Cross Reactivity Between Ampicillin and Penicillin G

Abstract

To the Editor:— Breese, in a recent issue ( 211 :837, 1970) stated: "The occurrence of an ampicillin rash does not mean that the patient is sensitive to other types of penicillin." This statement raises the more general question of cross-reactivity between penicillin G and ampicillin. So far as we know, no study of clinical or chemical cross-reactivity between these two drugs has been done. Fellner, in a personal communication, states he would predict that a patient with an anaphylactic reaction to one of these drugs would most likely show a similar reactivity to the other. We concur with this view and suggest that, until further studies are available, it is contraindicated to use ampicillin in a patient who has had a previous anaphylactic reaction to penicillin G. The reverse would similarly be true. Also, there are no published data regarding the occurrence of crossreactivity between ampicillin and penicillin G of