Fosphenytoin and Apixaban: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Aug 8, 2026 · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Fosphenytoin
Apixaban
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.
Here's what's going on. Fosphenytoin (Cerebyx) is a seizure medicine that speeds up how fast your body breaks down and clears out other drugs. Apixaban (Eliquis) is a blood thinner that helps prevent dangerous clots and strokes. When you take them together, your body may clear the apixaban too quickly, so there may not be enough in your blood to protect you.
The concern is that the blood thinner could stop working as well, raising your risk of a clot or stroke. The good news is your care team knows how to handle this. Please don't stop or change either medicine on your own, but do talk with your doctor or pharmacist so they can review the best plan for you.
Effect: Fosphenytoin (prodrug of phenytoin) is a strong CYP3A4 and P-glycoprotein inducer. It increases apixaban clearance via induced CYP3A4-mediated metabolism and P-gp-mediated efflux, reducing apixaban exposure (AUC) and Cmax.
- Direction: reduced apixaban effect, increased risk of stroke/thromboembolism.
- Evidence: established; PK data with rifampin and a retrospective DOAC cohort (levels below 5th percentile in ~half of patients).
- Onset: unspecified (enzyme induction typically develops over days to weeks).
- Management: avoid the combination where possible. If coadministration is necessary, DOAC concentration monitoring may be useful, and therapy should be individualized by the care team.
What happens
Reduced apixaban exposure, reduced efficacy of apixaban and an increased risk of stroke and other thromboembolic events
Interaction Deep Dive
Do not combine apixaban with agents that act as both P-glycoprotein and strong CYP3A4 inducers, including rifAMPin, carBAMazepine, phenytoin, and St. John's Wort. In pharmacokinetic investigations, coadministration with rifAMPin reduced both apixaban exposure and Cmax 1. Additionally, a retrospective study found that among patients taking apixaban together with an enzyme-inducing agent, half had apixaban concentrations falling below the fifth percentile of anticipated values. When it becomes necessary to use a direct oral anticoagulant (DOAC) alongside an enzyme-inducing drug, checking the DOAC concentration may be helpful 5.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of apixaban; induction of P-gp-mediated efflux transport of apixaban
How to manage this interaction
What your care team may do:
- Generally avoid using apixaban with strong inducers like fosphenytoin when a good alternative exists.
- If both are truly needed, your team may check your apixaban blood levels and monitor you more closely, tailoring the plan to you.
- They may consider a different anticoagulant or a different seizure medicine, depending on your situation.
What you should do: keep taking both exactly as prescribed for now, and do not stop either one on your own. Reach out to your pharmacist or prescriber so they can review your regimen. Report any signs of a clot right away, such as sudden weakness, trouble speaking, chest pain, or leg swelling.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
6 reports — tap to read
a) A retrospective cohort study using propensity score matching in adults (n=14,078 eligible episodes) found no difference in the risk of thromboembolic events among patients taking direct-acting oral anticoagulant (DOAC) therapy (apixaban, dabigatran, or rivaroxaban) together with enzyme-inducing antiseizure medications (EI-ASMs), such as carbamazepine, oxcarbazepine, phenobarbital, phenytoin, primidone, or topiramate, versus those on non-EI-ASMs (adjusted HR, 1.1 [95% CI, 0.82 to 1.46]). A secondary analysis (n=14,158 eligible episodes) showed a significant decrease in major bleeding events when DOACs were used concurrently with EI-ASMs compared with non-EI-ASMs (adjusted HR, 0.63 [95% CI, 0.44 to 0.89]) 2.
b) A significantly higher risk of stroke/systemic embolism was observed when direct-acting oral anticoagulant (DOAC) drugs were given together with carBAMazepine (adjusted OR, 2.15; 95% CI, 1.07 to 4.3) or 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). The patients were new users of DOAC therapy, comprising 54.8% on apixaban, 31.3% on rivaroxaban, and 14% on dabigatran. The findings were adjusted for demographic and lifestyle variables 3.
c) In a prospective cohort study of patients with nonvalvular atrial fibrillation taking direct-acting oral anticoagulant therapy (DOAC) along with antiepileptic drugs (N=91), the combined outcome of ischemic stroke, transient ischemic attack, and systemic embolism occurred in 9 patients (5.7% patient-year; 3 fatalities) during a median follow-up of 17.5 +/- 14.5 months; however, patients who had a thromboembolic event were older (75 years or greater), had a prior stroke, and had a higher risk score (CHA(2)DS(2)-VASc greater than 3). While no direct comparisons were performed, this rate of thromboembolic events was reported as higher than rates seen in cohort studies of patients with atrial fibrillation treated with DOAC therapy alone. Major bleeding occurred in 3 patients (1.9% patient-year; 1 fatality). Within the study, 46.2%, 27.5%, 16.5%, and 9.9% of patients received apixaban, rivaroxaban, dabigatran, and edoxaban, respectively. Concurrent antiepileptic therapy included 45% on levETIRAcetam, 22% on valproic acid, 12% on PHENobarbital, 11% on carBAMazepine, and 10% on other antiepileptic therapy 4.
d) A retrospective study assessing hospitalized patients who received concurrent direct oral anticoagulants (DOACs; apixaban, 77%; rivaroxaban, 15%; dabigatran, 8%) with an enzyme-inducing drug (total study population, 1596; 22 [1.4%] received the concurrent prescriptions) found that a DOAC concentration below the fifth percentile of expected concentration occurred in 6 of 11 patients who had DOAC levels measured. Peak apixaban concentrations ranged from 35.8 to 205.4 mcg/L in 10 patients, versus a fifth percentile of 91 mcg/mL and a ninety-fifth percentile of 321 mcg/mL based on standard apixaban dosing from the ARISTOTLE study; 5 of the patients from the ARISTOTLE study had levels below the fifth percentile. The DOACs were prescribed for atrial fibrillation (86%) or VTE (14%), and the enzyme inducer was indicated mainly for seizure (55%), but also for neuropathy, essential tremor, or depression 5.
e) Mean apixaban Cmax fell by 42% and AUC(0 to infinity) fell by 54% when oral apixaban and oral rifAMPin were coadministered in healthy subjects (N=20). The oral bioavailability of apixaban decreased by 25% and the mean apparent clearance rose by 2.1-fold. Subjects received a single IV dose of apixaban 5 mg on Day 1 followed by a 10-mg oral dose on Day 3. RifAMPin 600 mg orally once daily was then given on Days 5 to 15. Finally, a single dose of apixaban 5 mg IV and 10 mg orally were given separately on Days 12 and 14 in randomized sequence 6.
f) In a drug interaction study, giving rifAMPin 600 mg together with apixaban led to reductions in apixaban Cmax and AUC of about 0.6-fold and 0.5-fold, respectively 1.
Common questions
Can I take Fosphenytoin and Apixaban together?
Fosphenytoin can make apixaban clear out too fast, weakening its clot protection and raising stroke risk. This combination is usually avoided, so check with your doctor or pharmacist before changing anything. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fosphenytoin and Apixaban 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 is the Fosphenytoin and Apixaban interaction managed?
What your care team may do: Generally avoid using apixaban with strong inducers like fosphenytoin when a good alternative exists. If both are truly needed, your team may check your apixaban blood levels and monitor you more closely, tailoring the plan to you. They may consider a different anticoagulant or a different seizure medicine, depending on your situation. What you should do: keep taking bo… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "established". Well documented — supported by controlled studies or strong clinical data.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Fosphenytoin or Apixaban 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 (6)
- Product Information: ELIQUIS(R) oral film coated tablets, apixaban oral film coated tablets. Bristol-Myers Squibb Company (per Dailymed), Princeton, NJ, 2024. DailyMed
- 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. DOI
- 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. PubMed
- Giustozzi M, Mazzetti M, Paciaroni M, et al: Concomitant use of direct oral anticoagulants and antiepileptic drugs: a prospective cohort study in patients with atrial fibrillation. Clin Drug Investig 2021; 41(1):43-51. DOI
- Perlman A, Hochberg-Klein S, Choshen Cohen L, et al: Management strategies of the interaction between direct oral anticoagulant and drug-metabolizing enzyme inducers. J Thromb Thrombolysis 2019; 47(4):590-595. PubMed
- Vakkalagadda B, Frost C, Byon W, et al: Effect of rifampin on the pharmacokinetics of apixaban, an oral direct inhibitor of Factor Xa. Am J Cardiovasc Drugs 2016; 16(2):119-127. PubMed
Keep reading about Fosphenytoin
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