Atazanavir and Famotidine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Atazanavir
Famotidine
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
Reduced atazanavir exposure and an increased risk of QT interval prolongation
Interaction Deep Dive
Concomitant use of atazanavir and famotidine resulted in reduced atazanavir exposure resulting in loss of atazanavir efficacy and development of resistance and may prolong the QT interval. For treatment-naive patients, do not exceed famotidine 40 mg twice daily and give atazanavir 300 mg/ritonavir 100 mg dose (single dose with food) with or at least 10 hours after the famotidine dose. When atazanavir is administered without ritonavir, do not exceed famotidine 20 mg/dose or 40 mg/day, and give atazanavir 400 mg (once daily with food) with or at least 2 hours before and at least 10 hours after the famotidine dose. For treatment-experienced patients, do not exceed famotidine 20 mg twice daily, and give atazanavir 300 mg/ritonavir 100 mg dose (single dose with food) with or at least 10 hours after famotidine dose. When used together with both tenofovir and famotidine, give atazanavir 400 mg/ritonavir 100 mg (as a single dose with food)1; or if using cobicistat, give atazanavir 400 mg/cobicistat 150 mg 2. For treatment-experienced pregnant women during second or third trimester, give atazanavir 400 mg/ritonavir 100 mg once daily when coadministered with either tenofovir disoproxil fumarate or famotidine; atazanavir is not recommended with both tenofovir and famotidine in this population 1.
Why it happens (mechanism)
Reduced solubility of atazanavir as pH increases; additive QT interval prolongation
Literature reports
4 reports — tap to read
a) In a multiple-dose, sequential study of patients with HIV (n=40) receiving atazanavir 300 mg/ritonavir 100 mg once daily plus 2 or more nucleoside reverse transcriptase inhibitors (with or without tenofovir), the Cmax, AUC, and Cmin of atazanavir significantly decreased following the addition of famotidine. Compared with those receiving atazanavir/ritonavir alone, the Cmax, AUC, and Cmin of atazanavir decreased by 23%, 23%, and 20%, respectively, in patients receiving atazanavir/ritonavir plus famotidine 40 mg twice daily and 20%, 13%, and 1%, respectively, in patients receiving atazanavir/ritonavir plus famotidine 20 mg twice daily. Compared with those receiving atazanavir/ritonavir/tenofovir alone, atazanavir Cmax, AUC, and Cmin decreased by 23%, 24%, and 25%, respectively, in patients receiving atazanavir/ritonavir/tenofovir plus famotidine 40 mg twice daily and 21%, 21%, and 19%, respectively, in patients receiving atazanavir/ritonavir/tenofovir plus famotidine 20 mg twice daily. There were no reports of serious adverse effects during the study and all patients maintained a virologically suppressed level of less than 400 copies/mL. The results confirmed the reduction in atazanavir exposure when administered with famotidine is similar in HIV-infected subjects compared with noninfected subjects 3.
b) When ritonavir was not part of the regimen, and famotidine and atazanavir were simultaneously administered, the Cmax, AUC, and minimum concentration (Cmin) of atazanavir were significantly decreased; however, the Cmax, AUC, and Cmin were not altered when atazanavir was administered 10 hours after or 2 hours before famotidine. Atazanavir 400 mg once daily administered simultaneously with famotidine 40 mg twice daily in 15 subjects resulted in a significant decline in atazanavir Cmax, AUC and Cmin by 47%, 41%, and 42%, respectively. However, when atazanavir 400 mg once daily was administered 10 hours after and 2 hours before famotidine 40 mg twice daily (n=14), the Cmax, AUC, and Cmin values were not significantly altered 1.
c) When ritonavir was part of the regimen, the Cmax was not altered when atazanavir/ritonavir was simultaneously coadministered with famotidine. Atazanavir 300 mg/ritonavir 100 mg once daily administered simultaneously with famotidine 40 mg twice daily in 14 subjects resulted in no change in mean atazanavir Cmax, a 1.79-fold higher AUC, and 4.46-fold higher minimum concentration (Cmin), relative to atazanavir 400 mg once daily without ritonavir. Furthermore, when atazanavir 400 mg/ritonavir 100 mg once daily was administered with famotidine 40 mg twice daily (n=15), the Cmax, AUC, and Cmin values were not significantly altered 1.
d) In study 1 (n=18), coadministration of famotidine 20 mg twice daily plus atazanavir 300 mg/ritonavir 100 mg/tenofovir 300 mg once daily (administered simultaneous with morning famotidine) resulted in a decrease in atazanavir Cmax, AUC, and minimum concentration (Cmin) by 9%, 10%, and 19%, respectively. In study 2 (n=20), atazanavir 300 mg/ritonavir 100 mg/tenofovir 300 mg once daily administered 12 hours after the evening famotidine 40-mg once-daily dose resulted in a decrease in atazanavir Cmax, AUC, and Cmin by 11%, 12%, and 23%, respectively. In study 3 (n=18), atazanavir 300 mg/ritonavir 100 mg/tenofovir 300 mg once daily administered 10 hours after the evening famotidine 40-mg dose and 2 hours before the morning famotidine 40 mg dose resulted in a decrease in atazanavir Cmax, AUC, and Cmin by 26%, 21%, and 28%, respectively 1.
Common questions
Can I take Atazanavir and Famotidine together?
Reduced atazanavir exposure and an increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Atazanavir and Famotidine 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 "established". Well documented — supported by controlled studies or strong clinical data.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Atazanavir or Famotidine 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: REYATAZ(R) oral capsules, oral powder, atazanavir oral capsules, oral powder. Bristol-Myers Squibb Company (per FDA), Princeton, NJ, 2020. DailyMed
- Product Information: TYBOST(R) oral tablets, cobicistat oral tablets. Gilead Sciences Inc (per manufacturer), Foster City, CA, 2020. DailyMed
- Wang X, Boffito M, Zhang J, et al: Effects of the H2-receptor antagonist famotidine on the pharmacokinetics of atazanavir-ritonavir with or without tenofovir in HIV-infected patients. AIDS Patient Care STDS 2011; 25(9):509-515.
Keep reading about Atazanavir
Keep reading about Famotidine
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
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