Drug interactions
Isoniazid + Simvastatin
Severity: Moderate
Isoniazid 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
Simvastatin is highly dependent on CYP3A4 for clearance, and its exposure rises with enzyme inhibition, increasing the risk of myopathy and rhabdomyolysis. Isoniazid is a weak to moderate inhibitor, so the effect is likely smaller than with strong inhibitors. Isoniazid hepatotoxicity may add to the concern.
What this interaction means in plain words
Isoniazid 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.
Isoniazid belongs to Anti Bacterial; Simvastatin belongs to Cardiovascular.
Why it happens
Isoniazid inhibits CYP3A4, which may reduce simvastatin first-pass and systemic clearance.
What to do
Monitor for muscle symptoms and check creatine kinase if they appear, keeping the simvastatin dose low. Consider switching to a statin less dependent on CYP3A4, such as pravastatin or rosuvastatin, during isoniazid therapy.
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 Isoniazid
Other interactions of Simvastatin
- Atazanavir + Simvastatin Contraindicated
- Clarithromycin + Simvastatin Contraindicated
- Cobicistat + Simvastatin Contraindicated
- Cyclosporin + Simvastatin Contraindicated
- Danazol + Simvastatin Contraindicated
- Darunavir + Simvastatin Contraindicated
Frequently asked questions
Can I take Isoniazid with Simvastatin?
MediHelp rates the interaction as moderate. Isoniazid 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. Simvastatin is highly dependent on CYP3A4 for clearance, and its exposure rises with enzyme inhibition, increasing the risk of myopathy and rhabdomyolysis. Isoniazid is a weak to moderate inhibitor, so the effect is likely smaller than with strong inhibitors. Isoniazid hepatotoxicity may add to the concern.
How serious is the interaction between Isoniazid 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 for muscle symptoms and check creatine kinase if they appear, keeping the simvastatin dose low. Consider switching to a statin less dependent on CYP3A4, such as pravastatin or rosuvastatin, during isoniazid therapy.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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