Use of penicillin in a patient with a history of cephalosporin allergy

* Aminocephalosporins: The seven aminocephalosporins and two aminopenicillins should all be considered potentially cross-reactive.

• Cefadroxil, cefprozil, and cefatrizine have the same side chain as amoxicillin.
• Cephalexin, cephadrine, cefaclor, and cephaloglycin have the same side chain as ampicillin.

Note that cross-reactivity among these drugs is up to 30% in European studies; rates in the United States have not been firmly established.
¶ For details of penicillin skin testing protocols, refer to UpToDate content on penicillin skin testing.
Δ Skin testing with aminocephalosporins is not performed in the United States and many other countries because sterile parenteral formulations are not available.
◊ Ampicillin is the only parenteral aminopenicillin available in the United States and many other countries.
§ If use of aztreonam or carbapenems is desired, refer to UpToDate content in the topic on the allergy evaluation for immediate cephalosporin reactions.
¥ Refer to the UpToDate topic on rapid drug desensitization for immediate hypersensitivity reactions for a discussion on safe performance of these protocols.
‡ Safe performance of graded challenges for immediate drug allergy are discussed in the UpToDate topic on the allergy evaluation for immediate cephalosporin reactions.
† Note that tolerance to a penicillin that is not an aminopenicillin, such as penicillin VK or penicillin G, does not prove tolerance to aminopenicillins. Thus, if an aminopenicillin is needed, it should be given using a graded challenge.