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A 21-year-old member asked:

I'm allergic to penicillin, can i take keflex?

3 doctor answers12 doctors weighed in
Dr. Alex Martinez
Specializes in Allergy
Maybe: Penicillins (like amoxil) & cephalosporins (like keflex) are both beta-lactam antibiotics named because of their ringed chemical structure. Allergy to penicillins is sometimes directed against this ring, and an allergic reaction may also occur if a similar antibiotic is taken. It is estimated that about 10% of penicillin-allergic patients are also allergic to cephalosporins like keflex.
Dr. Gary Moss
30 years experience
Probably: Most doctors are concerned about cross reactivity between penicillins and cephalosporins, including keflex. In actuality, the cross-reactivity is uncommon between these two classes. Also, most people who think that they are allergic to penicillin are not. An allergist can test to see wether you are allergic to penicillin. He could also confirm whether it would be safe to take keflex.
Dr. Brant Ward
Allergy and Immunology 14 years experience
Likely, not certain: The majority of people who are told they are allergic to penicillin are not actually so (they get rashes for other reasons, e.g.). Of those that are allergic, about 70% or more will lose the allergy after about 10 years. If you are still allergic, there is about a 10% chance of cross-reaction to 1st-gen cephalosporins like keflex. An allergist can perform testing to judge your risk for a reaction.

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Similar questions

A 42-year-old member asked:

If i'm allergic to penicillin is it safe to take keflex pulvales?

1 doctor answer1 doctor weighed in
Dr. Paul Carter
A Verified Doctoranswered
31 years experience
No: If you are truly allergic to penicillin, you should avoid all penicillin derivatives and the first generation cephalosporins. Keflex is a first gen. Cephalosporin and may cross react with penicillin. See a board certified allergist to help you determine if penicillin is a true allergy for you.
Last updated Dec 7, 2019


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