Adherence to dornase alfa treatment among commercially insured patients with cystic fibrosis.

OBJECTIVE: To investigate adherence to dornase alfa therapy among commercially-insured patients with cystic fibrosis (CF) and to examine the impact of adherence on health and economic outcomes.

METHODS: This retrospective cohort analysis included CF patients with ≥1 dornase alfa (Pulmozyme) pharmacy claim between 1 October 2006 and 30 September 2008 and with continuous enrollment in the health insurance plan at least 1 year before and 1 year after their index dornase alfa claim. Adherence was measured with the medication possession ratio (MPR). Multivariate models were used to estimate the relationship between adherence and exacerbations, utilization, and cost.

RESULTS: Nine hundred and seven patients met the inclusion criteria. The mean age was 19.5 years (SD = 11.5) and 49.1% were female. Overall MPR was 0.59 and by age was 0.66 for patients of 5-12 years, 0.57 for 13-20 years, 0.54 for 21-30 years, and 0.56 for patients ≥31 years. Adherence was better in fall and winter than in spring and summer. There was no statistically significant difference in the proportion of patients with inpatient respiratory exacerbations across groups with low (<0.5), moderate (0.5-0.79), and high (≥0.8) adherence (24.5%, 22.3%, and 19.1%, respectively, p = 0.250). There was a trend toward higher total charges in more-adherent patients (mean $58,612 in the least-adherent group and mean $69,427 in the most adherent group, p = 0.107). In multivariate models, MPR was not significantly associated with the risk of inpatient respiratory exacerbations (hazard ratio = 1.16 for MPR <0.5 vs ≥0.8; 95% CI = 0.83-1.61).

LIMITATIONS: Study data were derived from insurance claims; adherence measures were based on prescription fills, not observed medication use.

CONCLUSION: Adherence to dornase alfa was generally low, but varied by age and season. Adherence was not found to be significantly associated with respiratory exacerbations or total charges, but was associated with shorter hospital length of stay.