Tobramycin and Cefotaxime Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cefotaxime Injection
Tobramycin
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 plasma phosphorus
Interaction Deep Dive
The addition of cefotaxime and its metabolite to the serum of patients who had received gentamicin or tobramycin caused significant increases in phosphorus concentration1. When high and low concentrations of gentamicin or tobramycin were averaged together and compared to controls, the phosphorus level was approximately 1 mg/dL higher with the aminoglycoside. It is not known if this is the result of direct assay interference or a physicochemical interaction. The phosphorus assay method was the phosphomolybdate reaction with polyvinylpyrrolidone. The clinical importance of the increase in phosphorus is unknown.
Why it happens (mechanism)
Unknown
Common questions
Can I take Tobramycin and Cefotaxime Injection together?
Increased plasma phosphorus Always confirm with your pharmacist or prescriber before making any change.
How serious is the Tobramycin and Cefotaxime Injection interaction?
It is rated minor. Usually limited clinical impact.
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.
Questions for your pharmacist
- Does my dose of Tobramycin or Cefotaxime Injection 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 (1)
- Baer DM, Jones RN, Mullooly JP, et al: Protocol for the study of drug interference in 24 clinical tests. Clin Chem 1983; 29:1736-1740.
Keep reading about Cefotaxime Injection
Keep reading about Tobramycin
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