Author: Agnes LEUNG
Assistant Professor, Department of Paediatrics, CUHK
In the previous articles of the series, we have discussed how severe and life-threatening food allergy can be. A “fight-and-flight” approach have been the current mainstay of management – “fighting” against the allergic reactions with emergency medications such as antihistamines and adrenaline autoinjectors; and “fleeing” from the reactions by avoiding the offending foods. What else can be done to protect the patients from unpredictable food allergic reactions? Is it possible for them to acquire tolerance to the allergens?
In recent years, extensive studies have been undertaken to explore a variety of novel treatments for food allergies. Among all types of novel treatments, oral immunotherapy (OIT) has been evaluated to the greatest extent on its efficacy and safety. OIT requires patients to regularly expose to one or multiple food allergens via oral ingestion under medical supervision. The goal to gradually and safely increase the individual’s tolerance to the food, with the hope that they will eventually be able to consume a normal-sized portion of the allergenic food without experiencing symptoms. OIT has shown promise in treating food allergies, particularly peanut allergy. Multiple clinical trials have shown that OIT can be effective in desensitizing individuals with peanut allergy, with doses of up to 4g of peanuts eventually tolerated, and a reduced risk of severe reactions over time. A smaller number of studies have evaluated OIT for other food allergies, such as cow’s milk and egg, and have also shown benefits for some individuals. Currently, efficacy of OIT for wheat, fish and shrimp allergies are being studied locally. In a landmark trial, 96% and 63% of peanut-allergic patients who received one-year of a FDA-proven OIT (Palforzia®) were able to tolerate 300 mg of peanut protein (about 1¼ peanut kernel) and 1000 mg of peanut protein (about 4 peanut kernels) with mild symptoms respectively – compared to 8% and 2% of patients who received placebo.
OIT typically consists of three stages. The first stage is an initial dose escalation, during which the patient will receive increasing amount of the allergenic food (containing a few micrograms to milligrams of food protein) over hours or days. This will be followed by the build-up phase, where the patient will gradually increase the daily dose of allergen over several months if tolerated. Finally, they will reach the maintenance phase and consume the same amount of treatment food every day (containing up to a few grams of food protein). The optimal duration of OIT for food allergies is not yet known, but most studies suggest that benefits might be maintained if the treatment is continued for at least 12-24 months.
Diagnostic tests such as blood specific IgE test, skin prick test and oral food challenge are often done before the commencement of treatment. This is to confirm the diagnosis of an IgE-mediated food allergy in the patients and therefore make sure they are in actual need of the treatment. The tests will often be repeated upon completion of OIT to evaluate the treatment outcomes. The main treatment outcomes are to induce desensitisation or sustained unresponsiveness – desensitisation refers to an increase in the threshold amount of food to trigger an allergic reaction without experiencing allergic symptom, but it requires regular allergen exposure. In contrast, sustained unresponsiveness, is the state when patients no longer develop reactions upon allergen exposure even though the treatment has been withdrawn for a minimum of 6 to 8 weeks. It is thought to reflect re-programming of the immune system from an allergic to tolerance state. Patients can therefore benefit from a better quality of life with lower chance of severe allergic reactions in the events of accidental exposure to allergen or cross-contamination of food. Those who have achieved sustained unresponsiveness can even freely integrate the allergen into their diet, removing the burden of dietary restriction.
However, side effects are common with OIT, which include oral and throat itchiness, swelling, hives, tummy pain and vomiting. Sometimes, severe side effects such as trouble breathing and wheezing occur. As such, OIT is typically only performed by allergists or other trained medical professionals in specialized clinical settings and may not be suitable for all individuals with food allergies. In other studies, the safety profile of OIT improves when probiotics are being incorporated into the OIT treatment. Other forms of immunotherapy for food allergy are also being investigated, such as epicutaneous immunotherapy (EPIT) and biologicals, which may offer a more convenient and potentially safer alternative to OIT in the future. Before the start of treatment, the patients, parents and caregivers should be educated on how to recognize allergy symptoms and how to manage them. They should also be informed on the usage of adrenaline autoinjectors and provided an anaphylaxis action plan in order to be prepared for any adverse events induced by the OIT.