BACKGROUND:Regular use ofinhaledcorticosteroids(ICSs) can improveasthmasymptoms and prevent exacerbations. However, overalladherenceispooramong patients withasthma. Objective To estimate the proportion ofpoorasthma-relatedoutcomesattributable to ICS nonadherence.METHODS:We retrospectively identified 405adultsage 18 to 50 years who hadasthmaand were members of a large health maintenance organization in southeast Michigan between January 1, 1999, and December 31, 2001.Adherenceindices were calculated by using medical records and pharmacy claims. The mainoutcomeswere the number ofasthma-related outpatient visits, emergency department visits, and hospitalizations, as well as the frequency of oral steroid use.RESULTS:Overalladherenceto ICS was approximately 50%.Adherenceto ICS was significantly and negatively correlated with the number of emergency department visits (correlation coefficient [ R ] = -0.159), the number of fills of an oral steroid ( R = -0.179), and the total days' supply of oral steroid ( R = -0.154). After adjusting for potential confounders, including the prescribed amount of ICS, each 25% increase in the proportion of time without ICS medication resulted in a doubling of the rate ofasthma-related hospitalization (relative rate, 2.01; 95% CI, 1.06-3.79). During the study period, there were 80asthma-related hospitalizations; an estimated 32 hospitalizations would have occurred were there no gaps in medication use (60% reduction).CONCLUSIONS:Adherenceto ICS ispooramongadultpatients withasthmaand is correlated with severalpoorasthma-relatedoutcomes. Less than perfectadherenceto ICS appears to account for the majority ofasthma-related hospitalizations.
