What the FDA labels say about taking them together
Phenytoin and tenofovir alafenamide
Tenofovir alafenamide's FDA label of July 14, 2025 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name tenofovir alafenamide. The tenofovir alafenamide label: “When coadministered with carbamazepine, the tenofovir alafenamide dose should be increased to two tablets once daily. Coadministration of VEMLIDY with oxcarbazepine, phenobarbital, or phenytoin is not recommended.”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the tenofovir alafenamide FDA label on DailyMed (effective July 14, 2025, Gilead Sciences, Inc.).
What does the phenytoin label say about tenofovir alafenamide?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name tenofovir alafenamide in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Phenytek), Mylan Pharmaceuticals Inc., effective October 15, 2024 (SPL set 0f94c791-8b07-4b41-927e-c9f28bec5f60), via openFDA; the full label on DailyMed
What does the tenofovir alafenamide label say about phenytoin?
Tenofovir alafenamide label, drug interactionsConcomitant Drug Class/Drug Name: Anticonvulsants:; Effect on Concentration ↓ = decrease.: ↓ tenofovir alafenamide; Clinical Comment: When coadministered with carbamazepine, the tenofovir alafenamide dose should be increased to two tablets once daily. Coadministration of VEMLIDY with oxcarbazepine, phenobarbital, or phenytoin is not recommended.
Source: FDA drug label (VEMLIDY), Gilead Sciences, Inc., effective July 14, 2025 (SPL set 72e6b33c-0351-4070-9172-eeaa186c01d2), 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
| Phenytoin | Tenofovir alafenamide | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Hepatitis B |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $51.98 per tablet 25 mg tablet |
| Shortage now | No current entry | 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