Letermovir 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
Letermovir
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.
Letermovir (Prevymis) can raise the level of simvastatin (Zocor) in your blood. Letermovir slows down the pathways your body uses to break down and clear simvastatin, so more of the statin builds up. That extra buildup raises the chance of muscle problems, including muscle pain and weakness, and rarely a serious muscle breakdown called rhabdomyolysis.
Because of this, using these two together is generally not recommended. Please don't stop or change either medicine on your own. Talk with your pharmacist or doctor. They can review your medicines and find a safe plan, such as a different statin, so you stay protected.
Effect: Letermovir increases simvastatin exposure, raising the risk of myopathy and rhabdomyolysis. Coadministration is not recommended.
Mechanism: Letermovir inhibits CYP3A-mediated metabolism and OATP1B1/OATP1B3-mediated hepatic uptake of simvastatin, increasing systemic and hepatic exposure.
- Magnitude: No simvastatin-specific data; atorvastatin AUC rose 229%, Cmax 117%. Simvastatin, a sensitive CYP3A/OATP substrate, is expected to be affected at least comparably.
- Onset: Unspecified. Evidence: Probable.
- Management: Avoid the combination; prefer an alternative statin. If use is unavoidable, monitor for muscle symptoms and CK.
What happens
Increased simvastatin exposure and an increased risk for myopathy and rhabdomyolysis
Interaction Deep Dive
Combining letermovir with simvastatin (a CYP3A/OATP1B1/OATP1B3 substrate and HMG-CoA reductase inhibitor) is advised against, because it can raise simvastatin exposure and thereby heighten the likelihood of myopathy and rhabdomyolysis. Data from a drug interaction study showed that when letermovir (480 mg orally once daily) was given alongside the HMG-CoA reductase inhibitor atorvastatin (a single 20 mg oral dose), atorvastatin's AUC, Cmax and C24hr rose by 229%, 117% and 262%, respectively. When letermovir (240 mg orally once daily) was administered with the CYP3A substrate midazolam (a single 1 mg IV dose), midazolam's AUC, Cmax and C24hr increased by 47%, 5% and 174%, respectively. Additionally, giving letermovir (240 mg orally once daily) together with midazolam (a single 2 mg oral dose) produced increases in midazolam's AUC and Cmax of 125% and 72%, respectively1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of simvastatin; inhibition of OATP1B1-mediated efflux transport of simvastatin; inhibition of OATP1B3-mediated efflux transport of simvastatin
How to manage this interaction
This combination is generally avoided. The safest approach your care team usually takes is choosing a different cholesterol medicine that isn't affected the same way, since combining letermovir and simvastatin can raise statin levels and muscle-injury risk.
- Keep taking both exactly as prescribed until you speak with your care team. Do not stop either one on your own.
- Ask your pharmacist or doctor whether an alternative statin would be better for you.
- Report any unexplained muscle pain, tenderness, weakness, or dark-colored urine right away.
Your team can manage this by selecting a safer option and, if needed, monitoring you more closely.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) In a drug interaction study, giving letermovir (480 mg once daily orally) together with the HMG-CoA reductase inhibitor atorvastatin (20 mg single dose orally) resulted in rises in atorvastatin AUC, Cmax and C24hr of 229%, 117% and 262%, respectively 1.
b) In a drug interaction study, administering letermovir (oral 240 mg once daily) alongside the CYP3A substrate midazolam (1 mg single dose IV) produced increases in midazolam AUC, Cmax and C24hr of 47%, 5% and 174%, respectively. Additionally, giving letermovir (oral 240 mg once daily) with midazolam (2 mg single dose orally) increased midazolam AUC and Cmax by 125% and 72%, respectively 1.
Common questions
Can I take Letermovir and Simvastatin together?
Letermovir raises simvastatin levels and the risk of serious muscle injury, so this pairing is generally avoided; ask your pharmacist or doctor about switching to a safer statin, and report any muscle pain or weakness. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Letermovir and Simvastatin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Letermovir and Simvastatin interaction managed?
This combination is generally avoided. The safest approach your care team usually takes is choosing a different cholesterol medicine that isn't affected the same way, since combining letermovir and simvastatin can raise statin levels and muscle-injury risk. Keep taking both exactly as prescribed until you speak with your care team. Do not stop either one on your own. Ask your pharmacist or doctor… 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 Letermovir 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 (1)
- Product Information: PREVYMIS(R) oral tablets, oral pellets, intravenous injection, letermovir oral tablets, oral pellets, intravenous injection. Merck Sharp & Dohme Corp (per FDA), Rahway, NJ, 2024. DailyMed
Keep reading about Letermovir
Keep reading about Simvastatin
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