What the FDA labels say about taking them together
Irinotecan and phenytoin
Irinotecan's FDA label of May 12, 2026 names phenytoin in its drug interactions section, and phenytoin's label names irinotecan too. The irinotecan label: “… patients concomitantly receiving the CYP3A4 enzyme-inducing anticonvulsants phenytoin and strong CYP3A4 inducers.”
Check it at the source: the irinotecan FDA label on DailyMed (effective May 12, 2026, Pharmacia & Upjohn Company LLC); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the irinotecan label say about phenytoin?
Irinotecan label, drug interactionsExposure to irinotecan or its active metabolite SN-38 is substantially reduced in adult and pediatric patients concomitantly receiving the CYP3A4 enzyme-inducing anticonvulsants phenytoin, phenobarbital, carbamazepine, or St. John's wort.
Onivyde label (Ipsen Biopharmaceuticals, Inc., March 3, 2025), drug interactionsFollowing administration of non-liposomal irinotecan (i.e., irinotecan HCl), exposure to irinotecan or its active metabolite, SN-38, is substantially reduced in adult and pediatric patients concomitantly receiving the CYP3A4 enzyme-inducing anticonvulsants phenytoin and strong CYP3A4 inducers.
Source: FDA drug label (Onivyde, NDA207793), Ipsen Biopharmaceuticals, Inc., effective March 3, 2025 (SPL set c8b58efa-1820-48a4-b70d-62918fc4abfc), via openFDA
Source: FDA drug label (Camptosar), NDA020571 (Pfizer Inc), as published by Pharmacia & Upjohn Company LLC, effective May 12, 2026 (SPL set e518dfc6-7e93-4fee-a66c-51e1ab71c056), via openFDA; the full label on DailyMed
What does the phenytoin label say about irinotecan?
Phenytoin label, drug interactionsInteracting Agent: Antineoplastic agents; Examples: Irinotecan, paclitaxel, teniposide
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
| Irinotecan | Phenytoin | |
|---|---|---|
| Labeled for | Colorectal cancer | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | n/a | $0.145 per capsule 100 mg capsule |
| Shortage now | A presentation being discontinued | 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