Abemaciclib and Saquinavir: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 10, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Saquinavir
No brand names on recordAbemaciclib
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. Saquinavir slows down a liver enzyme (called CYP3A4) that normally helps your body break down abemaciclib (Verzenio). When that cleanup slows, more abemaciclib can build up in your blood.
That extra buildup can make abemaciclib's side effects stronger, like diarrhea, nausea, tiredness, or lower blood counts. The good news is this is very manageable. Your care team can simply lower your abemaciclib dose while you're on saquinavir, and raise it back later if saquinavir is stopped. Please don't change anything on your own. Just let your doctor or pharmacist know you take both so they can tailor your dose and keep an eye on you.
Mechanism: Saquinavir is a strong CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate. Inhibition reduces abemaciclib clearance, raising plasma exposure (AUC/Cmax) of abemaciclib and its active metabolites, increasing toxicity risk (diarrhea, neutropenia, hepatotoxicity, fatigue).
- Direction: increased abemaciclib effect/toxicity
- Evidence: theoretical; onset: unspecified
- Management: If starting dose was 200 mg or 150 mg BID, reduce to 100 mg BID. If already reduced to 100 mg BID for adverse reactions, further reduce to 50 mg BID.
- On discontinuing saquinavir, after 3 to 5 inhibitor half-lives, resume the pre-inhibitor abemaciclib dose.
Monitor for abemaciclib-related toxicity and CBC/LFTs per protocol.
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
Taking abemaciclib together with a potent CYP3A4 inhibitor can raise plasma concentrations of both abemaciclib and its active metabolite, potentially heightening toxicity. When these agents are given together and the initial abemaciclib dose was either 200 mg or 150 mg twice daily, the abemaciclib dose should be lowered to 100 mg twice daily. For patients whose dose has already been decreased to 100 mg twice daily because of adverse reactions, a further reduction to 50 mg twice daily is warranted. Once the strong CYP3A inhibitor is stopped, the abemaciclib dose should be raised back to the level used prior to starting the strong inhibitor, doing so after 3-5 half-lives of the inhibitor have elapsed1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
What your care team may do:
- Lower your abemaciclib dose while you are also taking saquinavir. Per the guidance, a 200 mg or 150 mg twice-daily dose may be reduced to 100 mg twice daily, and if you were already at 100 mg twice daily for side effects, to 50 mg twice daily.
- Watch you more closely for side effects like diarrhea, fatigue, or blood count changes.
- Raise your abemaciclib dose back to the previous level after saquinavir has been stopped (allowing a few days for it to clear).
What you should do: Keep taking both exactly as prescribed and tell your pharmacist or oncologist you are on both so they can individualize your dose.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) Drug interaction studies predict that giving abemaciclib together with itraconazole (a strong CYP3A inhibitor) will raise the AUC of abemaciclib plus its active metabolites (M2, M18 and M20) by 2.2-fold 1.
b) In drug interaction studies conducted in cancer patients, administering a single 50 mg dose of abemaciclib (0.3 times the approved 150 mg dosage) alongside clarithromycin 500 mg twice daily (a strong CYP3A inhibitor) raised the AUC(0 to infinity) of abemaciclib plus its active metabolites (M2, M18, and M20) by 1.7-fold relative to abemaciclib given alone 1.
Common questions
Can I take Abemaciclib and Saquinavir together?
Saquinavir can raise abemaciclib levels and side effects by slowing its breakdown, but your oncology team can manage this by lowering the abemaciclib dose while you're on saquinavir and monitoring you more closely. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Saquinavir interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Abemaciclib and Saquinavir interaction managed?
What your care team may do: Lower your abemaciclib dose while you are also taking saquinavir. Per the guidance, a 200 mg or 150 mg twice-daily dose may be reduced to 100 mg twice daily, and if you were already at 100 mg twice daily for side effects, to 50 mg twice daily. Watch you more closely for side effects like diarrhea, fatigue, or blood count changes. Raise your abemaciclib dose back to the… 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 Abemaciclib or Saquinavir 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 anything you'd monitor while I'm on both?
References (1)
- Product Information: VERZENIO(TM) oral tablets, abemaciclib oral tablets. Lilly USA LLC (per FDA), Indianapolis, IN, 2017. DailyMed
Keep reading about Saquinavir
Keep reading about Abemaciclib
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