Real-World Comparison of First-Line Treatment Adherence Between Single-Agent Ibrutinib and Acalabrutinib in Patients with Chronic Lymphocytic Leukemia

Purpose: Increased dosing frequency adversely affects treatment adherence and outcomes in chronic diseases; however, such data related to treatment adherence is lacking in chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). This study compared adherence between patients treated with ibrutinib (once-daily) versus acalabrutinib (twice-daily) as first-line (1L) therapy for CLL/SLL. Patients and Methods: Specialty pharmacy electronic medical records were used to identify adults with CLL/SLL initiating 1L ibrutinib or acalabrutinib between 01/01/2018 and 11/30/2020. Adherence was measured by the proportion of days covered (PDC) and medication possession ratio (MPR) and was compared between cohorts using odds ratios (ORs) obtained from logistic regression models adjusted for baseline characteristics. Results: Between 01/01/2018 and 11/30/2020, 1374 and 140 patients initiated ibrutinib and acalabrutinib, respectively. Based on PDC/MPR =80%, patients treated with once-daily ibrutinib were more likely to be adherent than those treated with twice-daily acalabrutinib (OR ranges: PDC: 1.04-1.76; MPR: 1.03-1.58). At 6 months, patients on ibrutinib had a 58-76% higher likelihood of staying adherent compared to patients on acalabrutinib (PDC: 75.9% for ibrutinib vs 63.6% for acalabrutinib, OR: 1.76, P=0.008; MPR: 76.8% vs 66.9%, OR: 1.58, P=0.036) with a similar trend noted for the entire line of treatment (LOT) (PDC: 53.0% vs 41.4%, OR: 1.53, P=0.021; MPR: 58.7% vs 47.1%, OR: 1.50, P=0.027). Conclusion: In this real-world analysis, CLL/SLL patients initiating 1L once-daily ibrutinib had > 50% higher treatment adherence than those initiating twice-daily acalabrutinib during their LOT. Given the importance of sustained adherence for disease control in CLL/SLL, dosing frequency may be an important consideration for patients and physicians.