Metronidazole and Cyclosporine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cyclosporine
Metronidazole
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
An increased risk of cycloSPORINE toxicity (nephrotoxicity, cholestasis, paresthesias)
Interaction Deep Dive
In a case report, the combined use of metronidazole 1500 mg daily and cimetidine 800 mg daily resulted in a greater than two-fold increase in cycloSPORINE levels (from 400 to 800 mcM/L). When cimetidine was discontinued, levels declined to about 600 mcM/L. It was not until metronidazole was discontinued that cycloSPORINE levels returned to baseline2. Another case report described a patient who experienced a 97% increase in his cycloSPORINE blood level when metronidazole 1200 mg daily was administered for one week 1.
Why it happens (mechanism)
Inhibition by metronidazole of cytochrome P450 3A4-mediate cycloSPORINE metabolism
Literature reports
1 report — tap to read
a) A 50-year-old male with a cadaveric renal allograft was stabilized on cycloSPORINE 125 mg twice daily with a trough cycloSPORINE concentration between 130 mcg/L and 150 mcg/L. Following a three-day history of vomiting and diarrhea, a stool culture isolated Campylobacter coli for which he was treated with metronidazole 400 mg three times daily for one week. His illness resolved over three days, but the cycloSPORINE level increased to 264 mcg/L and his serum creatinine increased from 0.17 mmol/L to 0.19 mmol/L. Following the discontinuation of metronidazole, cycloSPORINE levels decreased to 120 mcg/L and renal function returned to baseline 1.
Common questions
Can I take Metronidazole and Cyclosporine together?
An increased risk of cycloSPORINE toxicity (nephrotoxicity, cholestasis, paresthesias) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Metronidazole and Cyclosporine interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Metronidazole or Cyclosporine 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 anything you'd monitor while I'm on both?
References (2)
- Herzig K & Johnson DW: Marked elevation of blood cyclosporin and tacrolimus levels due to concurrent metronidazole therapy (letter). Nephrol Dial Transplant 1999; 14:521-523. PubMed
- Zylber-Katz E, Rubinger D, & Berlatzky Y: Cyclosporine interactions with metronizadole and cimetidine. DICP 1988; 22:504-505.
Keep reading about Cyclosporine
Keep reading about Metronidazole
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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