A Shot in the Arm for Allergies

Allergen immunotherapy is the practice of injecting (subcutaneously) small quantities of allergens (such as pollens, molds) to patients who are allergic to those allergens.  Increasing amounts of these allergens are injected over a period of time.  It is theorized that some patients slowly begin to tolerate higher amounts of allergens and eventually, if successful, symptoms to the allergens are minimal when these patients are exposed to the allergens in their environment.  

Allergen immunotherapy was first practiced in 1911 in England when grass pollen extract was injected into a person whose allergic symptoms coincided with the season when grass pollinated. Since then, controlled studies have shown that many patients have effectively reduced symptoms of allergic rhinitis, allergic conjunctivitis, allergic asthma and allergies to some stinging insects.

Standardized allergens available for injection in the USA include: cat dander, grass pollens, dust mites, and short ragweed. By “standardized”, one refers to a reagent that has a defined potency and is labeled with a common unit. Un-standardized vaccines vary in biologic activity between manufacturers and lot numbers. Even if the protein content is standard in these, the allergic potency of the protein is not. 

The dosage schedule (i.e., how much one increases or decreases the dose from the previous injection) varies for a number of circumstances. For example, if the interval between a patient’s injections is excessively long, the dose of the vaccine cannot be increased and, in fact, it must often be reduced. For this reason, there must be communication between prescribing allergists and the physicians who administer the vaccine.

Precautions must always be taken to prepare for a systemic reaction to the vaccine (this includes a tourniquet above injection site and epinephrine). Precautions must be taken for large local reactions (this includes: oral steroids, non-steroidal anti-inflammatory drugs, and oral antihistamines).

After one year of immunotherapy, the clinical improvement  experienced by the allergic patient must be reassessed.  By then, improvement should be apparent. If improvement occurred, then immunotherapy is often continued for 3 to 5 years

(Huggins JL, Looney RJ. Am Fam Physician 2004; 70:689-696.) —H. T.