Diazepam Rectal and Fosamprenavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Fosamprenavir
Diazepam Rectal
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.
What happens
An increased risk of diazepam toxicity (excessive sedation, confusion, respiratory depression)
Interaction Deep Dive
Plasma concentrations of diazepam may be elevated by the concurrent administration of fosamprenavir. Amprenavir, the active metabolite of fosamprenavir, and diazepam are both metabolized by CYP3A4 isoenzymes, and amprenavir is also an inhibitor of CYP3A4. Competition for metabolism and/or inhibition of metabolism could result in an increased plasma concentration of diazepam. Although clinical significance is unknown, a decrease in diazepam dosing may be warranted1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated diazepam metabolism by amprenavir, the active metabolite of fosamprenavir
Common questions
Can I take Diazepam Rectal and Fosamprenavir together?
An increased risk of diazepam toxicity (excessive sedation, confusion, respiratory depression) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Diazepam Rectal and Fosamprenavir 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 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 Diazepam Rectal or Fosamprenavir 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: LEXIVA(R) oral solution, oral tablets, fosamprenavir calcium oral solution, oral tablets. GlaxoSmithKline, Research Triangle Park, NC, 2009. DailyMed
Keep reading about Fosamprenavir
Keep reading about Diazepam Rectal
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