Letermovir and Clindamycin: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 1, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Letermovir
Clindamycin
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 slow down one of the liver's cleanup enzymes called CYP3A. Clindamycin is partly broken down by that same enzyme. So when you take them together, clindamycin can build up a bit higher in your body than usual. That could make antibiotic side effects, like stomach upset or diarrhea, a little more likely.
The good news is this is very manageable. Your care team knows about this kind of interaction and can watch how you're doing and adjust your clindamycin dose if needed. Please keep taking both medicines as prescribed, and let your pharmacist or doctor know if you notice new or worse side effects.
Effect: Letermovir is a moderate CYP3A inhibitor; clindamycin is a CYP3A substrate. Coadministration may increase clindamycin exposure (increased AUC/Cmax) via reduced CYP3A-mediated metabolism.
- Direction: increased substrate exposure (stronger effect / more adverse effects).
- Magnitude: not established for clindamycin; the reference midazolam study showed AUC increases of ~47% (IV) to ~125% (oral).
- Onset: unspecified; Evidence: probable.
- Management: monitor for enhanced clindamycin effect and GI adverse effects; dose may be individualized by the care team.
What happens
Increased CYP3A substrate exposure
Interaction Deep Dive
Taking letermovir together with a CYP3A substrate can raise the exposure of that substrate. One drug interaction study examined this: when letermovir (240 mg orally once daily) was given alongside the CYP3A substrate midazolam (single 1 mg IV dose), midazolam's AUC rose by 47%, its Cmax by 5%, and its C24hr by 174%. In the same study, combining letermovir (240 mg orally once daily) with midazolam administered as a single 2 mg oral dose produced increases of 125% in midazolam AUC and 72% in Cmax1.
Why it happens (mechanism)
Inhibition of CYP3A-substrate metabolism by letermovir
How to manage this interaction
This interaction is manageable with awareness and monitoring.
- Keep taking both letermovir and clindamycin exactly as prescribed unless your care team tells you otherwise.
- Your team may monitor you more closely for antibiotic side effects, and your clindamycin dose may need to be adjusted and individualized.
- Report new or worsening symptoms such as diarrhea, stomach pain, nausea, or signs of severe gut irritation.
- Make sure your pharmacist and prescriber both know you are taking these two together so they can review it.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a drug interaction study, giving letermovir (oral 240 mg once daily) together with a CYP3A substrate, midazolam (1 mg single dose IV), raised midazolam AUC, Cmax and C24hr by 47%, 5% and 174%, respectively. Additionally, giving letermovir (oral 240 mg once daily) together with midazolam (2 mg single dose orally) raised midazolam AUC and Cmax by 125% and 72%, respectively 1.
Common questions
Can I take Letermovir and Clindamycin together?
Letermovir can raise clindamycin levels by slowing its breakdown, so watch for more antibiotic side effects and let your care team monitor and adjust as needed. Keep taking both as prescribed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Letermovir and Clindamycin 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 Clindamycin interaction managed?
This interaction is manageable with awareness and monitoring. Keep taking both letermovir and clindamycin exactly as prescribed unless your care team tells you otherwise. Your team may monitor you more closely for antibiotic side effects, and your clindamycin dose may need to be adjusted and individualized. Report new or worsening symptoms such as diarrhea, stomach pain, nausea, or signs of severe… 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 Clindamycin 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 Clindamycin
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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