What the FDA labels say about taking them together
Doravirine and phenytoin
Doravirine's FDA label of July 8, 2026 names phenytoin in its contraindications section; the phenytoin labels PlainMeds reads (2) do not name doravirine. The doravirine label: “Co-administration is contraindicated with these anticonvulsants. At least a 4-week cessation period is recommended prior to initiation of PIFELTRO.”
Check it at the source: the doravirine FDA label on DailyMed (effective July 8, 2026, Merck Sharp & Dohme LLC); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the doravirine label say about phenytoin?
Doravirine label, contraindicationsThese drugs include, but are not limited to, the following: the anticonvulsants carbamazepine, oxcarbazepine, phenobarbital, phenytoin the androgen receptor inhibitor enzalutamide the antimycobacterials rifampin, rifapentine the cytotoxic agent mitotane St. John's wort ( Hypericum perforatum) PIFELTRO is contraindicated when co-administered with drugs that are strong cytochrome P450 (CYP)3A enzyme inducers as significant decreases in doravirine plasma concentrations may occur, which may decrease the effectiveness of PIFELTRO.
Doravirine label, drug interactionsConcomitant Drug Class/Drug Name: carbamazepine oxcarbazepine phenobarbital phenytoin; Effect on Concentration: ↓ doravirine; Clinical Comment: Co-administration is contraindicated with these anticonvulsants. At least a 4-week cessation period is recommended prior to initiation of PIFELTRO.
Source: FDA drug label (PIFELTRO), Merck Sharp & Dohme LLC, effective July 8, 2026 (SPL set 76ce1f00-28c0-4314-bd2c-d473fe3d0970), via openFDA; the full label on DailyMed
What does the phenytoin label say about doravirine?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name doravirine 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
| Doravirine | Phenytoin | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $60.79 per tablet 100 mg tablet | $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