bignail asked
I'm allergic to to amoxicillin, penicillin... any antibiotic in that category. Will it be safe to take cefdinir?
Answer
It's a common belief that if you are allergic to penicillin antibiotics, you may also be allergic to the cephalosporin class of antibiotics (which includes cephalexin and cefdinir) as well. This has been a long held belief but recent data suggests there is a much less chance of cross-reactivity than previously thought.
Penicillin - Cephalosporin cross reactivity
Cephalosporin antibiotics share a similar chemical structure to penicillin antibiotics. Below, you can see the similarities between cephalexin, a "first generation cephalosporin", and penicillin:
Past studies have listed around a 10% chance of being allergic to cephalosporin drugs if you were confirmed allergic to penicillin. We now know this rate is significantly lower. It appears that the older studies that reported the elevated rate may have used cephalosporin products that were contaminated with penicillin.
Current data suggests that cross-reactivity rates range between 0.2% and 0.7%. In addition, cases of cross-reactivity only occurred when using first generation cephalosporins such as cephalexin. Recent studies have shown that the cross-reactivity rate with third generation cephalosporins is near 0%.
The general consensus now is that penicillin - cephalosporin cross reactivity rates are extremely low. In addition, later generation (e.g. third and fourth) cephalosporins exhibit a near 0% cross-reactivity rate.
The cephalosporin referred to in the question, cefdinir, is classified as a third generation cephalosporin. It would be extremely uncommon for a penicillin allergic patient to experience a cross-reactivity reaction on this medication.
Lastly, the American Academy Of Pediatrics states there is no evidence base to restrict second or third generation cephalosporin medications in those with a history of penicillin allergies.
