SLIT Treatment for Allergic Rhinitis Nothing to Sneeze About

This article has been reviewed by Thanai Pongdee, MD, FAAAAI

Allergic rhinitis, sometimes referred to as hay fever, is an inflammatory disease that causes sneezing, itchy/watery eyes, itchy/runny nose and congestion. For millions of sufferers, antihistamines and nasal corticosteroid medications provide temporary relief of symptoms. For others, allergy shots (subcutaneous immunotherapy or SCIT) are a long-term treatment alternative.

Allergy shots involve frequent injections of increasing amounts of allergen extract. They can be effective at controlling symptoms of allergic rhinitis, but the injection schedule can be difficult to maintain, local reactions to the injections are common, and severe allergic reactions and even deaths have been reported.

Another form of therapy is currently being investigated in clinical research settings for use in the United States. Sublingual Immunotherapy (SLIT) involves a dosing schedule of increasing amounts of allergen, much like the shots. However, rather than shots, the allergens are administered in a liquid or tablet form under the tongue. SLIT is currently being used in Europe and some countries in South America. Based on reviews of research projects done both here in the US and overseas, SLIT has the potential to be a safe and effective treatment for allergic rhinitis.

SLIT appears to have a favorable safety profile. In one review of the literature, the authors estimated that in approximately 1.2 million doses administered to 4400 patients, there were no serious, "life-threatening reactions". There are reports of anaphylaxis with SLIT, but the incidence is rare. The primary symptoms reported by subjects receiving SLIT included mild "local" itching/burning of the mouth or lips, increase in rhinitis symptoms, gastrointestinal symptoms, and rarely, an increase in asthma symptoms. The reactions reported by subjects receiving SLIT were only significant enough to make the subject stop taking SLIT in less than 5% of the cases. SLIT has been studied in children as young as a year old. The primary symptoms reported by parents were oral itching, itchy skin, abdominal pain, and nausea and vomiting.

The effectiveness of SLIT has been studied in both adults and children. There have been over 60 controlled clinical trials published since1986 with the majority of studies being done in dust mite or grass allergic individuals. In general, most studies demonstrated that SLIT is safe and effective.  However, some of these studies have demonstrated no efficacy. The variation in effectiveness had been attributed to the differences in the dose of allergen used for the various studies. In general, the higher doses of allergen appeared to have the largest impact on symptom improvement.

SLIT has potential to become a useful treatment of allergic rhinitis and asthma. Although several clinical trials with sublingual immunotherapy have been conducted in the United States there are currently no FDA-approved formulations for sublingual immunotherapy. SLIT is prescribed by a small percentage of US allergist, primarily using the licensed allergen extracts used for subcutaneous immunotherapy. Several questions need to be answered before SLIT is routinely used in the US. Although the optimal starting dose and dosing frequency for maintenance has been  established for some allergens, (e.g., grass), these questions have not been answered for many other  allergen (e.g., ragweed). It's not clear if the starting/maintenance doses will be the same for all of the various allergens. Once the dosing questions have been addressed, the cost-effectiveness of SLIT needs to be established.

References
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AAAAI - American Academy of Allergy Asthma & Immunology