Simvastatin and Nelfinavir: 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
Nelfinavir
Simvastatin
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 should not be taken together. Nelfinavir (Viracept) blocks the liver enzyme that normally breaks down simvastatin (Zocor). When that happens, simvastatin builds up in your body, with blood levels roughly six times higher than normal.
Too much simvastatin can hurt your muscles. Watch for unexplained muscle pain, tenderness, weakness, or dark or brown urine. In rare cases this can lead to serious muscle breakdown. The good news is your care team can manage this easily, usually by pausing your simvastatin while you are on nelfinavir. Please talk with your pharmacist or doctor before changing anything on your own.
Contraindicated combination. Nelfinavir is a strong CYP3A4 inhibitor; simvastatin is a CYP3A4 substrate (active drug, not a prodrug). Inhibition markedly reduces simvastatin clearance.
- Direction/magnitude: Simvastatin AUC increased ~6-fold and Cmax ~6.2-fold (another study: +505% AUC, +517% Cmax).
- Effect: Dose-dependent increased risk of myopathy and rhabdomyolysis.
- Evidence: Established.
- Management: Avoid concurrent use. If nelfinavir is required, temporarily suspend simvastatin for the duration of nelfinavir therapy. Monitor for muscle symptoms and consider CK if myopathy suspected.
What happens
An increased risk of myopathy or rhabdomyolysis
Interaction Deep Dive
Taking simvastatin together with a potent CYP3A4 inhibitor like nelfinavir can heighten the likelihood of myopathy and rhabdomyolysis, so this combination is contraindicated. When nelfinavir was given alongside simvastatin, the AUC of simvastatin rose 6-fold and its Cmax rose 6.2-fold. Should the two agents need to be used together, simvastatin should be paused for as long as nelfinavir therapy continues1. A separate study found that this identical regimen raised simvastatin AUC by 505% and Cmax by 517% 2.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of simvastatin
How to manage this interaction
This combination is contraindicated, but your care team can manage it. The standard approach is to temporarily stop simvastatin while you are taking nelfinavir, then resume it afterward as directed.
- Do not stop or change either medicine on your own; talk with your prescriber or pharmacist first.
- Your team may pause simvastatin, or choose a different cholesterol medicine, for the time you are on nelfinavir.
- Report any muscle pain, tenderness, weakness, or dark urine right away.
Keep taking your medicines as prescribed until your care team tells you how to adjust.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) When nelfinavir 1250 mg twice daily for 14 days was given together with simvastatin 20 mg once daily for 28 days, simvastatin AUC rose 6-fold and Cmax rose 6.2-fold, compared with simvastatin given by itself 1.
b) In a pharmacokinetic study involving 16 subjects, giving nelfinavir 1250 mg twice daily for 14 days along with a 28 day course of simvastatin 20 mg once daily produced increases in simvastatin mean AUC (505%; 90% confidence interval (CI), 393% to 643%) and Cmax (517%; 90% CI, 367% to 715%) 2.
Common questions
Can I take Simvastatin and Nelfinavir together?
Nelfinavir sharply raises simvastatin levels (about 6-fold), which can cause serious muscle damage, so the two should not be used together; your care team will typically pause simvastatin during nelfinavir treatment. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Simvastatin and Nelfinavir interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Simvastatin and Nelfinavir interaction managed?
This combination is contraindicated, but your care team can manage it. The standard approach is to temporarily stop simvastatin while you are taking nelfinavir, then resume it afterward as directed. Do not stop or change either medicine on your own; talk with your prescriber or pharmacist first. Your team may pause simvastatin, or choose a different cholesterol medicine, for the time you are on ne… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "established". Well documented — supported by controlled studies or strong clinical data.
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 Nelfinavir 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 (2)
- Product Information: ZOCOR(R) oral tablets, simvastatin oral tablets. Organon & Co (per FDA), Jersey City, NJ, 2022. DailyMed
- Product Information: VIRACEPT(R) oral film coated tablets, oral powder, nelfinavir mesylate oral film coated tablets, oral powder. Pfizer Inc (per Dailymed), New York, NY, 2023. DailyMed
Keep reading about Nelfinavir
Keep reading about Simvastatin
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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