Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Health Outcomes and Policy Research

Research Advisor

Song Hee Hong, Ph.D.


Raoul Arreola, Ph.D. Dick Gourley, Pharm.D. Jim Wan, Ph.D. Shelly White-Means, Ph.D.


Adherence, Asthma, Controllers, Cost-sharing, Outcomes


Prescription drug cost sharing is an effective tool to reduce the excessive drug consumption. However, many times it could have a negative impact on the drug utilization especially in case of chronic conditions. Chronic conditions such as asthma require appropriate utilization of controller medication to keep the inflammation and symptoms under control. Literature on asthma drug utilization has consistently reported underuse of controller drugs among asthma patients. The present study attempted to investigate the impact of prescription drug cost sharing levels on the controller adherence among the privately insured asthma population with moderate persistent asthma. The study also analyzed the relationship between adherence and asthma related health services utilization outcomes.

A retrospective analysis using the MarketScan administrative claims database was conducted for the years 2000 and 2001. Asthma patients that were stepped up to dual controller therapy in the study period and had no diagnosis for COPD or other respiratory conditions were included in the study. Study participants were also required to be in the age range of 5-65 and continuously enrolled in the health plan for the entire study period. Multivariate regression analysis using SAS 9.1 was performed to analyze the relationship between cost sharing levels and controller adherence. Linear probabilistic models were built to analyze the relationship between adherence and asthma related health services utilization.

A total of 1447 patients met the study criteria. The overall association between cost sharing and adherence was significantly negative. The drop in adherence to Inhaled Corticosteroids (ICS) with respect to cost sharing was greater after the patients were stepped to the dual controller therapy. Comparison of subgroups that used ICS+ LABA and ICS + LTRA revealed that the subjects ICS+LTRA subgroup are slightly more sensitive to the out of pocket costs. The analysis of adherence and health services utilization showed mixed results with reduction in ER visits but no association of hospital stay and SAB use.

Cost sharing levels had a negative impact on utilization of controller drugs. In terms of ICS adherence pre and post index periods, it can be concluded that the increased cost burden affected significantly even though the need to be adherent was increased. Based on the sub group analysis in the post-index period between the two add-on options, ICS + LTRA subgroup was more sensitive to the price changes. Adherence to controller regimen had a negative impact on ER visits however the data did not provide evidence in case of hospitalizations and SAB use.