The 10% cross reactivity rate between penicillin’s and cephalosporins is a myth. Multiple studies have shown that in reality, it is only around 1% and applies to 1st and 2nd generation cephalosporins in those with an anaphylactic penicillin allergy.

I have given Rocephin numerous times to individuals with an anaphylactic penicillin allergy with no ill effect. I have prescribed Cefdinir thousands of times to patients with a penicillin allergy without issue.

The use of 3rd and 4th generation cephalosporins in individuals with penicillin has negligible risk. It is considered safe.

Do not let this myth prevent you from prescribing cephalosporins to penicillin allergic patients in necessary scenarios.

As always, use your own clinical judgement.