Phenobarbital and Clindamycin: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 1, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenobarbital
Clindamycin
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
Here's what's going on. Phenobarbital is a medicine that can speed up the liver's ability to break down other drugs. Clindamycin, an antibiotic, is partly cleared by one of those same liver pathways (called CYP3A). So when they are taken together, your body may clear the clindamycin faster than usual, which could leave less of it in your system to fight the infection.
The good news: this is based on theory, not strong real-world reports. Your care team can manage it by watching how well the infection is responding and adjusting the clindamycin dose if needed. Keep taking both exactly as prescribed, and ask your pharmacist or doctor if you have any concerns.
Mechanism: Phenobarbital is a potent inducer of CYP3A. Clindamycin is partly metabolized by CYP3A to its active/inactive metabolites, so induction may increase clindamycin clearance and lower systemic exposure (AUC/Cmax), potentially reducing antibacterial efficacy. Neither agent's effect here depends on prodrug activation for the antibacterial parent.
- Direction: reduced clindamycin exposure and efficacy
- Onset: unspecified (enzyme induction is typically delayed, days to weeks)
- Evidence: theoretical
- Severity on file: major
Management: If co-administration is unavoidable, monitor clinical/microbiologic response, watch neonates closely, and consider an increased clindamycin dose individualized by the care team.
What happens
Reduced CYP3A substrate exposure and reduced efficacy of CYP3A substrate
Interaction Deep Dive
When PHENobarbital, which induces CYP3A, is taken together with a CYP3A substrate, the exposure to that substrate may fall, potentially lowering its efficacy. Where such combined use cannot be prevented, monitor neonates carefully and consider raising the CYP3A substrate dose as needed1.
Why it happens (mechanism)
Induction of CYP3A-mediated metabolism of CYP3A substrates
How to manage this interaction
What your care team may do:
- Watch how well the infection is responding to clindamycin, since phenobarbital may lower clindamycin levels.
- Consider adjusting (often increasing) the clindamycin dose if needed, individualized by your team.
- Monitor especially closely in newborns/neonates.
What you should do:
- Keep taking both medicines exactly as prescribed. Do not start, stop, or change doses on your own.
- Tell your pharmacist or prescriber if the infection is not improving as expected.
- Mention any other medicines you take, since phenobarbital can affect many of them.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Phenobarbital and Clindamycin together?
Phenobarbital may lower clindamycin levels and could make the antibiotic less effective, so your care team may monitor your response and adjust the clindamycin dose. Keep taking both as prescribed and speak up if the infection isn't improving. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Phenobarbital and Clindamycin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Phenobarbital and Clindamycin interaction managed?
What your care team may do: Watch how well the infection is responding to clindamycin, since phenobarbital may lower clindamycin levels. Consider adjusting (often increasing) the clindamycin dose if needed, individualized by your team. Monitor especially closely in newborns/neonates. What you should do: Keep taking both medicines exactly as prescribed. Do not start, stop, or change doses on your o… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Phenobarbital or Clindamycin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: SEZABY(TM) intravenous injection, phenobarbital sodium intravenous injection. Sun Pharmaceutical Industries Inc (per manufacturer), Cranbury, NJ, 2022. DailyMed
Keep reading about Phenobarbital
Keep reading about Clindamycin
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