Asthma is a significant public health problem, with approximately 24.6 million Americans reporting current asthma in 2009 (1). Obesity prevalence has continuously increased over the last 30 years, reaching 33.8% among U.S. adults in 2007–2008 (2). A meta-analysis of prospective studies showed a dose-dependent relationship between increasing body mass index (BMI) and the risk of incident asthma (3). Understanding the influence of BMI and obesity on effectiveness of interventions to improve asthma control will help clinicians better care for obese patients with asthma.
The Better Outcomes of Asthma Treatment study, a randomized controlled trial in 612 adults with poorly controlled asthma, found that a shared treatment decision-making (SDM) intervention improved controller medication adherence and clinical outcomes (4). Given the increased attention to the links between obesity and asthma, we conducted post hoc analyses to investigate whether baseline BMI modified the SDM intervention effects on asthma medication acquisition outcomes (fill/refill adherence and regimen strength) and clinical outcomes in the follow-up year. We hypothesized that obese patients would have benefitted less from the SDM intervention than did overweight or normal weight patients. Some of the results reported here were previously reported in the form of an abstract (5).
Standard BMI categories were defined: normal (18.5–24.9 kg/m2, n = 132) and underweight (< 18.5 kg/m2, n = 7) combined, overweight (25–29.9 kg/m2, n = 185), and obese (≥ 30 kg/m2, n = 286).Using comprehensive pharmacy dispensing records, we computed continuous medication acquisition (CMA) indices (6–8) to measure fill/refill adherence for controller medications (inhaled corticosteroids, leukotriene modifiers, and others) and for long-acting β agonists (LABA) during the 12 months before and after randomization of individual participants. Controller and LABA medication regimen strength was measured by cumulative beclomethasone canister-equivalents (C-E) and salmeterol diskus-equivalents (D-E), respectively, using a standardized weighting methodology (9). Clinical outcome measures included the symptom subscale of the Juniper mini-Asthma Quality of Life Questionnaire (mini-AQLQ) (10), the Asthma Therapy Assessment Questionnaire (ATAQ) (11), asthma-related health care utilization, rescue medication use (via albuterol C-E), and lung function. Multivariable regression models were used to determine whether BMI modified the SDM intervention effect on these outcomes relative to usual care.
Compared with the controller regimen strength among normal weight SDM patients (0.036 ± 0.02 C-E), obese (0.05 ± 0.026 C-E, P = 0.027) and overweight SDM patients (0.048 ± 0.03 C-E, P = 0.0007) negotiated a higher daily controller dose. BMI negatively modified the SDM intervention effect on controller fill/refill adherence (P = 0.04; Figure 1). The SDM-related increase in controller CMA index among obese patients, relative to obese usual care patients, was smaller than observed for the other weight groups, although still in a favorable direction (β = 0.086; 95% confidence interval [CI], −0.03 to 0.202; P = 0.15). Obese SDM patients also received a smaller intervention benefit (but still significantly better than UC) in terms of the total number of salmeterol D-E dispensed (β = 1.82; 95% CI, 0.81 to 2.84; P = 0.0005) than SDM patients in other weight groups (interaction term P = 0.04).
Figure 1.
Increase in controller continuous medication acquisition (CMA) associated with shared decision-making (SDM) intervention, compared with usual care, by body mass index (BMI) category. *Normal weight: n = 139; β-coefficient for SDM versus UC: P value < 0.0001. †Overweight: n = 185; β-coefficient for SDM versus UC: P value = 0.0005. ‡Obese weight: n = 286; β-coefficient for SDM versus UC: P value = 0.15. Note that estimates based on multivariable regression models that were stratified by BMI category. Each model included group assignment, the five randomization balancing variables (4), and the baseline controller CMA.
BMI did not significantly modify the observed beneficial SDM intervention effects on any of the clinical outcomes. Like normal weight and overweight SDM patients, obese SDM patients demonstrated significantly better clinical outcomes compared with obese patients in usual care for asthma-related health care utilization, use of rescue medication (albuterol C-E), the FEV1 and FEV1/FEV6 ratio, and the odds of reporting no asthma control problems (a score of 0) on the ATAQ scale.
Although these analyses are exploratory, and thus, further research is needed, these results demonstrate that a shared decision-making approach to treatment choice can clinically benefit adult patients with poorly controlled asthma, regardless of BMI.
Supplementary Material
Acknowledgments
The authors acknowledge the BOAT study team and funding agency (NHLBI/NIH), as this study would have not been possible without their contribution to the original BOAT study. The authors acknowledge the contribution of Qiwen Huang, M.S., to the data analysis. The assistance of Kathy Stamm with document preparation is gratefully acknowledged.
Footnotes
Supported by the National Institutes of Health [Grants R01 HL69358, R18 HL67092, R01 HL094466–01A1S2]; and the Palo Alto Medical Foundation Research Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Heart, Lung, and Blood Institute or the National Institutes of Health.
Author Contributions: Conception and design, E.A., S.B.K., A.S.B., S.R.W.; analysis and interpretation, E.A., S.B.K., A.S.B., P.S., P.L., J.M., S.R.W.; drafting and/or reviewing the letter for important intellectual content, E.A., S.B.K., A.S.B., P.S., P.L., J.M., S.R.W.
Author disclosures are available with the text of this letter at www.atsjournals.org.
References
- 1.Centers for Disease Control and Prevention (CDC) Vital signs: asthma prevalence, disease characteristics, and self-management education: United States, 2001–2009. MMWR Morb Mortal Wkly Rep 2011;60:547–552 [PubMed] [Google Scholar]
- 2.Flegal KM, Carroll MD, Ogden CL, Curtin LR. Prevalence and trends in obesity among US adults, 1999–2008. JAMA 2010;303:235–241 [DOI] [PubMed] [Google Scholar]
- 3.Beuther DA, Sutherland ER. Overweight, obesity, and incident asthma. a meta-analysis of prospective epidemiologic studies. Am J Respir Crit Care Med 2007;175:661–666 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Wilson SR, Strub P, Buist AS, Knowles SB, Lavori PW, Lapidus J, Vollmer WM; Better Outcomes of Asthma Treatment (BOAT) Study Group Shared treatment decision making improves adherence and outcomes in poorly controlled asthma. Am J Respir Crit Care Med 2010;181:566–577 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Wilson SR, Knowles SB, Ma J, Ayala E, Strub P, Buist AS, Huang Q. Shared clinician-patient treatment decision making benefits both obese and non-obese patients. Am J Respir Crit Care Med 2010;181:A5791. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Steiner JF, Prochazka AV. Pharmacoepidemiology report: the assessment of refill compliance using pharmacy records: methods, validity, and applications. J Clin Epidemiol 1997;50:105–116 [DOI] [PubMed] [Google Scholar]
- 7.Steiner JF, Koepsell TD, Fihn SD, Inui TS. A general method of compliance assessment using centralized pharmacy records: description and validation. Med Care 1988;26:814–823 [DOI] [PubMed] [Google Scholar]
- 8.Choo PW, Rand CS, Inui TS, Lee ML, Cain E, Cordeiro-Breault M, Canning C, Platt R. Validation of patient reports, automated pharmacy records, and pill counts with electronic monitoring of adherence to antihypertensive therapy. Med Care 1999;37:846–857 [DOI] [PubMed] [Google Scholar]
- 9.Schatz M, Nakahir R, Crawford W, Mendoza G, Mosen D, Stibolt TB. Asthma quality-of-care markers using administrative data. Chest 2005;128:1968–1973 [DOI] [PubMed] [Google Scholar]
- 10.Juniper EF, Guyatt GH, Cox FM, Ferrie PJ, King D. Development and validation of the mini-asthma quality of life questionnaire. Eur Respir J 1999;14:32–38 [DOI] [PubMed] [Google Scholar]
- 11.Vollmer WM, Markson LE, O'Connor E, Sanocki LL, Fitterman L, Berger M, Buist S. Association of asthma control with health care utilization and quality of life. Am J Respir Crit Care Med 1999;160:1647–1652 [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.