Drug interactions
Chloramphenicol + Phenytoin
Severity: Major
Chloramphenicol and Phenytoin: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Chloramphenicol can substantially raise phenytoin concentrations and cause toxicity such as nystagmus, ataxia and confusion. The interaction is well described in case reports and studies.
What this interaction means in plain words
Chloramphenicol and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Chloramphenicol belongs to Anti Bacterial; Phenytoin belongs to Central Nervous System.
Why it happens
Inhibition of CYP2C9 and CYP2C19 metabolism of phenytoin.
What to do
Monitor phenytoin serum levels and clinical signs of toxicity during and after chloramphenicol therapy. Reduce the phenytoin dose as needed and recheck levels when the antibiotic is stopped.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Chloramphenicol
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Chloramphenicol with Phenytoin?
MediHelp rates the interaction as major. Chloramphenicol and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Chloramphenicol can substantially raise phenytoin concentrations and cause toxicity such as nystagmus, ataxia and confusion. The interaction is well described in case reports and studies.
How serious is the interaction between Chloramphenicol and Phenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor phenytoin serum levels and clinical signs of toxicity during and after chloramphenicol therapy. Reduce the phenytoin dose as needed and recheck levels when the antibiotic is stopped.
What other medicines interact with Chloramphenicol?
MediHelp also lists interactions of Chloramphenicol with, for example, Adagrasib, Avapritinib, Bcg vaccine live. The full list is on the Chloramphenicol page.
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