Drug interactions
Diazepam + Phenobarbital
Severity: Major
Diazepam and Phenobarbital: 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
Phenobarbital and diazepam together produce additive sedation and respiratory depression. Phenobarbital induces CYP enzymes and may lower diazepam concentrations during chronic use, while diazepam may change phenobarbital levels variably.
What this interaction means in plain words
Diazepam 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
Additive GABA-A mediated CNS depression and hepatic enzyme induction by phenobarbital increasing diazepam metabolism.
What to do
Monitor sedation and respiratory status, especially with parenteral dosing or in the elderly. Adjust diazepam dose to clinical response and monitor phenobarbital levels in epilepsy.
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 Diazepam
Frequently asked questions
Can I take Diazepam with Phenobarbital?
MediHelp rates the interaction as major. Diazepam 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. Phenobarbital and diazepam together produce additive sedation and respiratory depression. Phenobarbital induces CYP enzymes and may lower diazepam concentrations during chronic use, while diazepam may change phenobarbital levels variably.
How serious is the interaction between Diazepam 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 sedation and respiratory status, especially with parenteral dosing or in the elderly. Adjust diazepam dose to clinical response and monitor phenobarbital levels in epilepsy.
What other medicines interact with Diazepam?
MediHelp also lists interactions of Diazepam with, for example, Calcium / magnesium / potassium / sodium oxybates, Alfentanil, Alprazolam. The full list is on the Diazepam page.
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