What the FDA labels say about taking them together
Irinotecan and phenobarbital
Irinotecan's FDA label of May 12, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name irinotecan. The irinotecan label: “Avoid the use of strong CYP3A4 inducers if possible.”
Check it at the source: the irinotecan FDA label on DailyMed (effective May 12, 2026, Pharmacia & Upjohn Company LLC); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the irinotecan label say about phenobarbital?
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 interactionsAvoid the use of strong CYP3A4 inducers (e.g., rifampin, phenytoin, carbamazepine, rifabutin, rifapentine, phenobarbital, St. John's wort) if possible.
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 phenobarbital label say about irinotecan?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name irinotecan 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
| Irinotecan | Phenobarbital | |
|---|---|---|
| Labeled for | Colorectal cancer | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | n/a | $0.213 per tablet 100 mg tablet |
| Shortage now | A presentation being discontinued | 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