Overview
Definition:
Allergen immunotherapy (AIT) is a treatment that involves giving gradually increasing doses of the allergen to which a patient is allergic
The goal is to increase tolerance to that allergen, thereby reducing or eliminating allergic symptoms upon natural exposure
It is typically administered via subcutaneous (SCIT) or sublingual (SLIT) routes
In pediatrics, AIT is a crucial tool for managing persistent allergic rhinitis, allergic asthma, and certain venom allergies.
Epidemiology:
Allergic diseases are highly prevalent in children, with allergic rhinitis affecting up to 40% and asthma up to 10%
A significant proportion of these children may not achieve adequate symptom control with pharmacotherapy alone, making them candidates for AIT
The decision to initiate AIT is based on symptom severity, impact on quality of life, and response to conventional treatments
The global incidence of severe AIT reactions, particularly anaphylaxis, is low but requires diligent monitoring and preparedness.
Clinical Significance:
Allergen immunotherapy offers the potential for long-term remission of allergic symptoms and a reduced risk of developing new allergies or asthma (the "atopic march")
However, it carries inherent risks, including local and systemic reactions, with the most severe being anaphylaxis
Proper patient selection, meticulous administration protocols, and robust anaphylaxis preparedness are paramount for safe and effective AIT in pediatric patients, making this a high-yield topic for DNB and NEET SS examinations.
Immunotherapy Types And Indications
Scit:
Subcutaneous immunotherapy (SCIT) involves injecting increasing doses of allergen extracts subcutaneously
Indications include allergic rhinitis/conjunctivitis, allergic asthma, and venom immunotherapy in children with confirmed IgE-mediated hypersensitivity and significant symptoms refractory to pharmacotherapy.
Slit:
Sublingual immunotherapy (SLIT) involves placing allergen extracts under the tongue
SLIT is generally considered to have a lower risk of systemic reactions compared to SCIT and is an alternative for patients who cannot tolerate SCIT or have contraindications
Indications are similar to SCIT for rhinitis and asthma.
Specific Allergens:
Commonly treated allergens in children include pollens (grass, tree, weed), dust mites, animal dander (cat, dog), and insect venoms (bee, wasp)
Food immunotherapy is a rapidly evolving area but is typically reserved for specific high-risk situations and conducted under strict supervision.
Contraindications:
Absolute contraindications include uncontrolled asthma, beta-blocker therapy, significant comorbidities, and severe immunodeficiency
Relative contraindications may include certain autoimmune diseases, severe cardiovascular disease, and pregnancy (though less relevant in pediatrics).
Risks And Adverse Reactions
Local Reactions:
Common and generally mild
Include pruritus, erythema, edema, and urticaria at the injection site for SCIT
For SLIT, oral pruritus, edema, or mild gastrointestinal upset may occur
These are usually managed by dose adjustment or temporary discontinuation.
Systemic Reactions:
Less common than local reactions, but can be more severe
Symptoms may include generalized urticaria, angioedema, rhinorrhea, conjunctivitis, wheezing, gastrointestinal symptoms (nausea, vomiting, abdominal pain), or hypotension
Prompt recognition and management are crucial.
Anaphylaxis:
The most severe, life-threatening systemic reaction
Characterized by rapid onset of symptoms involving multiple organ systems, including cardiovascular collapse, bronchospasm, angioedema, and gastrointestinal distress
Can occur minutes to hours after allergen administration, with the highest risk typically within 30 minutes post-injection for SCIT.
Delayed Reactions:
Rare, but can include serum sickness-like reactions occurring days to weeks after AIT, presenting with fever, rash, and arthralgia.
Anaphylaxis Preparedness
Pre Treatment Assessment:
Thorough history of allergies, previous reactions, current medications (especially beta-blockers), and comorbidities
Ensure patient and caregivers are educated about potential symptoms and what to do.
Administration Protocols:
SCIT: Administer injections in a clinical setting with direct medical supervision for at least 30 minutes post-injection
SLIT: Patients should hold the SLIT tablet/drops under the tongue for the prescribed duration (usually 1-2 minutes) and then swallow, avoiding eating or drinking for 5 minutes
Patients should remain in the clinic for at least 30 minutes after the first few doses of SLIT and if dose adjustments are made.
Emergency Equipment:
Readily accessible epinephrine auto-injectors (multiple sizes appropriate for pediatric weight), oxygen, airway adjuncts, intravenous fluids, antihistamines, and corticosteroids
All staff administering AIT must be trained in their use.
Emergency Response Plan:
Clear, documented plan for managing anaphylaxis, including immediate administration of epinephrine, calling for emergency medical services, and monitoring the patient until symptoms resolve and they are stable
Regular drills and staff training are essential.
Management Of Adverse Reactions
Local Reactions:
For SCIT, ice application and oral antihistamines
For SLIT, oral antihistamines may suffice
Dose reduction or interruption of therapy may be necessary if reactions are persistent or severe.
Systemic Reactions:
Immediate cessation of immunotherapy
Administration of intramuscular epinephrine is the cornerstone of treatment
Oral antihistamines and corticosteroids can be used as adjuncts
Close monitoring for recurrence is vital.
Anaphylaxis Management:
First-line treatment is intramuscular epinephrine (0.01 mg/kg, max 0.3-0.5 mg, repeated every 5-15 minutes as needed)
Secure airway if compromised
Administer oxygen
IV fluids for hypotension
Antihistamines and corticosteroids are second-line and do not replace epinephrine
Hospitalization for observation is mandatory
Identification and avoidance of the triggering allergen are crucial.
Dose Escalation Strategy:
Modified rush or conventional build-up schedules should be used cautiously in pediatrics, with careful monitoring
Any significant reaction should prompt a review of the build-up schedule and potentially a reduction in dose or slower escalation.
Key Points
Exam Focus:
Understand the mechanism of AIT, indications for SCIT vs
SLIT in pediatrics, and contraindications
Be prepared to recognize and manage local reactions, systemic reactions, and anaphylaxis with specific pediatric dosages of epinephrine.
Clinical Pearls:
Always administer SCIT in a monitored setting for at least 30 minutes
Educate parents/guardians thoroughly on signs of reaction and when to seek immediate medical help
Have age- and weight-appropriate epinephrine auto-injectors readily available for all AIT administration sites.
Common Mistakes:
Failure to adequately screen patients for contraindications
Inadequate observation period post-administration
Delay in epinephrine administration during anaphylaxis
Over-reliance on antihistamines as primary treatment for anaphylaxis
Incomplete patient/caregiver education regarding risks.