What the FDA labels say about taking them together
Atazanavir and fostamatinib
Atazanavir's FDA label of August 6, 2025 names fostamatinib in its drug interactions section; the fostamatinib label PlainMeds reads does not name atazanavir. The atazanavir label: “When coadministering fostamatinib with REYATAZ, monitor for toxicities of R406 exposure resulting in dose-related adverse events such as hepatotoxicity and neutropenia. Fostamatinib dose reduction may be required.”
Check it at the source: the atazanavir FDA label on DailyMed (effective August 6, 2025, Aurobindo Pharma Limited); the fostamatinib FDA label on DailyMed (effective November 5, 2025, Rigel Pharmaceuticals, Inc.).
What does the atazanavir label say about fostamatinib?
Atazanavir label, drug interactionsConcomitant Drug Class/Specific Drugs: Kinase inhibitors: fostamatinib; Effect on Concentration of Atazanavir or Concomitant Drug: ↑ R406 (active metabolite of fostamatinib); Clinical Comment: When coadministering fostamatinib with atazanavir (with or without ritonavir), monitor for toxicities of R406 exposure resulting in dose-related adverse events such as hepatotoxicity and neutropenia. Fostamatinib dose reduction may be required.
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 fostamatinib label say about atazanavir?
Fostamatinib's label (effective November 5, 2025) does 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 (TAVALISSE), Rigel Pharmaceuticals, Inc., effective November 5, 2025 (SPL set 21149cc3-049b-43e2-b141-c9499160556c), 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 | Fostamatinib | |
|---|---|---|
| Labeled for | HIV | n/a |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $2.23 per capsule 300 mg capsule | n/a |
| 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