Fosamprenavir 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
Fosamprenavir
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.
Here's what's going on. Cariprazine (Vraylar) is broken down by a liver enzyme called CYP3A4. Fosamprenavir (Lexiva) slows that enzyme down, so cariprazine and its active breakdown product can build up higher than usual in your body. That could mean stronger side effects, like feeling restless, sleepy, dizzy, or having muscle stiffness or tremor.
The good news is this is very manageable. Your care team already has a clear plan for lowering the cariprazine dose when it's taken with a medicine like fosamprenavir. Please don't stop or change either medicine on your own. Just check in with your pharmacist or doctor so they can make sure your dose is right for you.
Mechanism: Cariprazine and its active metabolite DDCAR are CYP3A4 substrates. Fosamprenavir (via its active moiety amprenavir) is a moderate CYP3A4 inhibitor, so coadministration is expected to increase cariprazine/DDCAR exposure (higher AUC/Cmax).
Direction: Increased cariprazine effect and dose-related adverse effects (akathisia, EPS, sedation).
Evidence/onset: Theoretical; onset unspecified. Severity major.
Management:
- Follow labeled dose reductions for concomitant moderate CYP3A4 inhibitor (e.g., 1.5 mg every other day up to individualized targets depending on indication and current dose).
- Monitor for EPS, akathisia, and sedation.
- Re-increase cariprazine dose when the inhibitor is discontinued, per clinical response.
What happens
Increased cariprazine and its major active metabolite (didesmethylcariprazine (DDCAR)) exposure
Interaction Deep Dive
Giving cariprazine (a CYP3A4 substrate) together with a moderate CYP3A4 inhibitor can raise 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, guided by clinical response and tolerability. For bipolar depression or as adjunctive treatment of major depressive disorder (MDD) in a patient on a moderate CYP3A4 inhibitor, use 1.5 mg orally every other day. If instead a moderate CYP3A4 inhibitor is being added to an established cariprazine regimen: for patients currently receiving 1.5 or 3 mg once daily, reduce cariprazine to 1.5 mg orally every other day when the inhibitor is started; for patients currently receiving 4.5 or 6 mg once daily, reduce cariprazine to 1.5 mg orally once daily when the inhibitor is started. Should the moderate CYP3A4 inhibitor be stopped, the cariprazine dose may require an increase according to clinical response and tolerability. The combined use of cariprazine (a CYP3A4 substrate) with a CYP3A4 inducer is also not advised. CYP3A4 governs both the formation and clearance of cariprazine's active metabolites. Because the impact of CYP3A4 inducers on cariprazine exposure has not been studied, the overall net effect remains unclear1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of cariprazine; induction of CYP3A4-mediated metabolism of cariprazine
How to manage this interaction
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. This interaction is well recognized and can be handled with dose planning.
- Your care team may lower your cariprazine dose (for example, taking it every other day rather than daily) while you are on fosamprenavir, and tailor it to your specific dose and diagnosis.
- They may watch you more closely for side effects like restlessness, muscle stiffness, tremor, or drowsiness.
- If fosamprenavir is later stopped, your cariprazine dose may need to be raised again based on how you respond.
What to do: Ask your pharmacist or doctor to confirm your cariprazine dose is adjusted for this combination.
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 over 21 days led to an increase in cariprazine AUC (0 to 24 hours) and Cmax of about 50% 1.
Common questions
Can I take Fosamprenavir and Cariprazine together?
Fosamprenavir can raise cariprazine levels and side effects, so your care team will likely reduce and individualize your cariprazine dose while watching for effects like restlessness, stiffness, or drowsiness. Keep taking both as prescribed and confirm the dosing with your pharmacist or doctor. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fosamprenavir 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 Fosamprenavir and Cariprazine interaction managed?
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. This interaction is well recognized and can be handled with dose planning. Your care team may lower your cariprazine dose (for example, taking it every other day rather than daily) while you are on fosamprenavir, and tailor it to your specific dose and diagnosis. They may watch you more closely for side effects li… 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.
Questions for your pharmacist
- Does my dose of Fosamprenavir 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 (1)
- Product Information: VRAYLAR(R) oral capsules, cariprazine oral capsules. AbbVie Inc. (per FDA), North Chicago, IL, 2024. DailyMed
Keep reading about Fosamprenavir
Keep reading about Cariprazine
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