Drug Interaction Report

Docetaxel Injection and Phenytoin: Interaction Details

A pharmacist-reviewed analysis of the Docetaxel Injection and Phenytoin interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Phenytoin

Dilantin Phenytek
+

Docetaxel Injection

Beizray Docefrez® Docivyx Taxotere®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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.

Of 122 documented Docetaxel Injection interactions, 99 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
probable
Severity
Major

What happens

Reduced docetaxel exposure

Interaction Deep Dive

The coadministration of docetaxel, a CYP3A substrate, with a strong CYP3A inducer may reduce docetaxel concentrations and efficacy12. In a physiologically-based pharmacokinetic (PBPK) model study, docetaxel AUC was predicted to decrease 16% when docetaxel 135 mg was coadministered with rifampicin 600 mg once daily (strong CYP3A inducer). Avoid concomitant use of docetaxel with strong CYP3A inducers if possible, as docetaxel has a narrow therapeutic index. If coadministration is required, monitor closely and adjust docetaxel dose if necessary 2.

Why it happens (mechanism)

Induction of CYP3A-mediated metabolism of docetaxel

Literature reports

1 report — tap to read

a) In a physiologically-based pharmacokinetic (PBPK) model study, docetaxel AUC was predicted to decrease 16% when docetaxel 135 mg was coadministered with rifampicin 600 mg once daily (strong CYP3A inducer). The study authors recommend avoiding coadministration of docetaxel with strong CYP3A inducers, and adjusting dosages as appropriate if coadministration is necessary 2.

Common questions

Can I take Docetaxel Injection and Phenytoin together?

Reduced docetaxel exposure Always confirm with your pharmacist or prescriber before making any change.

How serious is the Docetaxel Injection and Phenytoin 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 "probable". Good supporting evidence, though not definitively proven.

Questions for your pharmacist

  • Does my dose of Docetaxel Injection or Phenytoin 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)

  1. Product Information: DOCETAXEL anhydrous injection, docetaxel anhydrous injection. Sagent Pharmaceuticals (Per DailyMed), Schaumburg, IL, 2025. DailyMed
  2. Li T, Zhou S, Wang L, et al: Docetaxel, cyclophosphamide, and epirubicin: application of PBPK modeling to gain new insights for drug-drug interactions. J Pharmacokinet Pharmacodyn 2024; 51(4):367-384. PubMed
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Beyond drug–drug

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:

Phenytoin + 1,4-butanediol Activated Charcoal Beer Gamma-hydroxybutyrate (ghb) Kava L-tryptophan Siberian Cocklebur St. John's Wort + 216 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.