Allergy Drops: Not Yet Ready

For many years allergists have been searching for alternatives to allergy shots that successfully desensitize patients to the substances to which they are allergic. While allergy shots are very effective, the fear of injections deters some patients from undergoing the therapy.

Recent research in Europe shows that oral allergy drops can desensitize patients to certain allergens, including tree and grass pollens. This treatment is called sublingual immunotherapy (SLIT) because the drops are put under the tongue. Increasing concentrations of these drops are given to patients until they develop tolerance to the allergens.

The SLIT approach, developed in Europe, is different than the ineffective allergy drops used by some Otolaryngology (Ear, Nose and Throat) allergists in previous decades in that the doses used in Europe are much higher.

While there is much interest in SLIT in the U.S., several road blocks to its use exist here.

First, the pattern of allergies is different in the U.S. and Europe. Americans tend to be allergic to multiple major allergens, including several pollens (like trees, grasses, and ragweed), molds, dust mites and pet danders. Europeans, however, are more likely to be sensitized to only one or two allergens, for example birch tree pollen in Scandanavia or grass pollen in England.

Most of the SLIT studies involve only one allergen. It is not known how well the SLIT approach will work for polysensitized patients, which is the norm in the U.S.

Second, the allergy drops used for SLIT have not been standardized. The studies have used different materials from various pharmaceutical manufacturers; discrepancies exist between companies as to the composition and concentrations of the drops. Similarly, the starting and maintenance doses of the drops have not been established, and they seem to vary with the manufacturer.

Third, while the safety profile for SLIT appears to be favorable, the types of adverse reactions are not well understood. Because the drops are taken by mouth, there is a greater risk of gastrointestinal side effects such as diarrhea. As with allergy shots, there also is a small risk of serious anaphylactic reactions with SLIT.

Fourth, not enough comparative studies between SLI T and traditional allergy shots have been done to determine which approach is more effective, both as to clinical results and cost.

The costs of materials for SLIT are higher than for shots. For SLIT to be effective, high concentrations of allergens are needed in the drops, requiring more of expensive allergen extracts. SLIT, however, does not require the costs of syringes or injections.

Finally, from a practical point of view, the U.S. Food and Drug Administration has not yet approved any allergy drops for use in the United States. There are some studies underway to seek approval of such drops, but allergists using them are doing so on a research basis. It may be some time before this alternative to allergy shots is available on a routine basis.