Does Phenytoin Interact With Tacrolimus?

Name: Does Phenytoin Interact With Tacrolimus?
Creator: OmniRx Health

: Antimycobacterials (e.g., rifampin, rifabutin), anticonvulsants (e.g., phenytoin, carbamazepine and phenobarbital), St John’s wort May decrease tacrolimus whole blood trough concentrations and increase the risk of rejection [see Warnings and Precautions ( 5.10 )] .

Reviewed by the OmniRx Health clinical team•Last reviewed Jul 4, 2026

Severity: Moderate

Severity basis: drug interactions section (keywords: caution, may decrease). Combining Phenytoin (Anticonvulsant) and Tacrolimus (Calcineurin inhibitor immunosuppressant) is classified as a moderate interaction.

What to Do

Use this combination with caution. Your prescriber may monitor you more closely or adjust doses.

How This Interaction Works

Interactions like this one can happen when two medicines have overlapping effects, or when one changes how the other is absorbed, broken down, or cleared from the body. Phenytoin is a anticonvulsant and Tacrolimus is a calcineurin inhibitor immunosuppressant; together they are documented as a moderate interaction. How much this matters depends on your dose, your other medications, and your overall health.

If You Take Both Medications

If you have been prescribed both Phenytoin and Tacrolimus, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.

From the FDA Label

: Antimycobacterials (e.g., rifampin, rifabutin), anticonvulsants (e.g., phenytoin, carbamazepine and phenobarbital), St John’s wort May decrease tacrolimus whole blood trough concentrations and increase the risk of rejection [see Warnings and Precautions ( 5.10 )] .

Source: FDA structured product labeling (set_id 08cf2861-2483-405d-a872-a88a5c235f9a).

Phenytoin

Anticonvulsant

Brands: Dilantin

View Phenytoin safety profile

Tacrolimus

Calcineurin inhibitor immunosuppressant

Brands: Prograf, Astagraf XL

View Tacrolimus safety profile

Check these against your full medication list in our free Interaction Checker

Frequently Asked Questions

Can you take Phenytoin and Tacrolimus together?

Phenytoin and Tacrolimus have a documented moderate interaction. Use this combination with caution. Your prescriber may monitor you more closely or adjust doses.

How serious is the Phenytoin and Tacrolimus interaction?

It is classified as a moderate interaction, based on the FDA label's drug interactions section (keywords: caution, may decrease). A moderate interaction can be clinically meaningful and usually calls for monitoring or a dose adjustment.

What should I do if I'm taking both Phenytoin and Tacrolimus?

This information is educational — not medical advice.

This page is provided for general educational purposes and summarizes publicly available data from sources such as the U.S. Food & Drug Administration. It is not a substitute for the judgment of a licensed clinician and should not be used to start, stop, or change any medication. It may be incomplete or out of date, and individual circumstances vary. Always talk with your prescriber or pharmacist about your specific medications and health conditions. If you think you may have a medical emergency, call 911.

Questions About Your Medications?

A licensed OmniRx provider can review your full medication list and help you understand what's safe for you — no office visit required.

Other Phenytoin Interactions

Other Tacrolimus Interactions

Sources & References

Learn more about where our data comes from and how we write and review medical content.