Cephalosporins constitute a large family of antibiotics. They are “kissing cousins” to the penicillin family, but are unique in their own right. Until recently it was thought that if a person was allergic to one cephalosporin, they would be allergic to the entire family.
Several research groups have questioned this conventional wisdom. Most recently the Italian Ministry for University Research did a large population study on this issue. They did both skin testing and clinical challenges (giving the patient a test dose) with several hundred patients known to be allergic to one type of cephalosporin.
As it turns out, most of these individuals were found to be skin-test negative and patient-challenge negative to at least one different cephalosporin. The basic cephalosporin molecule consists of a ring structure with variable side-chain molecules. The greater the difference in the side-chain molecule,
the greater the likelihood of no cross-reacting allergy.
The Italian researchers concluded that – especially in people with limited choices for available antibiotics and who have a known cephalosporin allergy – it is worth testing them to a cephalosporin with a different side-chain structure so as to find a safe alternate therapy.