What the FDA labels say about taking them together
Istradefylline and phenytoin
Istradefylline's FDA label of May 20, 2025 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name istradefylline. The istradefylline label: “Therefore, it is recommended to avoid use of NOURIANZ with strong CYP3A4 inducers.”
Check it at the source: the istradefylline FDA label on DailyMed (effective May 20, 2025, Kyowa Kirin, Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the istradefylline label say about phenytoin?
Istradefylline label, drug interactionsTherefore, it is recommended to avoid use of NOURIANZ with strong CYP3A4 inducers (e.g., carbamazepine, rifampin, phenytoin, St. John's wort) [see Dosage and Administration (2.3) ].
Source: FDA drug label (NOURIANZ), Kyowa Kirin, Inc., effective May 20, 2025 (SPL set a7d008cb-b273-4049-a5d2-9c6902910d58), via openFDA; the full label on DailyMed
What does the phenytoin label say about istradefylline?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name istradefylline 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
| Istradefylline | Phenytoin | |
|---|---|---|
| Labeled for | Parkinson's disease | 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