Simvastatin and Dalfopristin: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 4, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Simvastatin
Dalfopristin
No brand names on record
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.
These two medicines can clash. Simvastatin (Zocor) is a cholesterol drug your body clears using a liver enzyme called CYP3A4. Dalfopristin (part of quinupristin/dalfopristin, an antibiotic given in the hospital) blocks that enzyme. When it's blocked, simvastatin can build up higher than normal in your blood.
Too much simvastatin raises the risk of muscle problems, like aching, tenderness, or weakness. Rarely, this can become serious muscle breakdown. The good news is your care team can manage this easily by watching for symptoms and adjusting your statin dose. If you notice new muscle pain or weakness while on both, tell your doctor or pharmacist right away.
Mechanism: Quinupristin/dalfopristin is a potent CYP3A4 inhibitor. Simvastatin is a CYP3A4 substrate (not a prodrug relevant here), so concurrent use decreases its clearance and increases simvastatin exposure (AUC/Cmax), raising the risk of myopathy and rhabdomyolysis.
- Direction: Increased simvastatin effect/toxicity
- Onset: Delayed
- Evidence: Probable; severity major
- Management: Monitor for muscle pain, tenderness, weakness; check creatine kinase (CK). Discontinue simvastatin if CK rises markedly or myopathy/rhabdomyolysis is suspected. Consider dose reduction or temporary suspension of simvastatin during the antibiotic course, individualized by the care team.
What happens
An increased risk of myopathy or rhabdomyolysis
Interaction Deep Dive
As a strong inhibitor of the cytochrome P450 3A4 enzyme system, quinupristin/dalfopristin can raise simvastatin levels when the two agents are given together. Simvastatin dosing should be modified as needed, and patients need careful observation for indications of excessive simvastatin toxicity, including muscle weakness or pain1.
Why it happens (mechanism)
Inhibition of cytochrome P450-mediated metabolism of simvastatin
How to manage this interaction
What your team may do:
- Watch closely for muscle pain, tenderness, or weakness while you take both.
- Check your creatine kinase (CK) blood level if muscle symptoms appear.
- Adjust your simvastatin dose, which may need to be individualized, or pause it during the antibiotic course.
What you should do: Keep taking both exactly as prescribed unless your prescriber tells you otherwise. Report any new muscle aches, soreness, weakness, or dark-colored urine to your pharmacist or doctor promptly so they can act quickly.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Simvastatin and Dalfopristin together?
Dalfopristin can raise simvastatin levels and increase the risk of muscle damage, so watch for muscle pain or weakness and have your care team monitor you and adjust the statin dose as needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Simvastatin and Dalfopristin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How is the Simvastatin and Dalfopristin interaction managed?
What your team may do: Watch closely for muscle pain, tenderness, or weakness while you take both. Check your creatine kinase (CK) blood level if muscle symptoms appear. Adjust your simvastatin dose, which may need to be individualized, or pause it during the antibiotic course. What you should do: Keep taking both exactly as prescribed unless your prescriber tells you otherwise. Report any new mus… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Simvastatin or Dalfopristin 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: Synercid(R) I.V. quinupristin and dalfopristin. Rhone-Poulenc Rorer Pharmaceuticals Inc. Collegeville, PA, 1999.
Keep reading about Simvastatin
Keep reading about Dalfopristin
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