What the FDA labels say about taking them together
Atazanavir and phenytoin
Atazanavir's FDA label of August 6, 2025 names phenytoin in its contraindications section; the phenytoin labels PlainMeds reads (2) do not name atazanavir. The atazanavir label: “Coadministration of REYATAZ with phenytoin or phenobarbital is contraindicated due to the risk for loss of virologic response and development of resistance.”
Check it at the source: the atazanavir FDA label on DailyMed (effective August 6, 2025, Aurobindo Pharma Limited); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the atazanavir label say about phenytoin?
Atazanavir label, contraindicationsDrug Class: Anticonvulsants; Drugs within class that are contraindicated with atazanavir capsules: Carbamazepine, phenobarbital, phenytoin
Atazanavir label, drug interactionsConcomitant Drug Class/Specific Drugs: phenytoin, phenobarbital; Effect on Concentration of Atazanavir or Concomitant Drug: ↓ atazanavir ↓ phenytoin ↓ phenobarbital; Clinical Comment: Coadministration of atazanavir (with or without ritonavir) with phenytoin or phenobarbital is contraindicated due to the risk for loss of virologic response and development of resistance [see ].
Source: FDA drug label (Reyataz, NDA021567), E.R. Squibb & Sons, L.L.C., effective December 5, 2024 (SPL set 165cff62-b284-4a27-a65d-9ec8a5bfcdd8), via openFDA
Source: FDA drug label (Atazanavir Sulfate), Aurobindo Pharma Limited, effective August 6, 2025 (SPL set 7fbea274-d6b5-4faa-bbf0-05fefab42114), via openFDA; the full label on DailyMed
What does the phenytoin label say about atazanavir?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name atazanavir 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
| Atazanavir | Phenytoin | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $2.23 per capsule 300 mg capsule | $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