Allergen immunotherapy
Allergen immunotherapy, also known as desensitization or hypo-sensitization, is a medical treatment for environmental allergies and asthma. Immunotherapy involves exposing people to increasing amounts of allergens in an attempt to change the immune system's response.
Meta-analyses have found that injections of allergens under the skin are effective in the treatment of allergic rhinitis in children and in asthma. The benefits may last for years after treatment is stopped. It is generally safe and effective for allergic rhinitis, allergic conjunctivitis, allergic forms of asthma, and stinging insects. The evidence also supports the use of sublingual immunotherapy against rhinitis and asthma, but it is less strong. In this form the allergen is given under the tongue and people often prefer it to injections. Immunotherapy is not recommended as a stand-alone treatment for asthma.
Side effects during sublingual immunotherapy treatment are usually local and mild and can often be eliminated by adjusting the dosage. Anaphylaxis during sublingual immunotherapy treatment has occurred on rare occasions.
Potential side effects related to subcutaneous immunotherapy treatment for asthma and allergic rhinoconjunctivitis include mild or moderate skin or respiratory reactions. Severe side effects such as anaphylaxis during subcutaneous immunotherapy treatment are relatively uncommon.
Discovered by Leonard Noon and John Freeman in 1911, allergen immunotherapy is the only medicine known to tackle not only the symptoms but also the causes of respiratory allergies. A detailed diagnosis is necessary to identify the allergens involved.
Methods of desensitization
Subcutaneous
Subcutaneous immunotherapy, also known as allergy shots, is the historical route of administration and consists of injections of allergen extract, which must be performed by a medical professional. Subcutaneous immunotherapy protocols generally involve weekly injections during a build-up phase, followed by a monthly maintenance phase that consists of injections for a period of 3–5 years. The build-up phase involves the patient being administered injections which contain increasing amounts of allergens about one to two times per week. The length of the build-up phase is dependent upon how often injections are administered, but normally ranges from three to six months. After the effective dose is reached, the maintenance phase is implemented, which varies depending upon an individual's response to the build-up phase.SCIT can be used for desensitizations to airborne allergens and insect venoms. Common airborne allergens targeted in SCIT include pollens, animal danders, molds, and cockroach allergens. Venoms from bees and wasps are often the target of SCIT in patients with severe insect venom allergies.
When accounting for a person's age, type of allergen, and severity of allergy, there is a high probability that subcutaneous allergen immunotherapy may provide greater clinical and immunological responses than sublingual allergen immunotherapy. Compared to sublingual allergen immunotherapy, there are no significant differences observed in quality of life.
It is possible, but rare, that people undergoing subcutaneous allergen immunotherapy may experience a fatal anaphylactic event. Subcutaneous allergen immunotherapy adverse events vary significantly depending on different allergenic extracts and the application of different allergen immunotherapy schedules.
Allergen immunotherapy schedules include the "cluster" approach, which involves administering several doses sequentially in a single day; a "conventional" approach, which involves incrementally increasing the dose over approximately 15 weeks; and the "rush" approach, which involves administering incremental doses at intervals of 15–60 minutes over 1–3 days.
It is challenging to perform an adequate risk assessment on the use of subcutaneous allergen immunotherapy compared to other forms of allergen immunotherapy administration due to the variability of immunotherapy schedules and further research is required.
Sublingual
immunotherapy involves putting drops or a tablet of allergen extracts under the tongue, which are then absorbed through the lining of the mouth. Sublingual immunotherapy has been demonstrated to be effective against rhinoconjunctivitis and asthma symptoms. This effectiveness, however, varies depending on the type of allergen. The strongest evidence for the efficacy of sublingual immunotherapy comes from studies that used grass allergens or mite allergens to alleviate allergic rhinitis symptoms; the evidence shows modest improvement.Sublingual immunotherapy is used to treat allergic rhinitis, often from seasonal allergies, and is typically given in several doses over a 12-week period. It works best when given 12 weeks before the start of the pollen season. The first dose is given by a physician to monitor for any rare reactions or anaphylaxis. Subsequent doses can be taken at home which makes this a convenient alternative to subcutaneous immunotherapy.
While a number of side effects have been associated with sublingual immunotherapy, serious adverse effects are very rare, and there has not been a reported fatality. There have been a small number of reports of anaphylaxis. The majority of side effects are 'local' and usually resolve within a few days. They include swelling of the mouth, tongue or lip, throat irritation, nausea, abdominal pain, vomiting, diarrhea, heartburn, and uvular edema. It is not yet clear if there are any risk factors that might increase a person's susceptibility to these adverse effects. Sublingual immunotherapy appears to be better tolerated than subcutaneous immunotherapy and causes fewer side effects. The safety of sublingual immunotherapy has not been studied extensively in people with chronic immunodeficiency or autoimmune disorders.