Omeprazole and Nelfinavir: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Nelfinavir
Omeprazole
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.
These two medicines don't work well together. Nelfinavir (Viracept) is an HIV medicine that needs to stay at a steady level in your body to keep the virus under control. Omeprazole (Prilosec) is a common stomach acid reducer.
When they're taken together, the amount of nelfinavir in your blood can drop a lot. If your HIV medicine gets too low, it may stop working and the virus can become resistant, which is a real problem. That's why doctors usually avoid this combination. Please don't change anything on your own. Talk with your pharmacist or doctor, they can pick a safer stomach option or adjust your plan.
Direction: Coadministration is not recommended. Omeprazole (a CYP2C19 inhibitor) alters nelfinavir metabolism, and clinical data show a significant reduction in nelfinavir and active M8 metabolite exposure, risking loss of virologic control and resistance. Nelfinavir (CYP3A inhibitor) may also increase omeprazole exposure.
- Mechanism: CYP2C19/CYP3A-mediated interaction; net effect is reduced nelfinavir efficacy despite variable PK changes.
- Evidence: Established (open-label, single-sequence study, n=20).
- Management: Avoid concurrent use. Consider an alternative acid-suppression strategy or alternative antiretroviral regimen; individualized selection by the care team.
What happens
Increased omeprazole exposure, altered nelfinavir exposure and reduced efficacy of nelfinavir
Interaction Deep Dive
When nelfinavir is taken together with omeprazole (a CYP3A substrate), exposure to omeprazole may rise. Likewise, giving nelfinavir alongside omeprazole (a CYP2C19 inhibitor) may raise nelfinavir exposure 2. Because there is a risk that nelfinavir exposure could be substantially lowered, potentially leading to loss of therapeutic effect and the emergence of resistance, the combination of nelfinavir and omeprazole is not advised 21. In an open-label, two-period, single-fixed sequence study involving 20 subjects, giving nelfinavir with omeprazole markedly decreased the systemic exposure of both nelfinavir and its active metabolite, M8 3.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of omeprazole; inhibition of CYP2C19-mediated metabolism of nelfinavir
How to manage this interaction
The main goal is protecting your HIV treatment. Because this pairing can lower nelfinavir levels, the usual approach is to avoid using them together.
- Keep taking both medicines as prescribed until you speak with your care team, do not stop on your own.
- Your team may switch you to a different stomach acid medicine, or adjust your regimen, tailored to you.
- Tell your prescriber or pharmacist about any over-the-counter Prilosec, since it's sold without a prescription.
- Mention any heartburn or reflux so they can find a compatible option.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) Giving nelfinavir together with omeprazole appeared to markedly lower the systemic exposure to nelfinavir and to its active metabolite, M8. In an open-label study using two periods and a single fixed sequence, 20 participants (aged 18 to 48 years) took nelfinavir 1250 mg every 12 hours on days 1 through 3 and 1250 mg on the morning of day 4 (period 1). After a 7 day washout, participants took omeprazole 40 mg every 24 hours along with nelfinavir 1250 mg every 12 hours for 3 days, plus omeprazole 40 mg with nelfinavir 1250 mg on the morning of day 4 (period 2). Analysis of plasma samples demonstrated reductions of 36%, 37%, and 39% in nelfinavir Cmax, AUC, and Cmin, respectively, versus nelfinavir given alone. Furthermore, measurement of the M8 metabolite revealed decreases of 92% (Cmax), 89% (AUC), and 75% (Cmin) 31.
b) In a retrospective cohort study involving adult HIV-positive patients who filled at least 2 prescriptions for nelfinavir, an intent-to-treat (ITT)-like analysis showed a heightened risk of virologic rebound among patients who also had proton-pump inhibitor (PPI) exposure, especially long-term exposure, relative to those without such exposure; nevertheless, an as-treated analysis identified no meaningful difference in virologic rebound between the 2 groups. Patients were tracked until nelfinavir was stopped, an insurance gap of 3 or more months occurred, a nelfinavir refill was delayed by more than 30 days, the primary endpoint was reached, or the study ended. The ITT-like analysis presumed ongoing PPI use once it was prescribed, while in the as-treated analysis patients were counted as PPI-exposed only up to 30 days after the last expected PPI refill was projected to be depleted. Neither analysis showed a meaningful difference in the time to reaching virologic undetectability. However, the adjusted ITT-like findings indicated an elevated risk of virologic rebound in nelfinavir-treated patients with PPI exposure compared with those without PPI exposure (hazard ratio (HR), 1.53; 95% CI, 1.06 to 2.19). When the data were stratified by duration of PPI exposure, a 56% increased risk of virologic rebound emerged (HR, 1.56; 95% CI, 1.08 to 2.26; p=0.02) with long-term exposure (30 days or greater) but not with short-term exposure (less than 30 days); this increased risk, however, was not significant in the as-treated analysis 4.
Common questions
Can I take Omeprazole and Nelfinavir together?
Taking omeprazole with nelfinavir can significantly lower your HIV medicine and let the virus become resistant, so this combination is generally avoided. Ask your pharmacist or doctor about a safer acid-reducing option. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Omeprazole and Nelfinavir 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 is the Omeprazole and Nelfinavir interaction managed?
The main goal is protecting your HIV treatment. Because this pairing can lower nelfinavir levels, the usual approach is to avoid using them together. Keep taking both medicines as prescribed until you speak with your care team, do not stop on your own. Your team may switch you to a different stomach acid medicine, or adjust your regimen, tailored to you. Tell your prescriber or pharmacist about an… Management is individual — always follow your own care team's guidance.
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 Omeprazole or Nelfinavir 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 (4)
- Product Information: KONVOMEP(TM) powder for oral suspension, omeprazole sodium bicarbonate powder for oral suspension. Azurity Pharmaceuticals Inc (per manufacturer), Woburn, MA, 2022. DailyMed
- Product Information: VIRACEPT(R) oral film coated tablets, oral powder, nelfinavir mesylate oral film coated tablets, oral powder. Pfizer Inc (per Dailymed), New York, NY, 2023. DailyMed
- Fang AF, Damle BD, LaBadie RR, et al: Significant decrease in nelfinavir systemic exposure after omeprazole coadministration in healthy subjects. Pharmacotherapy 2008; 28(1):42-50. PubMed
- Saberi P, Ranatunga DK, Quesenberry CP, et al: Clinical implications of the nelfinavir-proton pump inhibitor drug interaction in patients with human immunodeficiency virus. Pharmacotherapy 2011; 31(3):253-261. PubMed
Keep reading about Nelfinavir
Keep reading about Omeprazole
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