Drug interactions
Phenobarbital + Simvastatin
Severity: Moderate
Phenobarbital and Simvastatin: 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
Phenobarbital is an inducer of CYP3A4 and can substantially lower simvastatin and active metabolite concentrations. This can reduce the cholesterol-lowering effect and weaken cardiovascular protection.
What this interaction means in plain words
Phenobarbital and Simvastatin 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.
Why it happens
Phenobarbital induces hepatic and intestinal CYP3A4, increasing simvastatin first-pass and systemic metabolism.
What to do
Monitor the lipid profile after starting or stopping phenobarbital and increase the statin dose or switch to a statin less dependent on CYP3A4 (e.g. rosuvastatin or pravastatin) if the response is inadequate.
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 Simvastatin
- Atazanavir + Simvastatin Contraindicated
- Clarithromycin + Simvastatin Contraindicated
- Cobicistat + Simvastatin Contraindicated
- Cyclosporine + Simvastatin Contraindicated
- Cyclosporin + Simvastatin Contraindicated
- Danazol + Simvastatin Contraindicated
Frequently asked questions
Can I take Phenobarbital with Simvastatin?
MediHelp rates the interaction as moderate. Phenobarbital and Simvastatin 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. Phenobarbital is an inducer of CYP3A4 and can substantially lower simvastatin and active metabolite concentrations. This can reduce the cholesterol-lowering effect and weaken cardiovascular protection.
How serious is the interaction between Phenobarbital and Simvastatin?
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 the lipid profile after starting or stopping phenobarbital and increase the statin dose or switch to a statin less dependent on CYP3A4 (e.g. rosuvastatin or pravastatin) if the response is inadequate.
What other medicines interact with Simvastatin?
MediHelp also lists interactions of Simvastatin with, for example, Atazanavir, Clarithromycin, Cobicistat. The full list is on the Simvastatin page.
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