What the FDA labels say about taking them together
Doravirine and phenobarbital
Doravirine's FDA label of July 8, 2026 names phenobarbital in its contraindications section; the phenobarbital 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 phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the doravirine label say about phenobarbital?
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 phenobarbital label say about doravirine?
Phenobarbital's label (effective August 27, 2026) 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 (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
| Doravirine | Phenobarbital | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $60.79 per tablet 100 mg tablet | $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