Scientists evaluated the therapeutic options for asthmatic black adults and the possible association between genetic variations and response to treatment. Researchers from the American Academy of Family Physicians (AAFP) National Research Network partnered with various institutions for the study, including the Olmsted Medical Center in Rochester in Minnesota and the Brigham and Women’s Hospital and Harvard Clinical Research Institute in Boston.
The team found that therapies based on long-acting beta-adrenoceptor agonists (LABA) were not as effective in black patients as they seem to be in white patients.
The study, “Anticholinergic vs Long-Acting β-Agonist in Combination With Inhaled Corticosteroids in Black Adults With Asthma, The BELT Randomized Clinical Trial,” was published in JAMA: the Journal of the American Medical Association.
Asthma is a chronic inflammatory disease that affects over 22 million individuals in the United States as of 2013, according to the Centers for Disease Control and Prevention (CDC). The condition can be identified by narrowed and swollen airways caused by mucus accumulation in the lungs, making it difficult to breathe.
Asthma has no cure, but a number of drugs, including long-acting beta-adrenoceptor agonists (LABA), such as salbutamol, as well as oral corticosteroids (ICS), are available to relieve the symptoms. But patients can respond differently to asthma therapies. In this respect, the efficacy and safety of LABAs have been questioned in black adults when compared with the white population.
The different response to treatment between ethnic groups was hypothesized to be partially associated with genetic variations, particularly in the Arg16Gly locus of the ADRB2 gene that could eventually influence the response to LABA-based treatment in black patients.
The team conducted a clinical trial between March 2011 and July 2013 to investigate this disparity in treatment response and compare the effectiveness and safety of tiotropium compared to LABAs, when used in combination with inhaled ICS in asthmatic black patients. The team also assessed if the genetic variation at the Arg16Gly locus of the ADRB2 gene was linked to the response to treatment.
A total of 1,070 black Americans with moderate to severe asthma were included in the trial. The patients were qualified to receive step 3 or step 4 combination therapies as defined by the National Heart, Lung and Blood Institute guidelines.
Among the patients, 532 were treated with ICS and daily tiotropium therapy, while the remaining 538 patients were under ICS and twice-daily LABAs treatment. All patients underwent a genetic screening, completed a monthly questionnaire, and participated in scheduled visits at baseline, then at 1, 6, 12, and 18 months into treatment.
The results suggested that asthma exacerbations in black patients treated with ICS didn’t improve if LABA was added to the therapy instead of tiotropium. Furthermore, genetic variations in Arg16Gly locus of the ADRB2 gene showed no particular link with response to treatment.
Three deaths occurred during the trial. Two were attributed to asthma events and one was related to medication nonadherence. “It was somewhat concerning that all of the deaths happened in the group using tiotropium and ICS treatment,” said Dr. Wilson Pace, a co-investigator on the project and principal investigator for the AAFP in a news release.
There were limitations of the study: it wasn’t placebo-controlled; the asthma status was solely determined by physicians; and patients showed a relatively high treatment-discontinuation rate (31 to 35 percent) and a relatively poor adherence rate (60 percent) to treatment.
Overall, the results of this large-scale study did not support the superiority of LABA plus ICS treatment if compared with tiotropium plus ICS in asthmatic black patients. The findings allowed the FDA to expand the indications for tiotropium, indicated as a therapy for chronic obstructive pulmonary disease (COPD), last September to also include asthma treatment.
“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,” Pace said.
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