Although adherence to treatment for a chronic condition may be in one’s best interest, many people do not adhere to prescribed treatment26
. We were specifically interested in ICS under use, since ICS medications are considered the most effective treatment for asthma, and IBA overuse, which is considered dangerous. Conversely, neither ICS overuse nor IBA under use would be considered especially clinically important because neither is associated with adverse asthma outcomes.
Our results show significant levels of nonadherence to prescribed asthma medication, and further show that when two medications are prescribed, approximately 50% are adherent to only one. Several predictors of medication-taking behavior were identified including income, education, and patient perception. The predictors varied depending on the medication prescribed and whether the issue was overuse or under use. Apter, et al. found that adherence to ICS was negatively associated with African American race, lower education, and lower income and positively associated with greater frequency of asthma symptoms27
. Our findings are interesting for the ways in which they do and do not fit this pattern.
We also observed a strong association between socioeconomic status (SES) and adherence, but not one that conforms to interchangeable assumptions about the measures used. SES may depend on a combination of variables including occupation, education, income, wealth, and place of residence28
, but typically, income and educational level are considered key measures. We found that ICS adherence was associated with higher income and that this relationship persisted even after accounting for lung function. However, ICS adherence was unrelated to educational level. Conversely, educational level was associated with IBA overuse, while income showed no association. Thus two measures of SES, education and income, demonstrated quite different associations with adherence, and may not completely reflect SES. Future exploratory work should use as many relevant SES variables to predict adherence behavior as possible to allow more complete analysis of the relationships among SES components and clinical or behavioral assessments.
We observed better lung function among ICS under users. It is possible that individuals with better lung function accurately perceive a decreased need for ICS medication. The mean FEV1
% predicted in ICS under users was 87%, well into the normal range. Although there is a range of ability to perceive airflow obstruction, it seems these subjects were aware of breathing comfortably and did not use their ICS medications as prescribed, perhaps because they felt well. Low asthma severity may not necessarily require treatment with ICS. The level of asthma severity can be inferred from spirometry except that both intermittent and mild persistent asthma specify FEV1
criteria of ≥80% predicted. These two categories are differentiated by frequency of symptoms. Our analysis showed no relationship between the frequency of daytime or nighttime symptoms and adherence to ICS. Conversely, IBA overuse was weakly associated with FEV1
% predicted and was significantly associated with perceived severity and with symptom frequency. When all three were tested in the same model, perceived severity, but neither lung function nor symptom frequency remained statistically associated with overuse. Overall, the perceived severity was weakly associated with FEV1
% predicted in this group, suggesting that perceptions drive behavior. One might assume that perceptions would vary with asthma severity, but Teeter et al has shown that the correlations between perceived symptoms and lung function are poor to modest at best29
Others factors could explain variability in adherence. DiMatteo et al. conducted a meta-analysis on studies of adults with chronic illnesses and found that depression correlated with poor adherence to therapy30
. Feldman et al found that 5% of a sample of adult asthmatics had mood disorders and others had high levels of depressive symptoms31
. We did not find depressive symptoms to predict nonadherence for either ICS or IBA. Others have found that IBA overuse was associated with poorer asthma control32
. Our measure of perceived control did not demonstrate an association with IBA use. Other factors that have been associated with asthma medication nonadherence are beliefs about asthma,33, 34
doubts about the usefulness of ICS medications32
, fear of side effects35–38
, and, among African-Americans, distrust of the healthcare system38, 39
. However, many of these studies were done in samples of children with asthma or their parents. Fewer studies of adult medication adherence have been done. One study found that adults who accepted that asthma is a chronic condition with acute flares were more likely to believe in the need for daily ICS medication, while those who perceived their asthma as symptom episodes took ICS sporadically40
. The type of provider (e.g. physician, nurse practitioner, or physician’s assistant) may also affect adherence. This type of data were not available as part of this study.
Our study was limited in that our relatively small cohort may lack sufficient power to detect modest associations. For example, we could not carry out stratified analyses or analyze ethnic-racial subgroup effects. We had a relatively large proportion of subjects (n=41) prescribed IBA but not an ICS medication, reflecting either prescribing inconsistent with general guidelines, or varying disease severity. Because this is a well-educated, middle aged, regionally-selected study group, our findings may not be generalizable to other regional settings or age-education patient mixes. Finally, though all medications were directly inspected, we relied on self-report of actual medication use and did not quantify adherence through objective methods such as electronic monitors or pharmacy refill records.
We explored the medication-taking behavior of a cohort of adults with asthma in their own home settings rather than in a clinical trial or clinic-based setting. Thus, our study provides a unique perspective on the choices made by individuals living with chronic asthma. A novel outcome of our analyses is the finding that perceptions of people with asthma drive the decision to adhere to prescribed ICS medication or to overuse IBA medication. Clinicians need to be aware that many patients will make their own appraisal of the need to follow medical advice based on their own perceived need for medications. Asthma education is essential to provide patients with the self-management knowledge necessary to keep asthma under good control and use medications to that advantage.