What the FDA labels say about taking them together
Erlotinib and phenobarbital
Erlotinib's FDA label of June 10, 2024 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name erlotinib. The erlotinib label: “Increase the erlotinib dosage if co-administration with CYP3A4 inducers is unavoidable.”
Check it at the source: the erlotinib FDA label on DailyMed (effective June 10, 2024, Alembic Pharmaceuticals Limited); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the erlotinib label say about phenobarbital?
Erlotinib label, drug interactionsIncrease the erlotinib dosage if co-administration with CYP3A4 inducers (e.g., carbamazepine, phenytoin, rifampin, rifabutin, rifapentine, phenobarbital and St. John's wort) is unavoidable [see Dosage and Administration (2.4)].
Source: FDA drug label (ERLOTINIB HYDROCHLORIDE), Alembic Pharmaceuticals Limited, effective June 10, 2024 (SPL set ab6f3cb3-34a8-4492-a5d7-fb6b055a2d6b), via openFDA; the full label on DailyMed
What does the phenobarbital label say about erlotinib?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name erlotinib 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
| Erlotinib | Phenobarbital | |
|---|---|---|
| Labeled for | Lung cancer | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.213 per tablet 100 mg tablet |
| Shortage now | No current entry | 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