What are the symptoms of an allergic reaction to immunotherapy (allergy shots)?

From the Guidelines

Allergy shots can cause various symptoms, including local reactions such as redness, swelling, and itching at the injection site, as well as more serious systemic reactions like hives, sneezing, and anaphylaxis, and it is essential to remain at the doctor's office for 30 minutes after receiving an allergy shot to monitor for serious reactions 1. Allergy shots, or immunotherapy, work by gradually exposing your immune system to allergens, causing it to build tolerance over time, but this process can initially trigger allergic symptoms. Common symptoms include:

• Redness, swelling, and itching at the injection site, which typically resolve within a few hours
• More significant local reactions with larger areas of swelling that can last 1-2 days
• Systemic reactions, which are less common but more serious, including:
  • Hives
  • Sneezing
  • Nasal congestion
  • Throat tightness
  • Wheezing
  • Rarely, anaphylaxis If you experience mild local reactions, applying ice to the area and taking an antihistamine like Benadryl (25-50mg) or Zyrtec (10mg) can help 1. For more severe reactions, your allergist may recommend taking an antihistamine before your shots. It is crucial to assess the patient's current health status before administration of the allergy immunotherapy injection to determine whether there were any health changes that might require modifying or withholding that patient's immunotherapy treatment, and poorly controlled asthma has been identified as a risk factor for a severe immunotherapy-induced reaction 1. Always remain at the doctor's office for 30 minutes after receiving an allergy shot to monitor for serious reactions, and if you experience symptoms like difficulty breathing, severe hives, or dizziness, alert the medical staff immediately as epinephrine (EpiPen) may be needed 1.

From the FDA Drug Label

These symptoms occur in some persons receiving therapeutic doses of epinephrine, but are more likely to occur in patients with heart disease, hypertension, or hyperthyroidism [see Warnings and Precautions 5-(5. 3)]. Adverse reactions reported in observational trials, case reports, and studies are listed below by body system: Cardiovascular: angina, arrhythmias, hypertension, pallor, palpitations, tachyarrhythmia, tachycardia, vasoconstriction, ventricular ectopy and stress cardiomyopathy. Respiratory: respiratory difficulties. Neurological: dizziness , disorientation , excitability , headache , impaired memory , lightheadedness , nervousness , panic, psychomotor agitation, sleepiness , tingling , tremor, and weakness. Psychiatric: anxiety, apprehensiveness, restlessness. Gastrointestinal: nausea, vomiting Other: Patients with Parkinson's disease may experience psychomotor agitation or a temporary worsening of symptoms [see Warnings and Precautions 5-(5.3)]. Diabetic patients may experience transient increases in blood sugar [see Warnings and Precautions 5-(5. 3)]. Accidental injection into the digits, hands or feet may result in loss of blood flow to the affected area [see Warnings and Precautions 5-(5. 1)]. Adverse events experienced as a result of an injection into these areas include increased heart rate, local reactions including injection site pallor, coldness, hypoesthesia, and tissue loss, or injury at the injection site resulting in bruising, bleeding, discoloration, erythema, and skeletal injury Injection into the buttock has resulted in cases of gas gangrene [see Warnings and Precautions 5-(5.1)]. Rare cases of serious skin and soft tissue infections, including necrotizing fasciitis and myonecrosis caused by Clostridia (gas gangrene), have been reported following epinephrine injection in the thigh [see Warnings and Precautions 5-(5. 2)]. Skin: sweating.

The symptoms of an allergy shot using epinephrine (IM) may include:

• Cardiovascular symptoms: angina, arrhythmias, hypertension, pallor, palpitations, tachyarrhythmia, tachycardia, vasoconstriction, ventricular ectopy, and stress cardiomyopathy.
• Respiratory symptoms: respiratory difficulties.
• Neurological symptoms: dizziness, disorientation, excitability, headache, impaired memory, lightheadedness, nervousness, panic, psychomotor agitation, sleepiness, tingling, tremor, and weakness.
• Psychiatric symptoms: anxiety, apprehensiveness, restlessness.
• Gastrointestinal symptoms: nausea, vomiting.
• Other symptoms: increased heart rate, local reactions, injection site pallor, coldness, hypoesthesia, tissue loss, bruising, bleeding, discoloration, erythema, skeletal injury, and sweating. 2

From the Research

Allergy Shot Symptoms

• Local reactions (LR) to subcutaneous immunotherapy (SCIT) are common, occurring in 26-86% of patients 3
• Symptoms of local reactions may include redness, swelling, and itching at the injection site
• Systemic reactions, such as anaphylaxis, can also occur, although they are less common 4

Management of Allergy Shot Symptoms

• Epinephrine is the first-line treatment for anaphylaxis, and its early use can reduce the risk of uncontrolled reactions and hospital admission 4
• Antihistamines, such as diphenhydramine, may also be effective in reducing local reactions to SCIT 3
• Corticosteroids are not typically recommended for the treatment of anaphylaxis, and their use may actually increase the risk of hospital admission 4

Prevention of Allergy Shot Symptoms

• Pre-rinsing SCIT syringes with epinephrine or antihistamines may help reduce the risk of local reactions 3
• Pretreatment with oral antihistamines may also help reduce the risk of local reactions, although it may not be effective in all patients 3
• Allergen immunotherapy is generally well-tolerated, but patients should be closely monitored for signs of systemic reactions or other adverse effects 5