Lefamulin and Nelfinavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Nelfinavir
Lefamulin
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
Increased lefamulin exposure, an increased risk of lefamulin-related adverse reactions and an increased risk of QT interval prolongation
Interaction Deep Dive
Avoid concomitant use of lefamulin with strong CYP3A inhibitors or P-gp inhibitors that prolong the QT interval as it may increase lefamulin exposure and may increase the risk of adverse reactions with lefamulin, including QT prolongation. Lefamulin (oral or IV) has the potential to prolong the QT interval in some patients. The pharmacodynamic interaction potential to prolong the QT interval of the electrocardiogram between lefamulin and other drugs that effect cardiac conduction is unknown. ECG monitoring is recommended if coadministration cannot be avoided. The magnitude of QT prolongation may increase with increasing concentration of lefamulin or increasing the rate of infusion of the IV formulation. Therefore, do not exceed recommended dose and infusion rate. In a drug interaction study, oral ketoconazole (a strong CYP3A/P-gp inhibitor) increased the mean lefamulin AUC and Cmax by 31% and 6%, respectively, when administered concomitantly with IV lefamulin. Additionally, oral ketoconazole (strong inhibitor) increased the lefamulin AUC and Cmax by 165% and 58%, respectively, when administered concomitantly with oral lefamulin1.
Why it happens (mechanism)
Inhibition of P-gp-mediated efflux transport of lefamulin; inhibition of CYP3A4-mediated metabolism of lefamulin; additive QT prolongation
Literature reports
1 report — tap to read
a) In a drug interaction study, oral ketoconazole (a strong CYP3A/P-gp inhibitor) increased the mean lefamulin AUC(0 to infinity) and Cmax by 31% and 6%, respectively, when administered concomitantly with IV lefamulin. Additionally, oral ketoconazole (strong inhibitor) increased the lefamulin AUC(0 to inf) and Cmax by 165% and 58%, respectively, when administered concomitantly with oral lefamulin 1.
Common questions
Can I take Lefamulin and Nelfinavir together?
Increased lefamulin exposure, an increased risk of lefamulin-related adverse reactions and an increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Lefamulin 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 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 Lefamulin 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 (1)
- Product Information: XENLETA(R) oral tablets, intravenous injection, lefamulin oral tablets, intravenous injection. Nabriva Therapeutics US Inc (per FDA), King of Prussia, PA, 2021. DailyMed
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