Penicillin Allergy: Symptoms, Testing, and What to Do

~10% of people report penicillin allergy, but >90% test negative. True IgE-mediated allergy is less common than believed.

Testing Methods

1. Skin testing (gold standard): Prick then intradermal with penicilloyl-polylysine (PPL) and penicillin G. Negative predictive value >99%.
2. Serum specific IgE: Less sensitive than skin test; used if skin testing unavailable/contraindicated.
3. Graded oral challenge: Under observation, after negative skin test. Confirms tolerance.
4. History alone: Insufficient; many "allergies" are side effects (GI upset) or viral rashes misattributed.

True Allergy Symptoms (IgE-mediated)

• Urticaria, angioedema, wheezing, anaphylaxis (usually within 1 hour).
• Delayed reactions (serum sickness, DRESS, SJS/TEN) are T-cell mediated, not IgE.

Action Steps

• Report any reaction to your provider.
• Request allergy evaluation—delabeling allows safer, cheaper, narrower-spectrum antibiotics.
• If truly allergic: avoid penicillins; cephalosporins often tolerated (cross-reactivity ~1–2%).