Drug Interaction Report

Dalteparin Injection and Warfarin: Interaction Details

A pharmacist-reviewed analysis of the Dalteparin Injection and Warfarin 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

Warfarin

Coumadin Jantoven
+

Dalteparin Injection

Fragmin Fragmin®
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 177 documented Dalteparin Injection interactions, 138 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
theoretical
Severity
Major

What happens

An increased risk of bleeding

Interaction Deep Dive

Use caution with the concomitant use of dalteparin with other anticoagulants, such as warfarin1, as it may increase the risk of bleeding due to additive anticoagulation 2. Coadministration of dalteparin and warfarin may also increase the risk of developing epidural or spinal hematomas in patients who are receiving neuraxial anesthesia or undergoing spinal puncture 1. When coadministration is required, more frequent monitoring of prothrombin time/INR is recommended, especially during initiation or discontinuation of dalteparin. Warfarin dose adjustment may be required to maintain desired levels. Increased prothrombin time/INR responses have been reported with concomitant use of warfarin and anticoagulants 3.

Why it happens (mechanism)

Additive anticoagulation

Common questions

Can I take Dalteparin Injection and Warfarin together?

An increased risk of bleeding Always confirm with your pharmacist or prescriber before making any change.

How serious is the Dalteparin Injection and Warfarin 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.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Dalteparin Injection or Warfarin 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 (3)

  1. Product Information: FRAGMIN(R) subcutaneous injection, dalteparin sodium subcutaneous injection. Pfizer Labs (per FDA), New York, NY, 2020. DailyMed
  2. Product Information: WARFARIN SODIUM oral tablets, warfarin sodium oral tablets. Teva Pharmaceuticals (per Dailymed), Parsippany, NJ, 2023. DailyMed
  3. Product Information: COUMADIN(R) oral tablets, intravenous injection, warfarin sodium oral tablets, intravenous injection. Bristol-Myers Squibb Company, Princeton, NJ, 2010. DailyMed
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Beyond drug–drug

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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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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.