Taking Omnicef With A Penicillin Allergy

Our pharmacist answers the latest question regarding taking the antibiotic Omnicef (cefdinir) if you have a penicillin allergy.

Oct 02, 2017

Jan asked

Hello, my Dr. has prescribed me Omnicef for a sinus infection that is being stubborn and I am allergic to penicillin. I have previously taken cephalexin roughly 10 years ago with no side effects. Should I have any issues taking Omnicef?

Answer

Both Omnicef and Cephalexin are drugs in a class known as cephalosporins. They are NOT considered to be of the penicillin class although there is a SMALL chance of cross reactivity. Current data suggest that the rate of cross-reactivity between penicillins and cephalosporins is probably less than 1%.

In general, the rate of allergic cross-reactivity is highest between penicillins and first-generation cephalosporins (cephalexin is a first generation) . The chance is MUCH less with later generation drugs (Omnicef is a later generation).Seeing as how you were OK on cephalexin, I must imagine you should be just fine on Omnicef.

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