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July 6, 1970

Cross Reactivity Between Ampicillin and Penicillin G

JAMA. 1970;213(1):131. doi:10.1001/jama.1970.03170270071029

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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