One of my patients with a significant history of allergies who had been repeatedly late for her weekly allergy shot asked me the other day in clinic whether we also offered sublingual immunotherapy or SLIT, the liquid allergy drops patients place under their tongue and then swallow. More and more allergy and ENT practices are making this alternate form of allergy immunotherapy available. Unfortunately, the FDA has not yet approved SLIT for use in the United States, although this method of allergy desensitization is commonly being used in Europe. Some doctors in the United States have been using the same allergy extract regularly approved for injections for sublingual treatments, although the doses administered sublingually are much higher.
And here lies the rub. Current studies on SLIT, most done in Europe, don’t delineate the precise, effective dose necessary for treatment success. In the U.S., such doses are regularly agreed upon for our much more commonly prescribed allergy shots. Further, most SLIT studies in Europe focus on patients who are mono-sensitized or allergic to only one allergen. Here in the U.S., patients are largely multi-sensitized or allergic to multiple different allergens. Most of our allergy shot patients are therefore prescribed allergy extract that consists of many different allergens, such as cat, dog, dust mite, tree, grass, mold and weed—not just grass extract alone, for example. We’re not sure yet whether mixing many different allergens together for SLIT would be as effective in treating multi-sensitized patients as one sublingual extract is in treating patients only allergic to one allergen. The one SLIT study done so far in the United States that looked at treating patients with multiple allergies revealed that mixing the allergens together blunted their efficacy.
Nonetheless, SLIT will likely become a commonly prescribed allergy treatment in the future. Like allergy shots, SLIT has been shown to be effective for treating allergic asthma and nasal and ocular allergies. Unlike allergy shots, SLIT can be administered at home and has a low risk for anaphylaxis, although serious allergic reactions have occurred. Recent evidence has even shown that both shots and sublingual drops might also help treat allergic patients with eczema or atopic dermatitis. As with allergy shots, SLIT has been shown to have long-lasting benefits, remaining effective years after patients have stopped the drops. Again, these promising results apply to mono-sensitized patients treated with allergic extract containing only one type of allergen and not necessarily to the multi-sensitized patient who predominates in the U.S.
Future SLIT studies will hopefully reveal how doctors can appropriately dose and mix relevant allergens to achieve the best treatment outcomes. Until that information is known, patients should understand that SLIT for patients with multiple allergies is in an investigational stage. Because SLIT is not FDA-approved it is not currently covered by insurance. Therefore doctors who provide this therapy do so off-label and so often charge cash. For all these reasons, the Atlanta Allergy & Asthma Clinic does not yet offer SLIT. As more information becomes available we may change our views, but for now, we prefer the tried and true.