Famotidine and Amprenavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Amprenavir
No brand names on recordFamotidine
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
Decreased fosamprenavir absorption and reduction of amprenavir efficacy (active fosamprenavir metabolite)
Interaction Deep Dive
Concomitant use of fosamprenavir and famotidine is not recommended due to the risk of reduced fosamprenavir absorption, which is dependent on gastric pH and may reduce the efficacy of amprenavir1, the active metabolite of fosamprenavir 2. In a study, when the gastric pH was raised with ranitidine, the concomitant use of fosamprenavir resulted in a decrease in amprenavir AUC of 30% and Cmax of 51% 3.
Why it happens (mechanism)
Increase in gastric pH
Literature reports
1 report — tap to read
a) Pharmacokinetic parameters (AUC and Cmax) of amprenavir decreased significantly in healthy adult patients treated with concomitant fosamprenavir and ranitidine, a histamine H2-receptor antagonist, compared to those treated with fosamprenavir only in a single-dose, randomized, cross-over study (N=26). Fosamprenavir 1400 mg was administered followed by a 4- to 7-day washout period. Then, fosamprenavir 1400 mg was administered 1 hour after ranitidine 300 mg. Compared to fosamprenavir alone, fosamprenavir plus ranitidine resulted in a decrease in amprenavir AUC of 30% and a decrease in amprenavir Cmax of 51% 3.
Common questions
Can I take Famotidine and Amprenavir together?
Decreased fosamprenavir absorption and reduction of amprenavir efficacy (active fosamprenavir metabolite) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Famotidine and Amprenavir 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 strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Famotidine or Amprenavir 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 (3)
- Product Information: DUEXIS oral tablets, ibuprofen famotidine oral tablets. Horizon Pharma USA, Inc. (per FDA), Lake Forest, IL, 2017. DailyMed
- Product Information: LEXIVA(R) oral solution, oral tablets, fosamprenavir calcium oral solution, oral tablets. GlaxoSmithKline, Research Triangle Park, NC, 2009. DailyMed
- Ford SL, Wire MB, Lou Y, et al: Effect of antacids and ranitidine on the single-dose pharmacokinetics of fosamprenavir. Antimicrob Agents Chemother 2005; 49(1):467-469. PubMed
Keep reading about Amprenavir
Keep reading about Famotidine
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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