Antimicrobials: penicillin allergy and cross-reactivity: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pharmacology · Antimicrobials: penicillin allergy and cross-reactivity

Sample item

A patient reports hives after amoxicillin and needs a cephalosporin for a serious infection. Which statement is correct?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Cross-reactivity is low, particularly with third-generation agents having dissimilar side chains, so they may be used with caution

The risk of cross-reactivity is only a few percent, driven mainly by similarity of the R1 side chain, as between amoxicillin and cefadroxil or cefaclor. Third-generation cephalosporins such as ceftriaxone have dissimilar side chains. Anaphylaxis history needs more care.

Option by option

  • A. Cross-reactivity is low, particularly with third-generation agents having dissimilar side chains, so they may be used with caution (correct)

    Correct. Cross-reactivity is low and depends on side chains.

  • B. Cross-reactivity is 100 percent

    Cross-reactivity is far less than 100 percent.

  • C. All cephalosporins are absolutely contraindicated

    Blanket avoidance is not required.

  • D. Penicillin allergy is a contraindication only for carbapenems

    Cross-reactivity with carbapenems is also low.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is A, Cross-reactivity is low, particularly with third-generation agents having dissimilar side chains, so they may be used with caution. The risk of cross-reactivity is only a few percent, driven mainly by similarity of the R1 side chain, as between amoxicillin and cefadroxil or cefaclor.

Why is "Cross-reactivity is 100 percent" not the answer?

Cross-reactivity is far less than 100 percent.

Why is "All cephalosporins are absolutely contraindicated" not the answer?

Blanket avoidance is not required.

Why is "Penicillin allergy is a contraindication only for carbapenems" not the answer?

Cross-reactivity with carbapenems is also low.

What concept does this question test?

It tests Antimicrobials: penicillin allergy and cross-reactivity in Pharmacology. Third-generation cephalosporins such as ceftriaxone have dissimilar side chains. Anaphylaxis history needs more care.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Antimicrobials: penicillin allergy and cross-reactivity?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.