Allergy shots, or Subcutaneous Immunotherapy (SCIT), are a medical treatment designed to modify the body’s long-term response to substances that trigger allergic reactions. This therapeutic approach involves administering gradually increasing doses of a specific allergen extract over time. The primary function of SCIT is to desensitize the immune system, reprogramming it to stop viewing the harmless substance as a threat. By altering the immune response, allergy shots offer a long-term treatment option for conditions like allergic rhinitis, allergic asthma, and insect venom hypersensitivity.
The Active Allergen Extracts
The core ingredient in every allergy shot mixture is the active allergen extract, which is the biological material responsible for causing the patient’s symptoms. These extracts are liquid solutions containing dissolved allergenic proteins sourced from the environment. The specific components chosen for the treatment vials are highly individualized and based on a comprehensive allergy evaluation, such as skin or blood testing, to confirm the patient’s sensitivities.
Allergens used in the extracts are diverse, covering common triggers such as pollens from weeds, grasses, and trees, as well as fungal mold spores. Other source materials include dust mites, animal dander, and the venom from stinging insects. Manufacturers obtain these raw materials and subject them to extraction and purification steps to create a concentrated stock solution.
The selection process ensures that the chosen extracts are clinically relevant, meaning they are present in the patient’s local environment and confirmed to cause their symptoms. The final product is a complex mixture of allergenic proteins, considered a crude extract rather than a single, isolated protein. The goal is to provide the immune system with the full profile of the trigger it encounters naturally.
The Carrier and Stabilizing Agents
Beyond the active allergen, the treatment mixture contains several inactive components that serve to stabilize the extract, ensure sterility, and control the release of the allergen into the body. The most common liquid base is a sterile diluent, frequently a phenol-saline solution. Sodium chloride is included to maintain isotonicity, while sodium bicarbonate acts as a buffering agent to stabilize the pH.
To prevent bacterial growth and maintain the shelf life of the mixture, a preservative is necessary, with phenol commonly used for its antimicrobial properties. Glycerin is another additive, functioning as both a preservative and a stabilizer. Glycerin helps preserve the potency of the extract and gives it a slightly thicker consistency, which can influence how quickly the solution is absorbed after injection.
In some formulations, the allergen proteins are combined with aluminum salts, often referred to as alum-precipitated extracts. Aluminum hydroxide acts as an adjuvant, which slows the rate at which the allergen is released from the injection site. This controlled, slow absorption allows for larger doses to be safely administered at less frequent intervals, leading to a more rapid progression to the therapeutic maintenance dose.
Customizing the Treatment Mixture
The final treatment mixture is a highly individualized product, created by combining standardized extracts with the appropriate diluents in specific proportions for each patient. Standardization ensures consistency of allergen content across different batches and manufacturers. Potency is often measured in units like Bioequivalent Allergy Units (BAU) or Protein Nitrogen Units (PNU). The allergist uses these measurements to calculate the exact concentration required for the patient’s treatment plan.
Immunotherapy treatment is divided into two distinct phases, beginning with the “build-up” phase. This involves a series of injections with gradually increasing concentrations of the allergen, typically lasting three to six months. Injections are administered frequently, often one to three times per week, allowing the body to slowly adapt to the foreign substances. The goal is to reach the maximum tolerated dose, known as the maintenance dose.
Once the maintenance dose is reached, the patient transitions to the “maintenance” phase. The concentration remains stable, but the frequency of injections is reduced, usually to once every two to four weeks. The entire treatment plan, which can last three to five years, is continuously adjusted based on the patient’s individual tolerance and any reactions they experience.