LOS ANGELES (FRONTLINE MEDICAL NEWS) – A sublingual immunotherapy tablet for house dust mite–induced allergic rhinitis achieved clinically meaningful improvement in symptoms along with less use of rescue medications and a favorable safety profile in a pivotal phase III trial, Dr. Hendrik Nolte reported at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.

The double-blind, 52-week randomized trial included 1,482 North American adults and adolescents.

“This was the largest clinical trial ever conducted with sublingual therapy in North America, and the first successful North American trial of a house dust mite sublingual immunotherapy tablet. It confirms results from previous large European trials,” noted Dr. Nolte of Merck, which is collaborating with the Danish company ALK in developing this therapy.

The sublingual immunotherapy (SLIT) tablet, known for now as the 12 SQ HDM SLIT-tablet, has been approved by European regulatory authorities for treatment of adults with house dust mite (HDM) allergic rhinitis or HDM allergic asthma. Based upon the positive findings in the phase III U.S. trial, Merck applied in February 2016 to the U.S. Food and Drug Administration for approval of the tablet as a biologic agent in patients aged 12 years or older.

HDM is the most common indoor allergen in the world. Unlike pollen and ragweed allergies, it’s not a seasonal problem. Moreover, HDM-induced allergic rhinitis is associated with increased risk of asthma. Although HDM allergic rhinitis can be treated symptomatically with oral antihistamines and nasal steroids, allergy immunotherapy has the appeal of addressing the underlying disease mechanism and potentially altering the long-term course. SLIT using a highly standardized HDM allergen extract offers a major advantage over traditional allergy immunotherapy via a lengthy program of subcutaneous injections – namely, the convenience of home self-administration.

The primary endpoint in the U.S. pivotal trial was the total combined rhinitis score (TCRS), which is the sum of the daily rhinitis symptom score and the daily rescue medication usage score averaged over the last 8 weeks of the year-long study. The FDA has set the bar for establishing clinically meaningful improvement: it requires demonstration of a reduction in the TCRS of at least 15%, compared with placebo. The 12 SQ HDM SLIT-tablet trial exceeded this standard, achieving a 17% reduction. The study also met its key prespecified secondary endpoints, including a 16% reduction in the daily rhinosinusitis symptom score and an 18% decrease in the daily medication score, compared with placebo.

Participants in the trial had a mean 18-year history of allergic rhinitis with or without conjunctivitis. Seventy-five percent of them were sensitized to other common allergens in addition to HDM, and 31% of subjects had comorbid asthma. The HDM SLIT therapy was equally effective in asthmatics and nonasthmatics, in patients allergic only to HDM and those who were polysensitized, and in subjects with and without conjunctivitis, according to Dr. Nolte.

There were no serious adverse events related to the 12 SQ HDM SLIT-tablet. A total of 9.8% of patients discontinued SLIT because of treatment-emergent adverse events, chiefly mild-to-moderate throat irritation, mouth swelling, or itchiness of the mouth or ears.

“Importantly, these events were very transient. They occurred typically within the first 8 days and lasted 14-67 hours, with a median 1-day duration of rescue medication,” he said.

Symptomatic improvement was typically seen beginning at 8-12 weeks. Adults were free to take the once-daily tablet anytime during the day. The pediatric patients were advised not to do so in the morning because they wouldn’t be under observation while on a school bus.

The tablet is based upon a formulation of allergen extracts from the two major species of HDM: Dermatophagoides pterornyssinus and D. farinae. More than 90% of HDM-sensitized patients are sensitized to both. A highly standardized manufacturing process ensures that the tablet contains 50 mcg of the four major HDM allergens in equal ratio – Der f1, Der p2, Der p1, and Der f 2 – plus other components.

In response to audience questions, Dr. Nolte said the company had tried incorporating an antihistamine into the tablet to block adverse reactions but it didn’t work. Adverse events typically occur within a couple of minutes after taking the tablet, and antihistamines are far too slow-acting to help.

“You can premedicate with antihistamines. We know European investigators and clinicians who are doing it. But I would not recommend it personally, because these tablets are taken at home after the first administration in the office, and I think it’s important that the patient has a good feel for what happens over the following days. There is a potential risk of masking side effects with premedication, which could be a concern,” Dr. Nolte said.

Merck already has two FDA-approved SLIT tablets developed with ALK on the U.S. market: Grastek, for treatment of grass pollen–induced allergic rhinitis in children and adults, and Ragwitek, for ragweed-induced allergic disease in adults.

The trial was sponsored by Merck and presented by a full-time company employee.