b (Betaseron and Extavia). MSers must take these injectable medications regularly to achieve the optimal outcomes. However, MSer issues and potential adverse effects of the medication may prevent the patient from taking the medication as directed and lower adherence. To date, limited evidence exists regarding the effect of MSer adherence to interferon-beta therapies on clinical and economic outcomes.
OBJECTIVE: The purpose of this study was to explore the impact of MSer adherence to interferon-beta therapy on MS relapse rates and healthcare resource utilization.
METHODS: Using a non-experimental, retrospective cohort design, a sample population (n = 1606) was drawn from MSers identified in a database that includes both pharmacy and medical claims data. The study population was separated into two groups based on a measure of medication possession ratio (MPR*)-adherent and non-adherent patients, and adherence was defined as MPR > or =85% in a given year during the study period (2006-8). Key outcome variables included MS relapses and healthcare resource utilization. Data were analysed using parametric and non-parametric statistics, and regression modeling.
*Medication Possession Ratio (MPR) measures the percentage of time a patient has access to medication; i.e. takes the medication.
RESULTS: During the study period, the average MPR for all MSers on interferon-beta therapy varied from 72% to 76%. Only 27-41% of MSers in each year were considered adherent (i.e. MPR > or =85%) and only 4% of MSers had an MPR of > or =85% throughout the 3-year study period (2006-8). MSers who were adherent tended to have a lower risk of relapses over 3 years than non-adherent MSers. A significantly lower risk of relapses was found in 2006 (risk ratio [RR] 0.89; 95% CI 0.81, 0.97). Furthermore, an increasingly larger effect emerged between adherence and relapses when comparing adherent patients (MPR > or =85%) with subgroups of non-adherent MSers (<80%, <75%, <70%, <65% and <60%). The impact of adherence on emergency room (ER) visits also tended to suggest a lower risk during 2006, 2007 and 2006-8. During 2008, the risk for an ER visit was significantly lower for MSers adherent in 2007 (RR 0.78; 95% CI 0.61, 0.99). Inpatient admissions followed the ER trends, as MSers considered adherent in 2006 and 2007 tended to have a lower risk over 3 years. This result was significant for MSers adherent in 2007 (RR 0.79; 95% CI 0.65, 0.98).