Purpose: Imatinib adherence and persistence are key components of the successful treatment of Chronic Myeloid Leukemia (CML). In Belgium, there is no study assessing these behaviors at a national level. Our study aimed to provide the first nationwide measure and to identify associated pharmacy-based predictors (age, gender, comorbidities). We also assessed mortality and transplantation incidence according to adherence status.
Methods: Based on medico-administrative database linkage, we identified a retrospective Belgian cohort of 1194 patients diagnosed with CML between 2004 and 2016 and treated with imatinib. Adherence was measured over 24 months, considering the proportion of days covered (PDC). Persistence was measured as the time until discontinuation (gap of ≥90 days). Multivariable Poisson regression models with robust standard error were conducted to identify predictors associated with adherence (≥90% PDC). To identify factors associated with persistence, a multivariable Cox regression was performed.
Results: At six months, 60.3% of patients were adherent, declining to 41.5% at 12 months, and to 30.1% at two-year follow-up (n=998). Adherence was greater at a younger age (eg 31-40 years vs ≥75 years, adjusted prevalence ratio (aPR) 1.73; 95% confidence interval (CI): 1.09-2.77) and among patients with no comorbidity (0 vs ≥2 comorbidities (aPR 1.56; 95% CI: 1.11-2.19). The median persistence was 334.5 days (Q1:200-Q3:505.5); persistence at 24 months was 83.6% (n=998). Only age was associated with higher risk of discontinuation, with adjusted hazard ratio (aHR) of 6.05 for patients ≥75 years (95% CI: 5.52-6.58). Transplants and deaths mainly occurred in patients defined as non-adherent at 24 months.
Conclusion: This Belgian nationwide representative study revealed a critical low level of imatinib adherence, which decreased over time even though persistence was high at six months. We pinpointed pharmacy-based predictors that were easily identifiable by health care stakeholders in order to undertake interventions to improve adherence.