Black adults in the United States have two times the mortality rate from asthma complications than do white patients, a difference that is at least partly due to genetics. So optimizing treatment of asthma in this population is critically important.
That's why the AAFP National Research Network collaborated with a number of organizations, including Brigham and Women's Hospital and the Harvard Clinical Research Institute in Boston and Olmsted Medical Center in Rochester, Minn., on a study published in JAMA: the Journal of the American Medical Association(jama.jamanetwork.com) that examined treatment options for black adults with asthma, as well as whether a particular genetic variation could be linked to treatment response.
Researchers found that among black adults with asthma who were treated with inhaled corticosteroids (ICS), adding a long-acting beta agonist (LABA) didn't improve time to asthma exacerbation compared with adding tiotropium (Spiriva). In addition, allelic variation at the Arg16Gly locus of the beta2-adrenergic receptor (ADRB2) gene was not shown to be associated with response to treatment.
Previous research has suggested that Arg16Gly ADRB2 allelic variation might be associated with higher rates of adverse outcomes when LABAs are used for asthma treatment, particularly in black patients.
Wilson Pace, M.D., a co-investigator on the project and principal investigator for the AAFP, told AAFP News, "We proved that this alternative medication works as well as beta agonists but not better. African Americans who took the trial drug versus the other did just as well."
The multisite, open-label, randomized clinical trial was conducted from March 2011 through July 2013 and included 1,070 black adults in the United States with moderate to severe asthma who were eligible for or already receiving step 3 or step 4 combination therapy as defined by National Heart, Lung and Blood Institute guidelines(www.nhlbi.nih.gov). Of that total, 532 patients were assigned to tiotropium and ICS therapy, and 538 patients were assigned to LABA and ICS therapy.
Specifically, patients received ICS treatment plus either daily tiotropium or twice daily LABAs. All patients were genotyped, completed monthly questionnaires and visited with researchers at baseline and again one, six, 12 and 18 months later.
Aside from being confined to a single racial group, study limitations included the fact that it was an open-label study that was not placebo-controlled. Patients' asthma status also was based on physician diagnosis with no required objective testing, as is common in community practice.
In addition, the population in this trial had a relatively high treatment discontinuation rate (31 percent to 35 percent) and a relatively poor adherence rate (60 percent) to medications. However, that adherence rate is comparable with published "real-world" asthma medication adherence rates of 30 percent to 60 percent.
Three deaths occurred during the trial, Pace noted, two of which were related to asthma events and one that was attributable to medication nonadherence. "It was somewhat concerning that all of the deaths happened in the group using tiotropium and ICS treatment," he said.
Pace said no previous study of this size had examined how genetic variances among blacks affected their asthma rates. He added that this study was among information the FDA considered when the agency expanded the indications for tiotropium to include asthma treatment this past September. Previously, it was indicated only for treatment of chronic obstructive pulmonary disease.
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