Idelalisib and Simvastatin: 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
Idelalisib
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 don't mix well. Idelalisib (Zydelig) is a strong blocker of a liver enzyme called CYP3A4. That enzyme is what your body uses to break down simvastatin (Zocor). When idelalisib slows that breakdown, simvastatin can build up to much higher levels than intended.
Too much simvastatin raises the risk of muscle problems, including serious muscle breakdown (called rhabdomyolysis) that can harm the kidneys. Warning signs are unexplained muscle pain, tenderness, weakness, or dark-colored urine. This combination is considered off-limits, but the good news is your care team has clear ways to handle it. Talk with your doctor or pharmacist before taking both, and report any muscle symptoms right away.
Contraindicated combination. Idelalisib is a strong CYP3A4 inhibitor. Simvastatin is extensively metabolized by CYP3A4, so coadministration markedly increases simvastatin exposure (AUC/Cmax), raising the risk of dose-dependent myopathy and rhabdomyolysis.
- Direction: increased simvastatin effect/toxicity (inhibition, not a prodrug scenario).
- Evidence: theoretical/mechanistic, but interaction class is well established for strong CYP3A4 inhibitors with simvastatin.
- Onset: unspecified; assume risk throughout co-exposure.
- Management: avoid the combination. If idelalisib is required, temporarily suspend simvastatin for the duration of therapy. Monitor for muscle pain/weakness and consider CK if symptomatic.
What happens
Increased simvastatin concentrations and risk of myopathy and rhabdomyolysis
Interaction Deep Dive
Because of the risk of serious harm, including myopathy and rhabdomyolysis, simvastatin should not be given together with a potent CYP3A4 inhibitor1 like idelalisib 2. When such combined use cannot be avoided, simvastatin should be put on hold for as long as the strong CYP3A4 inhibitor is being administered 1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated simvastatin metabolism by idelalisib
How to manage this interaction
What your care team may do:
- Because this pairing is contraindicated, they will usually avoid using them together.
- If idelalisib treatment is needed, simvastatin is typically paused for the duration of idelalisib therapy, then resumed afterward under guidance.
- They may consider an alternative cholesterol medicine that is less affected by CYP3A4.
What you should do: Keep taking both exactly as prescribed until you speak with your prescriber or pharmacist, and do not stop anything on your own. Bring this interaction to their attention promptly, and report any muscle pain, tenderness, weakness, or dark urine right away.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Idelalisib and Simvastatin together?
Idelalisib can raise simvastatin levels enough to risk serious muscle damage, so this combination is generally avoided. Contact your prescriber or pharmacist promptly; they will typically pause simvastatin while you are on idelalisib. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Idelalisib and Simvastatin 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 Idelalisib and Simvastatin interaction managed?
What your care team may do: Because this pairing is contraindicated, they will usually avoid using them together. If idelalisib treatment is needed, simvastatin is typically paused for the duration of idelalisib therapy, then resumed afterward under guidance. They may consider an alternative cholesterol medicine that is less affected by CYP3A4. What you should do: Keep taking both exactly as presc… 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 Idelalisib or Simvastatin 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 Idelalisib
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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