Ketoconazole Topical and Telithromycin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Telithromycin
No brand names on recordKetoconazole Topical
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 telithromycin exposure, an increased ketoconazole exposure and an increased risk for QT interval prolongation
Interaction Deep Dive
Coadministration of ketoconazole, a strong CYP3A4 inhibitor that are known to prolong QT interval and CYP3A4 substrates that are known to prolong QT interval, such as telithromycin is contraindicated, as concomitant use may increase telithromycin exposure resulting in ventricular tachyarrhythmias, torsades de pointes, or potentially fatal arrhythmias. Concomitant use of ketoconazole (CYP3A4 substrate) with telithromycin (CYP3A4 inhibitor) may also increase ketoconazole exposure. If concomitant use is required, monitor the patient for signs and symptoms of increased or prolonged pharmacologic effects of ketoconazole. A multi-dose interaction study of the concomitant use of telithromycin and ketoconazole demonstrated an increase in the telithromycin Cmax and AUC of 51% and 95% respectively1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of telithromycin; inhibition of CYP3A4-mediated metabolism of ketoconazole; additive QT interval prolongation
Literature reports
2 reports — tap to read
a) A study of 12 patients age 60 and younger with impaired renal function reported the effects of coadministration of ketoconazole and telithromycin. When severe renal insufficiency and concomitant impairment of CYP3A4 metabolism pathway was evident, telithromycin exposure (AUC (0-24)) was increased nearly 4 to 5 fold compared with healthy subjects with normal function receiving telithromycin alone 2.
b) A multi-dose interaction study of the concomitant use of telithromycin and ketoconazole demonstrated an increase in the telithromycin Cmax and AUC of 51% and 95% respectively 12.
Common questions
Can I take Ketoconazole Topical and Telithromycin together?
Increased telithromycin exposure, an increased ketoconazole exposure and an increased risk for QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ketoconazole Topical and Telithromycin interaction?
It is rated contraindicated. These should generally not be used together.
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.
Questions for your pharmacist
- Does my dose of Ketoconazole Topical or Telithromycin 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 (2)
Keep reading about Telithromycin
Keep reading about Ketoconazole Topical
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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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