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Drug allergy: the rationale for oral challenge after negative penicillin skin tests

Question:

8/13/2017
As a practitioner in private practice, our office does not have access to a minor determinant. I have always followed negative penicillin testing with an oral challenge. I was recently told by a colleague that the oral challenge is not necessary. I checked with various sources and they all recommend an oral challenge. I am thinking the oral challenge is perhaps not necessary if a minor determinant is available (such as in the University setting). Again as a private practitioner, the minor determinant is not available, thus I have always followed the negative skin testing with an oral challenge.

Answer:

Thank you for your Ask the Expert question. We are grateful to Dr David Lang who provided the following response.

The rationale for administering an oral challenge, as you point out, includes the lack of a minor determinant mixture in combination with Prepen and PenG solutions for immediate hypersensitivity skin testing. The rationale for an oral challenge with 250 mg amoxicillin also includes ruling out the possibility, via this challenge, that side-chain specific IgE to amoxicillin/ampicillin is present (1) that has not been detected by skin testing with Prepen and PenG – which assesses the presence of IgE to the beta lactam ring. Also, we find the oral challenge is helpful from the standpoint of “experiential learning”: patients leave with piece of mind, knowing they’ve tolerated amoxicillin without adverse reaction.

1. Vega JM, Blanca M, Garcia JJ, et al. Immediate allergic reactions to amoxicillin. Allergy. 1994; 49: 317–322.

Jacqueline A. Pongracic, MD, FAAAAI