What the FDA labels say about taking them together
Atazanavir and phenobarbital
Atazanavir's FDA label of August 6, 2025 names phenobarbital in its contraindications section; the phenobarbital 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 phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the atazanavir label say about phenobarbital?
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 phenobarbital label say about atazanavir?
Phenobarbital's label (effective August 27, 2026) 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 (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), 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 | Phenobarbital | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $2.23 per capsule 300 mg capsule | $0.213 per tablet 100 mg tablet |
| Shortage now | No current entry | A presentation being discontinued |
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