Simvastatin and Fosamprenavir: 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
Fosamprenavir
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.
Let's talk about taking fosamprenavir (Lexiva) together with simvastatin (Zocor). Your body uses a liver enzyme called CYP3A4 to break down simvastatin and clear it out. Fosamprenavir slows that enzyme down, so simvastatin can build up to higher levels than it should.
When simvastatin gets too high, it raises the chance of a serious muscle problem. This can start as unexplained muscle pain, tenderness, or weakness, and in rare cases it can seriously affect the muscles and kidneys. Because of this risk, these two are not meant to be taken together. The good news is your care team has other options, so please talk with your pharmacist or doctor before combining them.
Contraindicated combination. Fosamprenavir is a CYP3A4 inhibitor (and CYP3A4 substrate); simvastatin is extensively metabolized by CYP3A4. Coadministration is expected to reduce simvastatin clearance, raising simvastatin exposure (AUC/Cmax) and the risk of myopathy and rhabdomyolysis.
- Direction: increased simvastatin effect/toxicity
- Onset: delayed
- Evidence: theoretical (mechanism-based)
- Management: avoid the combination. Select a statin not dependent on CYP3A4 (per prescriber judgment). If a statin is required, monitor for muscle symptoms and CK, and evaluate renal function if rhabdomyolysis is suspected.
What happens
An increased risk of myopathy or rhabdomyolysis
Interaction Deep Dive
Combining fosamprenavir with simvastatin is contraindicated because of the possibility of serious adverse effects, including the risk of myopathy and rhabdomyolysis1. In addition to being metabolized via CYP3A4, fosamprenavir also inhibits the CYP3A4 isoenzyme1. Because simvastatin metabolism likewise relies substantially on the CYP3A4 isoenzyme2, fosamprenavir may competitively block the metabolism of simvastatin, which in turn raises the likelihood of simvastatin toxicity.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated simvastatin metabolism
How to manage this interaction
This pairing is flagged as one to avoid, so the main step is choosing a safer plan rather than adjusting a dose.
- Keep taking both medicines as currently prescribed until you speak with your care team. Do not stop either on your own.
- Your prescriber may switch you to a different cholesterol medicine that is not affected the same way, or adjust your regimen and monitor you more closely.
- Report any unexplained muscle pain, tenderness, weakness, or dark-colored urine right away.
- Ask your pharmacist to review all your medicines so this combination can be caught and managed.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Simvastatin and Fosamprenavir together?
Fosamprenavir can make simvastatin build up and raise the risk of serious muscle damage, so this combination should be avoided. Talk with your doctor or pharmacist about a safer cholesterol medicine. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Simvastatin and Fosamprenavir interaction?
It is rated contraindicated. These should generally not be used together.
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 Fosamprenavir interaction managed?
This pairing is flagged as one to avoid, so the main step is choosing a safer plan rather than adjusting a dose. Keep taking both medicines as currently prescribed until you speak with your care team. Do not stop either on your own. Your prescriber may switch you to a different cholesterol medicine that is not affected the same way, or adjust your regimen and monitor you more closely. Report any u… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
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 Fosamprenavir 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)
Keep reading about Fosamprenavir
Keep reading about Simvastatin
These medications also interact with supplements
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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