Drug Allergy
General drug allergy evaluation including reaction history and risk assessment.
Overview
Drug allergies are adverse reactions to medications that involve the immune system. They can range from mild skin reactions to life-threatening anaphylaxis. Accurate diagnosis is crucial to avoid unnecessary medication restrictions while ensuring patient safety. Many reported drug allergies are actually adverse drug reactions or intolerances, not true allergies.
types
ige
name
IgE-Mediated (Immediate)
timing
Occurs within minutes to 1-2 hours after exposure
symptoms
- Hives
- Swelling
- Anaphylaxis
- Bronchospasm
examples
Penicillin, cephalosporins, sulfonamides, NSAIDs
non Ige
name
Non-IgE-Mediated (Delayed)
timing
Occurs hours to days after exposure
symptoms
- Maculopapular rash
- Drug reaction with eosinophilia and systemic symptoms (DRESS)
- Stevens-Johnson syndrome
- Toxic epidermal necrolysis
examples
Anticonvulsants, allopurinol, sulfonamides
pseudoallergy
name
Pseudoallergic Reactions
mechanism
Non-immune mediated reactions that mimic allergic reactions
examples
Radiocontrast media reactions, NSAID-induced urticaria/angioedema
note
Not true allergies but can be severe
common Culprits
antibiotics
- Penicillin and related drugs
- Cephalosporins
- Sulfonamides
- Vancomycin
nsaids
Aspirin, ibuprofen, naproxen - can cause urticaria, angioedema, or anaphylaxis
contrast
Radiocontrast media - can cause anaphylactoid reactions
chemotherapy
Various agents can cause hypersensitivity reactions
biologics
Monoclonal antibodies, vaccines - can cause infusion reactions
evaluation
history
- Detailed reaction history - timing, symptoms, severity
- Medication name, dose, route of administration
- Previous exposures and reactions
- Concurrent medications
- Underlying medical conditions
- Family history of drug allergies
- Documentation in medical records
risk Stratification
high Risk
- Severe reactions (anaphylaxis, SJS, TEN, DRESS)
- Recent reaction (< 5 years)
- Multiple drug allergies
- Reaction to structurally similar drugs
low Risk
- Mild, remote reactions (> 10 years ago)
- Unclear reaction history
- Symptoms consistent with side effects rather than allergy
- No reaction on recent exposure
testing
skin
- Skin prick testing for IgE-mediated reactions
- Intradermal testing
- Patch testing for delayed reactions
- Limited availability for most drugs
ige
Serum-specific IgE testing available for some drugs (penicillin, some cephalosporins)
challenge
- Graded drug challenge (test dose) - for low-risk patients
- Drug desensitization - for high-risk patients who need the drug
- Must be performed in controlled setting with emergency equipment
note
Most drug allergies are diagnosed clinically based on history
management
avoidance
- Avoid the culprit drug and structurally similar drugs
- Document clearly in medical records
- Patient education about drug names and alternatives
- Medical alert bracelet for severe allergies
alternatives
- Identify safe alternative medications
- Consider cross-reactivity patterns
- Consult with allergist or pharmacist
delabeling
indication
When allergy is unlikely or low-risk, consider delabeling to expand treatment options
process
- Comprehensive history review
- Risk assessment
- Testing if available
- Graded challenge if appropriate
- Document removal of allergy label if challenge is negative
benefits
- Expands treatment options
- Reduces unnecessary antibiotic restrictions
- Improves patient outcomes
- Reduces healthcare costs
desensitization
indication
For patients with confirmed allergy who require the drug
process
Gradually increasing doses under medical supervision
setting
Must be performed in hospital or clinic with emergency equipment
duration
Temporary - patient must continue taking drug regularly to maintain tolerance
penicillin
overview
Penicillin allergy is the most commonly reported drug allergy, but up to 90% of patients are not truly allergic
cross Reactivity
cephalosporins
Low cross-reactivity (< 2%) with modern cephalosporins
carbapenems
Low cross-reactivity
monobactams
No cross-reactivity (aztreonam is safe)
evaluation
Skin testing and challenge protocols available for penicillin allergy evaluation
referral
Refer to allergist for penicillin allergy evaluation and delabeling
documentation
importance
Accurate documentation prevents future medication errors
elements
- Drug name and class
- Reaction description and timing
- Severity
- Treatment required
- Date of reaction
- Testing results if available
when To Refer
- Unclear diagnosis or reaction history
- Need for drug that patient reports allergy to
- Multiple drug allergies limiting treatment options
- Severe reactions requiring specialized evaluation
- Penicillin allergy evaluation and delabeling
- Drug desensitization needed
- Complex cross-reactivity questions
prognosis
Many drug allergies can be safely delabeled through proper evaluation, expanding treatment options for patients. For confirmed allergies, strict avoidance and identification of safe alternatives is essential. Drug desensitization can allow use of necessary medications in allergic patients when performed under appropriate medical supervision.
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