What the FDA labels say about taking them together
Phenytoin and sofosbuvir
Sofosbuvir's FDA label of December 26, 2024 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name sofosbuvir. The sofosbuvir label: “Coadministration of SOVALDI with carbamazepine, phenytoin, phenobarbital or oxcarbazepine is expected to decrease the concentration of sofosbuvir, leading to reduced therapeutic effect of SOVALDI. …”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the sofosbuvir FDA label on DailyMed (effective December 26, 2024, Gilead Sciences, Inc.).
What does the phenytoin label say about sofosbuvir?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name sofosbuvir 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 sofosbuvir label say about phenytoin?
Sofosbuvir label, drug interactionsConcomitant Drug Class/Drug Name: Anticonvulsants: Carbamazepine phenytoin phenobarbital oxcarbazepine; Effect on Concentration ↓ = decrease.: ↓ sofosbuvir ↓ GS-331007; Clinical Comment: Coadministration of SOVALDI with carbamazepine, phenytoin, phenobarbital or oxcarbazepine is expected to decrease the concentration of sofosbuvir, leading to reduced therapeutic effect of SOVALDI. Coadministration is not recommended.
Source: FDA drug label (Sovaldi), Gilead Sciences, Inc., effective December 26, 2024 (SPL set 80beab2c-396e-4a37-a4dc-40fdb62859cf), 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 | Sofosbuvir | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Hepatitis C |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | n/a |
| 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