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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 Antibacterials: carbapenem and valproate interaction?

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.

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Antibacterials: carbapenem… MCQ (B7-PHARM5-25)

Q: What is the answer to this Pharmacology question?

The best answer is C, Replace the carbapenem with another suitable antibiotic, as carbapenems sharply lower valproate levels. Carbapenems cause a rapid and large fall in serum valproate, often to subtherapeutic levels within a day or two, by inhibiting acylpeptide hydrolase, which normally regenerates valproate from its glucuronide, so more is lost as the glucuronide.

Q: What concept does this question test?

It tests Antibacterials: carbapenem and valproate interaction in Pharmacology. The effect is not reliably overcome by raising the dose, and levels stay low until a few days after the carbapenem is stopped. The preferred management is to avoid the combination.

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Pharmacology · Antibacterials: carbapenem and valproate interaction

Sample item

A 30-year-old man with epilepsy has been seizure-free on sodium valproate. He is admitted with sepsis and given meropenem, and develops breakthrough seizures with a very low serum valproate level. Which course is most appropriate?

AStop valproate, as the combination causes hyperammonaemic encephalopathyBContinue meropenem and increase the valproate dose, as the fall is easily overcome by dose escalationCReplace the carbapenem with another suitable antibiotic, as carbapenems sharply lower valproate levelsDGive pyridoxine, as the seizures are caused by carbapenem-induced vitamin B6 deficiency

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

The answer and the reasoning

C. Replace the carbapenem with another suitable antibiotic, as carbapenems sharply lower valproate levels

Carbapenems cause a rapid and large fall in serum valproate, often to subtherapeutic levels within a day or two, by inhibiting acylpeptide hydrolase, which normally regenerates valproate from its glucuronide, so more is lost as the glucuronide. The effect is not reliably overcome by raising the dose, and levels stay low until a few days after the carbapenem is stopped. The preferred management is to avoid the combination.

Option by option

A. Stop valproate, as the combination causes hyperammonaemic encephalopathy
Valproate hyperammonaemia is a separate effect and is not the explanation for the fall in level.
B. Continue meropenem and increase the valproate dose, as the fall is easily overcome by dose escalation
Dose escalation does not reliably overcome the interaction, and levels remain low while the carbapenem is given.
C. Replace the carbapenem with another suitable antibiotic, as carbapenems sharply lower valproate levels (correct)
Correct. Avoiding carbapenems in patients on valproate prevents loss of seizure control.
D. Give pyridoxine, as the seizures are caused by carbapenem-induced vitamin B6 deficiency
Carbapenems do not cause vitamin B6 deficiency; pyridoxine is relevant to isoniazid toxicity.

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.

Antibacterials: carbapenem and valproate interaction: practice question

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The answer and the reasoning

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