Drug interactions
Chloramphenicol + Fosphenytoin
Severity: Major
Chloramphenicol and Fosphenytoin: 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 markedly raise phenytoin concentrations, and fosphenytoin is converted to phenytoin. This may cause phenytoin toxicity with nystagmus, ataxia, confusion, and in severe cases seizures or sedation.
What this interaction means in plain words
Chloramphenicol and Fosphenytoin 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; Fosphenytoin belongs to Central Nervous System.
Why it happens
Inhibition of CYP2C9/CYP2C19-mediated phenytoin metabolism.
What to do
Monitor phenytoin levels and for signs of toxicity, and reduce the fosphenytoin dose as needed. Recheck levels after chloramphenicol 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 Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Chloramphenicol with Fosphenytoin?
MediHelp rates the interaction as major. Chloramphenicol and Fosphenytoin 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 markedly raise phenytoin concentrations, and fosphenytoin is converted to phenytoin. This may cause phenytoin toxicity with nystagmus, ataxia, confusion, and in severe cases seizures or sedation.
How serious is the interaction between Chloramphenicol and Fosphenytoin?
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 levels and for signs of toxicity, and reduce the fosphenytoin dose as needed. Recheck levels after chloramphenicol 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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