Nizatidine and Atazanavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Atazanavir
Nizatidine
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
Interaction Deep Dive
Concomitant use of atazanavir (alone or with ritonavir) and an H2-blocker, may result in the loss of atazanavir efficacy and development of resistance. Although the interaction between atazanavir and nizatidine has not been studied, concomitant use of atazanavir and famotidine, another H2-receptor antagonist, has resulted in reduced atazanavir exposure. In treatment-naive patients, the nizatidine dose should not exceed a dose equivalent to famotidine 40 mg twice daily and the atazanavir 300 mg/ritonavir 100 mg dose (as a single dose with food) should be given with or at least 10 hours after the nizatidine dose. When atazanavir is given without ritonavir, the nizatidine dose should not exceed a dose equivalent to famotidine 20 mg/dose or 40 mg/daily and atazanavir 400 mg (once daily with food) should be given with or at least 2 hrs before and at least 10 hrs after nizatidine dose. In treatment-experienced patients, the nizatidine dose should not exceed a dose equivalent to famotidine 20 mg twice daily, and the atazanavir 300 mg/ritonavir 100 mg dose (single dose with food) should be given with or at least 10 hours after nizatidine dose. When used together with both tenofovir and nizatidine, atazanavir and ritonavir doses should be 400 mg and 100 mg, respectively (as a single dose with food). For treatment-experienced pregnant women during the second or third trimester, use atazanavir 400 mg and ritonavir 100 mg once daily when given with either tenofovir disoproxil fumarate or an H2-receptor antagonist. Atazanavir is not recommended with both tenofovir and an H2-receptor antagonist in this population1.
Why it happens (mechanism)
Reduced solubility of atazanavir as pH increases
Literature reports
3 reports — tap to read
a) 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% (90% confidence interval (CI), 18% to 66%), 41% (90% CI, 13% to 60%), and 42% (90% CI, 11% to 63%), respectively. However, when atazanavir 400 mg once daily was administered 10 hrs after and 2 hrs before famotidine 40 mg twice daily (n=14), the Cmax, AUC, and Cmin values were not significantly altered (8% increase (90% CI, 18% decrease to 41% increase), 5% decrease (90% CI, 26% decrease to 21% increase), and 21% decrease (90% CI 40% decrease to 4% increase), respectively 1.
b) 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 significant change in atazanavir geometric mean Cmax and a 1.79- and 4.46-fold higher AUC and minimum concentration (Cmin), respectively, 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 (2% increase (90% confidence interval (CI), 13% decrease to 18% increase), 3% increase (90% CI, 14% decrease to 22% increase), and 14% decrease (90% CI ,32% decrease to 8% increase)), respectively 1.
c) In study 1 (n=18), concomitant administration 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% (90% confidence interval (CI), 1% to 16%), 10% (90% CI, 2% to 18%), and 19% (90% CI, 6% to 31%), respectively. In study 2 (n=20), atazanavir 300 mg/ritonavir 100 mg/tenofovir 300 mg once daily administered 12 hrs after the evening famotidine 40 mg once-daily dose resulted in a decrease in atazanavir Cmax, AUC, and Cmin by 11% (90% CI, 3% to 19%), 12% (95% CI, 4% to 20%), and 23% (90% CI, 7% to 37%), respectively. In study 3 (n=18), atazanavir 300 mg/ritonavir 100 mg/tenofovir 300 mg once daily administered 10 hrs after the evening famotidine 40 mg dose and 2 hrs before the morning famotidine 40 mg dose resulted in a decrease in atazanavir Cmax, AUC, and Cmin by 26% (90% CI, 16% to 34%), 21% (90% CI, 12% to 30%), and 28% (90% CI, 17% to 37%), respectively 1.
Common questions
Can I take Nizatidine and Atazanavir together?
Reduced atazanavir exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Nizatidine and Atazanavir 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.
Questions for your pharmacist
- Does my dose of Nizatidine or Atazanavir 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: REYATAZ(R) oral capsules, oral powder, atazanavir oral capsules, oral powder. Bristol-Myers Squibb Company (per FDA), Princeton, NJ, 2020. DailyMed
Keep reading about Atazanavir
Keep reading about Nizatidine
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