What the FDA labels say about taking them together
Lenacapavir and phenytoin
Lenacapavir's FDA label of August 27, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name lenacapavir. The lenacapavir label: “Concomitant administration of carbamazepine, oxcarbazepine, phenobarbital, or phenytoin may result in loss of therapeutic effect and development of resistance. …”
Check it at the source: the lenacapavir FDA label on DailyMed (effective August 27, 2026, Gilead Sciences, Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the lenacapavir label say about phenytoin?
Lenacapavir label, drug interactionsConcomitant Drug Class/Drug Name: Anticonvulsants: carbamazepine oxcarbazepine phenobarbital phenytoin; Effect on Concentration ↑ = Increase, ↓ = Decrease.: ↓ lenacapavir; Clinical Comment: Concomitant administration of carbamazepine, oxcarbazepine, phenobarbital, or phenytoin may result in loss of therapeutic effect and development of resistance. Concomitant administration of SUNLENCA with carbamazepine or phenytoin is contraindicated. Concomitant administration of SUNLENCA with oxcarbazepine or phenobarbital is not recommended. Consider use of alternative anticonvulsants.
Source: FDA drug label (Sunlenca), Gilead Sciences, Inc., effective August 27, 2026 (SPL set e5652804-29c4-40d7-aeb2-0142ed2a7b5b), via openFDA; the full label on DailyMed
What does the phenytoin label say about lenacapavir?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name lenacapavir 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
| Lenacapavir | Phenytoin | |
|---|---|---|
| Labeled for | HIV | 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