House dust mite sublingual immunotherapy may be effective for allergic asthma

House dust mite sublingual immunotherapy tablets reduced inhaled corticosteroid use among patients with mild to moderate allergic asthma, according to a systematic review in The Journal of Allergy and Clinical Immunology: In Practice.

However, the evidence for whether house dust mite (HDM) sublingual immunotherapy tablets (SLIT) reduced asthma exacerbations remained limited, Chamard Wongsa, MD, internal medicine lecturer and instructor in the division of allergy and clinical immunology at Faculty of Medicine Siriraj Hospital, Mahidol University in Bangkok, and colleagues wrote.

Although HDM SLIT has shown efficacy for treating allergic rhinitis, it is recommended for patients with sub-optimally controlled allergic asthma despite limited evidence.

Therefore, the researchers conducted a systematic review to assess the efficacy of HDM SLIT on asthma outcomes. The analysis included five randomized controlled trials (RCTs) of patients with asthma (n = 2,475) and two RCTs of patients with allergic rhinitis (AR) with or without asthma (n = 1,606). Also, six studies included adults and adolescents, and one included children.

Three studies examined the efficacy of HDM SLIT — in doses of 6 standardized quality (SD) HDM tablets or 12 SD HDM tablets — on inhaled corticosteroid (ICS) use.

In the first study, involving 604 patients aged 14 years and older with mild to moderate asthma concomitant with HDM AR, 34% of those receiving the 6 SQ HDM dose completely discontinued ICS, compared with 21% in the placebo group.

In a post hoc analysis comprising 108 patients with partly controlled asthma, 59% of patients on the 6 SQ-HDM dose reduced ICS use by 75% to 100%, with 45% withdrawing ICS completely without losing control of their asthma.

A study of 109 children aged 5 to 15 years with mild or moderate asthma, however, saw no significant differences in outcomes between HDM SLIT and placebo in reducing ICS usage.

Two studies investigated the efficacy of HDM SLIT on asthma exacerbation, and in one researchers observed a reduction in risk for asthma exacerbation while reducing ICS dose with both the 6 SQ HDM dose (HR = 0.72; 95% CI, 0.52-0.99) and 12 SQ HDM dose (HR = 0.69; 95% CI, 0.5-0.96). However, based on a lack of significant findings in the second study, the researchers concluded that the role of this treatment for patients with partly controlled moderate to severe asthma remains questionable.

Yet 6 SQ HDM tablets significantly improved Asthma Control Questionnaire and Asthma Quality of Life Questionnaire (AQLQ) scores in one study’s subgroup of patients with partly controlled mild to moderate asthma. A second study found significant improvements in AQLQ emotion domain scores with a mean difference of 0.42 (95% CI, 0.15-0.69).

The 6 SQ HDM tablets also significantly improved forced expiratory volume in 1 second and forced vital capacity with a mean difference of 103.02 mL (95% CI, 29.16-176.88) and 117.27 mL (95% CI, 110.85-123.68) compared with placebo in one study, although three of the other studies revealed no significant change in lung function.

In the first of the two studies that looked at patients with AR with or without asthma, asthma symptom scores improved by 65% with the 12 SQ HDM dose and by 53% with the 6 SQ HDM dose compared with placebo after 24 weeks.

The second study, involving 1,482 participants aged 12 years and older, found a 25% improvement after 52 weeks using 12 SQ HDM tablets, with a difference of least-square mean asthma symptom score of –0.46 (95% CI, –0.83 to –0.1).

Most of the studies indicated that SQ HDM SLIT induced specific immunoglobulin G4 production as early as 8 weeks after treatment initiation, typically improving rhinitis symptoms in patients with AR. One study also found that 6 SQ HDM tablets improved airflow limitation correlated with CT parameters and exhaled nitric oxide level.

The percentages of participants in the studies’ intervention groups who reported at least one adverse event ranged from 39% to 96.4%, with the most common symptoms including local swelling of the mouth, lips, tongue or ear, in addition to pruritis and some gastrointestinal discomfort. In one study, seven participants were treated with epinephrine. No deaths were reported.

Although HDM SLIT tends to be effective in improving asthma outcomes in HDM AR patients with well or partly controlled mild to moderate asthma, the researchers wrote, further studies should investigate which asthma outcomes to measure and the asthma severity levels that should initiate treatment.