Drug interactions
Diazepam + Phenytoin
Severity: Moderate
Diazepam and Phenytoin: moderate interaction.
Last updated
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
Phenytoin induces the metabolism of diazepam and may reduce its effect. Diazepam can also alter phenytoin levels in either direction, which is unpredictable and matters in seizure control.
What this interaction means in plain words
Diazepam and Phenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Diazepam belongs to Musculoskeletal; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4 and CYP2C19, increasing diazepam clearance; diazepam may variably affect phenytoin metabolism.
What to do
Monitor clinical response to diazepam and check serum phenytoin concentrations when diazepam is started or stopped. Adjust doses based on effect and levels.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Diazepam
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 Diazepam with Phenytoin?
MediHelp rates the interaction as moderate. Diazepam and Phenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin induces the metabolism of diazepam and may reduce its effect. Diazepam can also alter phenytoin levels in either direction, which is unpredictable and matters in seizure control.
How serious is the interaction between Diazepam and Phenytoin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor clinical response to diazepam and check serum phenytoin concentrations when diazepam is started or stopped. Adjust doses based on effect and levels.
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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