What the FDA labels say about taking them together
Ensitrelvir and phenytoin
Ensitrelvir's FDA label of June 3, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name ensitrelvir. The ensitrelvir label: “Co-administration is contraindicated due to potential loss of virologic response.”
Check it at the source: the ensitrelvir FDA label on DailyMed (effective June 3, 2026, Shionogi Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the ensitrelvir label say about phenytoin?
Ensitrelvir label, drug interactionsDrug Class: Anticonvulsants; Drug (s) within Class: carbamazepine See, phenytoin; Effect on Drug Concentration: ↓ ensitrelvir; Clinical Comment: Co-administration is contraindicated due to potential loss of virologic response.
Source: FDA drug label (XOCOVA), Shionogi Inc., effective June 3, 2026 (SPL set 526acf60-abc3-2cc2-e063-6294a90affa6), via openFDA; the full label on DailyMed
What does the phenytoin label say about ensitrelvir?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name ensitrelvir 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
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
| Ensitrelvir | Phenytoin | |
|---|---|---|
| Labeled for | COVID-19 | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.145 per capsule 100 mg capsule |
| 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