What the FDA labels say about taking them together
Gefitinib and phenytoin
Gefitinib's FDA label of February 28, 2023 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name gefitinib. The gefitinib label: “Increase IRESSA to 500 mg daily in patients receiving a strong CYP3A4 inducer and resume IRESSA at 250 mg 7 days after discontinuation of the strong inducer.”
Check it at the source: the gefitinib FDA label on DailyMed (effective February 28, 2023, AstraZeneca Pharmaceuticals LP); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the gefitinib label say about phenytoin?
Gefitinib label, drug interactionsIncrease IRESSA to 500 mg daily in patients receiving a strong CYP3A4 inducer (e.g., rifampicin, phenytoin, or tricyclic antidepressant) and resume IRESSA at 250 mg 7 days after discontinuation of the strong inducer [see Dosage and Administration (2.4), Clinical Pharmacology (12.3) ].
Source: FDA drug label (IRESSA), AstraZeneca Pharmaceuticals LP, effective February 28, 2023 (SPL set 827d60e8-7e07-41b7-c28b-49ef1c4a5a41), via openFDA; the full label on DailyMed
What does the phenytoin label say about gefitinib?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name gefitinib 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
| Gefitinib | Phenytoin | |
|---|---|---|
| Labeled for | Lung cancer | 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