Drug utilization and asthma control among young Danish adults with asthma. Analyses of trends and determinants.

UNLABELLED

This PhD thesis was performed during my employment at the Research Unit of General Practice in Odense, University of Southern Denmark. It comprises an overview of three papers, all published or submitted for publication in international peer-reviewed scientific journals.

BACKGROUND

Observational studies have revealed inadequate use of inhaled corticosteroids (ICS) among asthmatics. However, only limited data exist on whether ICS usage has changed over time. In addition, improved knowledge is needed on factors associated with ICS use and asthma control in order to identify subjects at risk of being inadequately treated.

AIMS

Among young adult Danish asthmatics we aimed: To investigate trends in ICS use and factors associated with ICS use during 1997-2006 (Study I). To investigate associations between socioeconomic status (education and income) and ICS use, and whether these associations were consistent over time during 1997-2005 (Study II). To investigate whether particular prescribing patterns of anti-asthmatic drugs were associated with clinically uncontrolled asthma (Study III).

METHODS

Three studies were carried out among Danish users of anti-asthmatic drugs aged 18-44 years. Study I (N = 106 757) and Study II (N = 97 665) were longitudinal studies based on repeated annual cross-sectional analyses on national register data. Study III (N = 357) was a cross-sectional study based on register and clinical data from a municipal cohort from Odense, Denmark.

RESULTS

Study I: We observed an annual increase in one year prevalence of ICS use from 67% in 2001 to 77% in 2006, occurring concurrently with the introduction of fixed dose combination therapy with ICS and inhaled long-acting beta-2-agonists. Still some 20-30% of subjects with a massive annual IBA consumption were not prescribed ICS. Factors associated with ICS use were high annual use of inhaled beta-2-agonists (IBA), female gender, age 18-24 years, use of leukotriene receptor antagonists, and use of drugs for rhinitis and specific immune therapy. Study II: High levels of education (OR 1.46, 95% CI 1.40-1.51) and income (OR 1.10, 95% CI 1.06-1.14) were found to be positively associated with ICS use with the most pronounced impact among 35-44 year-olds. Higher education showed an almost constant association with ICS use each year throughout the entire observation period, but high income did not demonstrate any statistically significant association with ICS use before 2001 (OR 1.10, 95% CI 1.02-1.18) with increasing ORs observed each year hereafter (OR 1.30, 95% CI 1.20-1.40 in 2005). Study III: A total of 96 of the clinically assessed subjects (26.9%) had uncontrolled asthma. An increasing association between uncontrolled asthma and an increasing annual quantity of inhaled short-acting beta-2-agonists (SABA) usage was demonstrated. Due to a substantial overlap in levels of SABA use among controlled and uncontrolled asthmatics this association was not strong enough to allow conclusions on individual asthma patients.

CONCLUSION

The results support previous findings by demonstrating a continuing inadequate use of ICS among young adult asthmatics with a consistent and high use of reliever therapy, which was associated with uncontrolled asthma. This apparent over-reliance on reliever therapy and possible non-adherence to ICS may indicate inefficient guideline implementation among patients and physicians, leaving room for further improvement. The clear indications of a socioeconomic gradient in ICS use further emphasizes that knowledge of patient-related factors associated with asthma treatment and asthma control is imperative for health care professionals to be able to identify subjects deserving special attention.