Letermovir and Cariprazine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 16, 2026 · Source data updated Jul 16, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Letermovir
Cariprazine
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 can interact. Letermovir (Prevymis) slows down a liver enzyme called CYP3A4, which is the same enzyme your body uses to break down cariprazine (Vraylar). When that clean-up slows, cariprazine and its active breakdown product can build up higher than usual in your body.
That means you might feel stronger effects or more side effects from the cariprazine, such as restlessness, sleepiness, muscle stiffness, or shaky movements. The good news is that this is very manageable. Your care team can simply use a lower cariprazine dose while you are on letermovir and keep a closer eye on how you feel. Please don't change anything on your own, just talk with your doctor or pharmacist.
Effect: Letermovir (moderate CYP3A4 inhibitor) reduces CYP3A4-mediated metabolism of cariprazine (CYP3A4 substrate), increasing exposure to cariprazine and its active metabolite didesmethylcariprazine (DDCAR).
- Direction: Increased cariprazine/DDCAR exposure (increased drug effect).
- Severity/Evidence: Major; probable.
- Management (per labeling for moderate 3A4 inhibitors): When initiating cariprazine on a moderate inhibitor, use 1.5 mg every other day. If already stable on cariprazine 1.5 or 3 mg daily, reduce to 1.5 mg every other day; if on 4.5 or 6 mg daily, reduce to 1.5 mg once daily. On stopping letermovir, cariprazine dose may need to be increased per clinical response.
Monitor for EPS, akathisia, sedation, and tolerability.
What happens
Increased cariprazine and its major active metabolite (didesmethylcariprazine (DDCAR)) exposure
Interaction Deep Dive
Taking cariprazine (a CYP3A4 substrate) together with a moderate CYP3A4 inhibitor can raise the levels of both cariprazine and its active metabolite, didesmethylcariprazine. If cariprazine is being started in a patient already on a moderate CYP3A4 inhibitor (for schizophrenia or bipolar mania), begin with 1.5 mg orally every other day, then increase to 1.5 mg orally every other day if warranted and guided by clinical response and tolerability. For a patient on a moderate CYP3A4 inhibitor being treated for bipolar depression or receiving adjunctive therapy for MDD, use 1.5 mg orally every other day. When a moderate CYP3A4 inhibitor is added to a patient on a stable cariprazine dose: for those currently taking 1.5 or 3 mg once daily, change the cariprazine dose to 1.5 mg orally every other day upon starting the inhibitor. For those currently taking cariprazine 4.5 or 6 mg once daily, change the cariprazine dose to 1.5 mg orally once daily upon starting the inhibitor. Once the moderate CYP3A4 inhibitor is stopped, the cariprazine dose may require an increase according to clinical response and tolerability1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of cariprazine
How to manage this interaction
What your care team may do:
- Use a lower cariprazine dose while you are taking letermovir, since exposure to cariprazine and its active metabolite goes up.
- Watch you more closely for side effects like restlessness, drowsiness, or stiff or shaky movements.
- Re-adjust your cariprazine dose again if the letermovir is later stopped.
What you should do:
- Keep taking both medicines exactly as prescribed unless told otherwise.
- Tell your pharmacist or prescriber that you take both so the dose can be tailored to you.
- Report any new or worsening side effects promptly.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In drug interaction studies, giving cariprazine 1.5 mg/day together with erythromycin (a moderate CYP3A4 inhibitor) 500 mg twice daily for 21 days led to an increase in cariprazine AUC (0 to 24 hours) and Cmax by roughly 50% 1. In one study that enrolled only White males taking cariprazine 1.5 mg/day and erythromycin 500 mg twice daily (n=40), AUCs rose by 38% (cariprazine), 11% (desmethylcariprazine, an active metabolite), and 60% (didesmethylcariprazine, an active metabolite), and Cmax rose by 34%, 16%, and 62%, respectively. Tmax was not altered by coadministration with erythromycin 2.
Common questions
Can I take Letermovir and Cariprazine together?
Letermovir can raise cariprazine levels and side effects, so your care team will likely lower the cariprazine dose and monitor you while the two are combined. Keep taking both as prescribed and check with your pharmacist or doctor. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Letermovir and Cariprazine 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 Cariprazine interaction managed?
What your care team may do: Use a lower cariprazine dose while you are taking letermovir, since exposure to cariprazine and its active metabolite goes up. Watch you more closely for side effects like restlessness, drowsiness, or stiff or shaky movements. Re-adjust your cariprazine dose again if the letermovir is later stopped. What you should do: Keep taking both medicines exactly as prescribed un… 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.
Questions for your pharmacist
- Does my dose of Letermovir or Cariprazine 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: VRAYLAR(R) oral capsules, cariprazine oral capsules. AbbVie Inc. (per FDA), North Chicago, IL, 2024. DailyMed
- Szabo M, Hujber Z, Harsanyi J, et al: Coadministration of cariprazine with a moderate CYP3A4 inhibitor in patients with schizophrenia: implications for dose adjustment and safety monitoring. Clin Pharmacokinet 2024; 63(10):1501-1510. PubMed
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