Drug interactions
Chloramphenicol + Phenobarbital
Severity: Major
Chloramphenicol and Phenobarbital: major interaction.
Last updated Sources: UK SmPC
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 raise phenobarbital concentrations, increasing sedation and toxicity. Phenobarbital can also lower chloramphenicol concentrations, which may compromise antibacterial efficacy.
What this interaction means in plain words
Chloramphenicol and Phenobarbital 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.
Why it happens
Chloramphenicol inhibits hepatic metabolism of phenobarbital, while phenobarbital induces enzymes that clear chloramphenicol.
What to do
Monitor phenobarbital levels and signs of CNS depression, and monitor chloramphenicol serum concentrations with dose adjustment. Consider alternative antimicrobials.
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
- Phenobarbital Colonis 50 mg/5 ml Oral Suspension - SmPC sections 4.3/4.5 (names the partner; "en used in conjunction with dextropropoxyphene. • Antibacterials - there is a possibility of increased phenobarbital levels during concomitant use of chloramphe") — electronic medicines compendium (UK SmPC)
Other interactions of Chloramphenicol
Frequently asked questions
Can I take Chloramphenicol with Phenobarbital?
MediHelp rates the interaction as major. Chloramphenicol and Phenobarbital 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 raise phenobarbital concentrations, increasing sedation and toxicity. Phenobarbital can also lower chloramphenicol concentrations, which may compromise antibacterial efficacy.
How serious is the interaction between Chloramphenicol and Phenobarbital?
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 phenobarbital levels and signs of CNS depression, and monitor chloramphenicol serum concentrations with dose adjustment. Consider alternative antimicrobials.
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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