Lithium Drug Interactions — ORE Part 1 MCQ

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HardPharmacology & TherapeuticsLithium Drug InteractionsORE Part 1

A 40-year-old patient on lithium therapy for bipolar disorder requires a dental extraction. In addition to avoiding NSAIDs, which other commonly prescribed dental drug interacts with lithium?

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Correct answer: B — Metronidazole

Metronidazole is the correct answer. The eMC SmPC documents that metronidazole may precipitate lithium toxicity by increasing serum lithium levels, particularly in patients on high doses, and strict monitoring is recommended. Metronidazole is commonly prescribed in dental practice for anaerobic infections and periodontal conditions. Paracetamol, amoxicillin, lidocaine, and chlorhexidine do not have documented significant interactions with lithium. The question tests knowledge beyond the well-known NSAID–lithium interaction to discriminate understanding of antibiotics that pose specific risk in patients on lithium therapy requiring dental treatment. NSAIDs reduce renal lithium clearance; metronidazole appears to increase serum lithium levels by a separate mechanism requiring clinical vigilance.

Reference: eMC Summary of Product Characteristics (Pylera, metronidazole component), https://www.medicines.org.uk/emc/product/15622/smpc; HPFT Safe Use of Lithium Guidelines (January 2024), https://www.hpft.nhs.uk/media/7243/safe-use-of-lithium-guidelines-final-jan-2024.pdf