What the FDA labels say about taking them together
Phenobarbital and tacrolimus
Tacrolimus's FDA label of July 17, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name tacrolimus. The tacrolimus label: “Increase PROGRAF dose and monitor tacrolimus whole blood trough concentrations.”
Check it at the source: the phenobarbital FDA label on DailyMed (effective August 27, 2026); the tacrolimus FDA label on DailyMed (effective July 17, 2026, Stellon Biotech Inc.).
What does the phenobarbital label say about tacrolimus?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name tacrolimus in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), via openFDA; the full label on DailyMed
What does the tacrolimus label say about phenobarbital?
Tacrolimus label, drug interactionsDrug/Substance Class or Name: Strong CYP3A Inducers 3: Antimycobacterials (e.g., rifampin, rifabutin), anticonvulsants (e.g., phenytoin, carbamazepine and phenobarbital), St John's wort; Drug Interaction Effect: May decrease tacrolimus whole blood trough concentrations and increase the risk of rejection [see)].; Recommendations: Increase tacrolimus dose and monitor tacrolimus whole blood trough concentrations [ see,) and ].
Prograf label (Astellas Pharma US, Inc., August 25, 2023), drug interactionsDrug/Substance Class or Name: Strong CYP3A Inducers Strong CYP3A inhibitor/inducer, based on reported effect on exposures to tacrolimus along with supporting in vitro CYP3A inhibitor/inducer data, or based on drug-drug interaction studies with midazolam (sensitive CYP3A probe substrate).: Antimycobacterials (e.g., rifampin, rifabutin), anticonvulsants (e.g., phenytoin, carbamazepine and phenobarbital), St John’s wort; Drug Interaction Effect: May decrease tacrolimus whole blood trough concentrations and increase the risk of rejection [see ()].; Recommendations: Increase PROGRAF dose and monitor tacrolimus whole blood trough concentrations [see (,) and ()].
Source: FDA drug label (Prograf, NDA050708), Astellas Pharma US, Inc., effective August 25, 2023 (SPL set 7f667de1-9dfa-4bd6-8ba0-15ee2d78873b), via openFDA
Source: FDA drug label (Astagraf Xl, NDA204096), Astellas Pharma US, Inc., effective January 14, 2026 (SPL set 550a5cd4-fbf2-4c09-b577-6bde8fcbdf6e), via openFDA
Source: FDA drug label (Envarsus Xr, NDA206406), Veloxis Pharmaceuticals, Inc, effective February 26, 2025 (SPL set de2315b0-6344-43ac-9aea-3e3b68d828e7), via openFDA
Source: FDA drug label (Tacrolimus), Stellon Biotech Inc., effective July 17, 2026 (SPL set 6b89e8a4-9f11-42e3-8e79-fe617e7c461f), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Phenobarbital | Tacrolimus | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Organ transplant rejection, Eczema (atopic dermatitis) |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.213 per tablet 100 mg tablet | $0.970 per gram 0.1% ointment |
| Shortage now | A presentation being discontinued | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once