Adding dust mite sublingual allergen immunotherapy (SLIT) to maintenance asthma medications significantly prolonged the time to a first asthma exacerbation during planned inhaled corticosteroid reduction, but mild to moderate adverse events were common, researchers reported.

The trial included 834 adults with house dust mite allergy-related asthma not well controlled by inhaled corticosteroid (ICS), randomized to treatment with placebo or a once-daily dust mite SLIT tablet in one of two doses. Compared with placebo, the addition of dust mite SLIT at either dose to maintenance medications significantly improved time to first moderate or severe asthma exacerbation during ICS reduction at 6 months, with increases seen in allergen-specific immunoglobulin G4 (IgG4), according to J. Christian Virchow, MD, of Germany's University of Rostock, and colleagues.

"Together, the data confirm an effect on both current asthma control and future risk," they wrote in Journal of the American Medical Association.

House dust mite (HDM) sensitization was shown to occur in as many as half of asthma patients in a pediatric study, and house dust mite exposure is a well recognized driver of asthma severity, the researchers wrote.

The FDA has approved SLIT treatments in tablet form for both ragweed and grass pollen to treat patients with allergies.

"Previously, the HDM SLIT tablet has proven to be effective in reducing the requirement for ICS and in reducing allergic rhinitis symptoms and need for pharmacotherapy among patients with known HDM respiratory allergic disease," the researchers wrote. "However, to our knowledge, the effect on risk of asthma exacerbations has not been addressed previously."

The trial was conducted from August 2011 to April 2013 at 109 sites in 13 European countries. Patients were randomized in a 1:1:1 manner to once daily treatment with placebo (n=277), HDM SLIT at a dosage of 6 SQ (n=275), or HDM SLIT at a dosage of 12 SQ (N=282), in addition to ICS and the short-acting β2-agonist salbutamol.

Exclusion criteria included forced expiratory volume in 1 second (FEV1) of less than 70% of predicted value or hospitalization due to asthma in the 3 months before randomization. A total of 693 participants completed the trial. The authors reported that, compared with placebo, rates of moderate or severe asthma exacerbation with HDM SLIT were significantly reduced (hazard ratio 0.72, 95% CI 0.52-0.99, P=0.045) in the 6SQ-HDM group and in the 12 SQ-HDM group (HR: 0.69, 95% CI 0.50-0.96, P=0.03).



Also, the absolute risk differences based on the observed data (full analysis set) in the active groups versus the placebo group were 0.09 (95% CI 0.01-0.15) in the 6SQ-HDM group and 0.10 (95% CI 0.02-0.16) in the 12SQ-HDM group.

No difference in efficacy was seen between the two active groups. Compared with placebo, there was a reduced risk of exacerbation with deterioration in asthma symptoms n the 6SQ-HDM group (HR 0.72, 95% CI 0.49-1.02, P=0.11, and the 12SQ-HDM group (HR 0.64, 95% CI, 0.42-0.96, P=0.03) and a significant increase in allergen-specific IgG4.

A total of 72% participants reported adverse events in a dose-dependent manner, with the majority of these events being mild. The three most commonly reported events were oral pruritus, mouth edema, and throat irritation.

Between 79% and 85% of participants reported improvements in asthma control and quality of life scores assessed by questionnaire, including those taking placebo.

Study limitations included "the operational definition of a moderate asthma exacerbation that, to our knowledge, was used for the first time."

In an accompanying editorial, Robert A. Wood, MD, of Johns Hopkins University School of Medicine in Baltimore, wrote that the exclusion of patients with severe or unstable asthma was another significant study limitation, as was the possibility for unblinding with SLIT therapy, due to the high frequency of adverse events.

Still, the findings should be considered "important and clinically relevant," Wood stated, adding to the evidence that single allergen immunotherapy -- common in Europe but not the U.S. -- has clinical efficacy in a range of patients.

"In this study, 66% of the participants were sensitized to other allergens in addition to HDM, with no differences in outcome detected between those patients and those monosensitized to HDM, demonstrating the clinical efficacy of single allergen immunotherapy even among polysensitized patients," he wrote.

Wood concluded that rigorous immunotherapy studies are still needed, "as there is still a great deal of room for refinement in the practice of immunotherapy. As research continues and these therapies enter clinical practice, the goal should be to optimize each patient's immunotherapy regimen and disease control, taking personal preferences into account, and ideally to develop additional patient profiling using specific biomarkers to further personalize the use of these treatment options."

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