Severity of asthma. Because of the significant burden of symptoms and the risk associated with severe asthma it would seem logical that patients with severe disease would have a greater incentive for, and hence a greater likelihood of adhering to prescribed therapy. Conversely, it could be argued that for some asthmatic patients more symptomatic disease is the consequence of inadequate adherence to treatment. For example, Milgrom et al. (22) demonstrated in a study of paediatric asthmatic patients that prednisone bursts were more common in those patients who were found by electronic monitoring to be the least adherent to therapy with inhaled anti-inflammatory medication.
It has also been suggested that the immediate awareness of active asthma symptoms should serve as a cue for improved adherence to medication. Mann et al. (27) tested this hypothesis by measuring the relationship between patient adherence to four-times-daily beclomethasone and periods of increased severity of asthma. Ten adult patients with moderate-to-severe asthma were monitored over a 9-week period using an electronic device attached to the MDI to measure adherence to inhaled medication, and peak flow monitoring to measure airflow obstruction. The authors concluded that compliance with inhaled corticosteroids was not modulated by asthma severity (as measured by peak expiratory flow), or by patient-reported symptoms.
Patients' beliefs about inhaled corticosteroids and asthma. The relationship between beliefs about asthma and adherence to preventive therapy was clearly illustrated in a study by Adams et al. (28). The investigators interviewed adult patients in Wales, United Kingdom, using qualitative interviewing strategies and identified three common self-perspectives among this group: asthma deniers/distancers, asthma accepters, and pragmatics. Each of these perspectives was associated with very different beliefs held by the patients about the nature of asthma and the use of preventive medication. This analysis suggested that an asthmatic patient's self-perception of his or her disease may influence his or her adherence to preventive asthma therapy.
Parents and patients who are concerned about using corticosteroids may under-dose or discontinue long-term use in an effort to be "steroid-sparing". Boulet (29) conducted a telephone survey of over 600 adult asthmatic patients in Canada to find out about patients' perceptions about the role of ICS in the treatment of asthma and the potential side-effects of this therapy. The investigators found that patients frequently had misperceptions about the role of ICSs, even if they had recently used them. For example, over 40% of patients believed that ICS opened up the airways to relieve bronchoconstriction, while less than a quarter of the patients reported that ICS reduced airway inflammation. This fundamental misunderstanding of the mechanism of ICS suggests that these patients may also have failed to understand the underlying chronic inflammation that characterizes asthma and the need for preventive therapy. Forty-six per cent of the patients interviewed indicated that they were reluctant to take ICS regularly and only 25% of patients reported that they had discussed their fears and concerns about ICS with their primary care provider. Misconceptions about the side-effects and long-term consequences of ICS use were also common. However, when the true side-effects of inhaled corticosteroids were explained, most of the patients reported being reassured. Boulet (29) concluded that information about the safety and usefulness of ICS does not seem to have reached many patients with asthma. This study also suggests that health care providers should discuss with patients any possible concerns about ICS therapy that might interfere with adherence.
In a similar study conducted in the United States, Chambers et al. (30) surveyed 694 largely symptomatic asthmatic patients aged 18 - 49 years who had been prescribed ICS in 1995 - 1996. The most notable finding in this survey was the low level of self-reported adherence with therapy. Sixty-two per cent of patients reported less than regular twice-daily ICS use. Thirty-six per cent of the patients endorsed the option "some days I use it at least twice, but on other days I don't use it at all", and 22% reported that they no longer used ICS. Four per cent of patients claimed that they had never used ICS. Those who were less than fully adherent were asked to state their reasons for not using ICS, and the reason most frequently cited was that they used therapy only when they believed they needed it. This study suggests that many patients with asthma believe that their asthma is an episodic rather than a chronic disease, and that therapy is necessary only when there is disease exacerbation.
Psychological models of disease management have suggested that adherence to medication may be related to the patient's perceived vulnerability to the negative consequences of illness, with an increased sense of risk being associated with better adherence. In paediatric research, several studies have suggested that parents who consider their children's health to be fragile or vulnerable (whether based on real events or not) will be vigilant and will adhere to health care recommendations. Spurrier et al. (31) examined the relationship between the asthma management strategies used by 101 parents of children with asthma and the perceptions of these parents of their child's vulnerability to illness. The study found that after controlling for the frequency and severity of asthma symptoms, those parents who felt their child had greater vulnerability to illness were more likely to use regular preventive medications, take the child to the doctor and keep him or her home from school. The authors suggested that one possible explanation of this finding is that "parents who do not perceive their child to be medically vulnerable may discontinue administering regular medication…" (31).
Regimen factors in asthma therapy. A number of studies across a range of chronic diseases have found that certain characteristics of the prescribed treatment regimen are strongly associated with patient adherence. In general, the longer the duration of therapy, the more frequent the dosing, and the more complex the regimen (e.g. multiple devices or tasks), the poorer the adherence of the patient (32). Actual or perceived side-effects of treatment and the cost of therapy can also reduce adherence levels.
In recent years considerable effort has been directed towards developing an effective and safe once-a-day therapy for asthma because of its presumed advantage in promoting patient compliance. However, although there is convincing evidence that doses that must be administered more than twice a day lead to decreased adherence (19), the data are equivocal on the superiority of once-a-day dosing over twice-a-day dosing (33 - 35). Adherence considerations apart, once-daily asthma therapy appears to be preferable for most patients. Venables et al. (36) studied patient preferences in asthma therapy and found that 61% of patients expressed a preference for once-a-day treatment, 12% preferred twice-a-day treatment and 27% expressed no preference. While preference may not necessarily lead to improved compliance, it may well reduce the burden of therapy and enhance the quality of life of the patients.