Working on a module reviewing adverse drug reactions (NOT COVID RELATED), but got really excited about this little pharm/clinical pearl, so~
Should a penicillin allergy prevent you from prescribing a cephalosporin?
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Should a penicillin allergy prevent you from prescribing a cephalosporin?
#medtwitter #tweetorial @medtweetorial
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Beta-lactam antibiotics all share a (you guessed it) beta-lactam ring. Initially, cross-reactivity was thought to be due to antigenicity of the beta-lactam ring itself.
But no!
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But no!
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A meta-analysis showed first-gen cephalosporins had higher cross-reactivity rates in pts w/ penicillin allergies than second-gen cephalosporins.
Why?
They share an R1 side chain.
pubmed.ncbi.nlm.nih.gov/17321857/
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Why?
They share an R1 side chain.
pubmed.ncbi.nlm.nih.gov/17321857/
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Cross-reactivity depends on the specific chemical structure of the antibiotics.
Penicillins only share a side chain w/ first-gen cephalosporins. Due to this structural difference, second-gen cephalosporins don't trigger an immune response in penicillin-allergic patients.
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Penicillins only share a side chain w/ first-gen cephalosporins. Due to this structural difference, second-gen cephalosporins don't trigger an immune response in penicillin-allergic patients.
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This is also important when choosing between cephalosporins, which can differ through both the R1 side chain as well as an R2 side chain.
Since we don't know exactly which one is antigenic, it's safest to avoid similarities in either side chain.
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Since we don't know exactly which one is antigenic, it's safest to avoid similarities in either side chain.
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Carbapenams and monobactams are structurally different enough that there is little to no cross-reactivity w/ penicillin or cephalosporin allergies.
The exception: aztreonam shares an identical R1 side chain as ceftazidime.
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The exception: aztreonam shares an identical R1 side chain as ceftazidime.
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As a note, despite me lumping all penicillins together here, they often have different R1 side chains.
Therefore, penicillins don't necessarily even cross-react w/ each other!
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Therefore, penicillins don't necessarily even cross-react w/ each other!
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In summary:
- Cross-reactivity depends on sides chains, NOT the beta-lactam ring.
- You can therefore safely prescribe most beta-lactams even in pts w/ a documented beta-lactam allergy.
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- Cross-reactivity depends on sides chains, NOT the beta-lactam ring.
- You can therefore safely prescribe most beta-lactams even in pts w/ a documented beta-lactam allergy.
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For further more in-depth reading, I highly recommend the @iBookCC chapter written by @PulmCrit.
emcrit.org/ibcc/penicilli…
Includes a nice cross-reactivity chart!
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emcrit.org/ibcc/penicilli…
Includes a nice cross-reactivity chart!
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Sources:
Zagursky: doi.org/10.1016/j.jaip…
Chaudhry: doi.org/10.3390/pharma…
Molecular structures were borrowed from respective Wikipedia pages and edited in PPT.
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Zagursky: doi.org/10.1016/j.jaip…
Chaudhry: doi.org/10.3390/pharma…
Molecular structures were borrowed from respective Wikipedia pages and edited in PPT.
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Thanks for reading this small thread. Please let me know if you have any feedback!
