What the FDA labels say about taking them together
Darunavir and phenytoin
Darunavir's FDA label of August 29, 2025 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name darunavir. The darunavir label: “Phenytoin and phenobarbital levels should be monitored when co-administering with PREZISTA/ritonavir.”
Check it at the source: the darunavir FDA label on DailyMed (effective August 29, 2025, Janssen Products LP); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the darunavir label say about phenytoin?
Darunavir label, drug interactionsConcomitant Drug Class Drug Name Examples: phenobarbital, phenytoin; Effect on Concentration of Darunavir Or Concomitant Drug: ↔ darunavir ↓ phenytoin ↓ phenobarbital; Clinical Comment: Phenytoin and phenobarbital levels should be monitored when co-administering with PREZISTA/ritonavir.
Source: FDA drug label (PREZISTA), Janssen Products LP, effective August 29, 2025 (SPL set 814301f9-c990-46a5-b481-2879a521a16f), via openFDA; the full label on DailyMed
What does the phenytoin label say about darunavir?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name darunavir 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
| Darunavir | Phenytoin | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $1.16 per tablet 600 mg tablet | $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