Dabigatran and Phenytoin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenytoin
Dabigatran
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
Reduced dabigatran exposure
Interaction Deep Dive
Concurrent administration of phenytoin or fosphenytoin (prodrug of phenytoin) and dabigatran have resulted in reduced dabigatran exposure. Consider dabigatran dose adjustments to achieve optimal clinical response when phenytoin or fosphenytoin is added to or withdrawn from a patient's regimen456. Concomitant use of phenytoin or fosphenytoin, a combined P-gp and strong CYP3A4 inducer, and dabigatran may reduce dabigatran exposure 1 and increase the risk of thrombotic events. Therefore, avoid coadministration of phenytoin or fosphenytoin and dabigatran 7.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of dabigatran; induction of P-gp mediated efflux transport of dabigatran
Literature reports
3 reports — tap to read
a) There was no difference in the risk of thromboembolic events in a retrospective cohort study of propensity score-matched adults (n=14,078 eligible episodes) taking direct-acting oral anticoagulant (DOAC) therapy (apixaban, dabigatran, or rivaroxaban) concomitantly with enzyme-inducing antiseizure medications (EI-ASMs), including carBAMazepine, OXcarbazepine, PHENobarbital, phenytoin, primidone, or topiramate, compared with non-EI-ASMs (adjusted HR, 1.1 [95% CI, 0.82 to 1.46]). In a secondary analysis (n=14,158 eligible episodes), there was a significant reduction in major bleeding events with concomitant use of DOACs with EI-ASMs compared with non-EI-ASMs (adjusted HR, 0.63 [95% CI, 0.44 to 0.89]) 3.
b) A significantly increased risk of stroke/systemic embolism was noted with administration of direct-acting oral anticoagulant (DOAC) drugs concomitantly with phenytoin (OR, 4.46; 95% CI, 2.46 to 8.08) in a propensity-score adjusted nested case-control study of patients with atrial fibrillation or recent DVT/PE (N=89,284). Patients were new users of DOAC therapy and included 54.8% on apixaban, 31.3% on rivaroxaban, and 14% on dabigatran. Results were adjusted for demographic and lifestyle variables 8.
c) In a retrospective study (N=131) of patients receiving phenytoin (n=3) or other enzyme-inducing antiseizure medications (EI-ASM; n=22) concomitantly with direct oral anticoagulant (DOAC) therapy, 37.5% experienced DOAC concentrations below the therapeutic range compared with 9.3% who were not receiving phenytoin or other enzyme-inducing antiseizure medications (OR, 5.82; 95% CI, 2.03 to 16.66). Apixaban was used by 85% (111 patients) of patients within the study, however, some patients received rivaroxaban (14 patients) or dabigatran (6 patients) 2.
Common questions
Can I take Dabigatran and Phenytoin together?
Reduced dabigatran exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Dabigatran 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Dabigatran 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 (8)
- Steffel J, Collins R, Antz M, et al: 2021 European Heart Rhythm Association Practical Guide on the use of non-vitamin K antagonist oral anticoagulants in patients with atrial fibrillation. Europace 2021; 23(10):1612-1676.
- Perlman A, Goldstein R, Choshen Cohen L, et al: Effect of enzyme-inducing antiseizure medications on the risk of sub-therapeutic concentrations of direct oral anticoagulants: a retrospective cohort study. CNS Drugs 2021; 35(3):305-316. PubMed
- Acton EK, Hennessy S, Gelfand MA, et al: Direct-acting oral anticoagulants and antiseizure medications for atrial fibrillation and epilepsy and risk of thromboembolic events. JAMA Neurol 2024; Epub:Epub. PubMed
- Product Information: FOSPHENYTOIN SODIUM intravenous and intramuscular injection, fosphenytoin sodium intravenous and intramuscular injection. SAGENT Pharmaceuticals (per Dailymed), Schaumburg, IL, 2024. DailyMed
- Product Information: PHENYTOIN SODIUM intravenous and intramuscular injection, phenytoin sodium intravenous and intramuscular injection. Acella Pharmaceuticals, LLC (per Dailymed), Alpharetta, GA, 2024. DailyMed
- Product Information: PHENYTOIN SODIUM oral extended-release capsules, phenytoin sodium oral extended-release capsules. Sun Pharmaceutical Industries, Inc. (per Dailymed), Cranbury, NJ, 2023. DailyMed
- Mar PL, Gopinathannair R, Gengler BE, et al: Drug interactions affecting oral anticoagulant use. Circ Arrhythm Electrophysiol 2022; 15(6):e007956. PubMed
- Gronich N, Stein N, & Muszkat M: Association between use of pharmacokinetic-interacting drugs and effectiveness and safety of direct acting oral anticoagulants: nested case-control study. Clin Pharmacol Ther 2021; 110(6):1526-1536. DOI
Keep reading about Phenytoin
Keep reading about Dabigatran
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