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Delayed urticaria and angioedema to amoxicillin after negative testing for penicillin

Question:

4/7/2017
Patient presented with urticaria onset seven days after completing amoxicillin treatment. Of note, she has history of recurrent spontaneous hives. I performed skin test with prepen and pen G, skin prick and intradermal as recommended. I also performed prick testing with amoxicillin oral suspension 125 mg/5ml, all negative. Oral challenge with 500 mg of amoxicillin followed and observed in the office for two hours. She only complained of itching of face and back prior to discharge but no rashes were noted. Seventeen hours after the provocation, she woke up with urticaria and lip angioedema. Are there reports of delayed IgE reactions after provocation. Could this be her CIU, should I consider re-challenge?

Answer:

If the delayed onset reaction was hives with wheals lasting several hours and leaving no marks, then the hives were very likely from her underlying chronic urticaria and not specifically related to the amoxicillin challenge.

It would be alright to use amoxicillin or other penicillins in the future if clinically indicated for a documented bacterial infection. Given that the patient had no reaction within an hour of the amoxicillin, her risk of future anaphylaxis is not greater than random in the population, about 1 in 225,000.

If this patient's chronic urticaria is still active, any future infection will also be likely to cause a flare of her hives, whether she receives an antibiotic or not.

Dr. Jacqueline A. Pongracic, FAAAAI