SUMMARIES FOR PATIENTS

Cephalosporin Allergy in Patients with Penicillin Allergy

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The summary below is from the full report titled "Cross-Reactivity and Tolerability of Cephalosporins in Patients with Immediate Hypersensitivity to Penicillins." It is in the 6 July 2004 issue of Annals of Internal Medicine (volume 141, pages 16-22). The authors are A. Romano, R.-M. Guéant-Rodriguez, M. Viola, R. Pettinato, and J.-L. Guéant.

What is the problem and what is known about it so far?

Allergic reactions to penicillin antibiotics are common. Cephalosporins are other antibiotics that fight many of the same infections as penicillin. They may be an option for patients who are allergic to penicillin. However, cephalosporins and penicillins have similar chemical structures. Some patients who are allergic to penicillin are also allergic to cephalosporin, but information about the frequency of cephalosporin allergy in patients with penicillin allergy is limited. With some drugs, such as penicillin and cephalosporin, doctors can perform a "skin test" for allergic reactions by administering small amounts of the drug under the skin. However, rather than perform a skin test, many doctors simply avoid cephalosporin in patients with penicillin allergy.

Why did the researchers do this particular study?

To determine the frequency of cephalosporin allergy in patients with known penicillin allergy.

Who was studied?

128 patients with a known penicillin allergy and positive results on skin tests for penicillin. These patients agreed to participate for research purposes only and did not actually have conditions that might require cephalosporin treatment.

How was the study done?

The researchers administered skin tests with 6 different cephalosporin antibiotics to all 128 patients. They then offered a cephalosporin challenge test to patients with negative results on skin tests for cephalosporin. In the challenge tests, the researchers gave them a single dose of 2 different cephalosporin antibiotics and observed the patients for an allergic reaction.

What did the researchers find?

Of the 128 patients tested, 14 had positive results on skin testing for at least one cephalosporin antibiotic. Patients with negative skin test results who agreed to a challenge test tolerated subsequent challenge doses of cephalosporin without an allergic reaction, but 22 patients declined challenge testing.

What were the limitations of the study?

Since 22 patients declined testing, the researchers cannot be certain that no patient with negative results on skin tests for cephalosporin would have had an allergic reaction with a challenge test. In addition, the challenge tests used single doses of the antibiotics. Some patients who showed no reaction to a challenge test might have had an allergic reaction to a full dose.

What are the implications of the study?

Since about 10% of patients with documented penicillin allergy also had positive results on skin tests for cephalosporin, physicians should avoid using cephalosporins in such patients unless they first do a skin test for cephalosporin allergy.