What the FDA labels say about taking them together
Nirmatrelvir/ritonavir and phenobarbital
Nirmatrelvir/ritonavir's FDA label of February 19, 2026 names phenobarbital in its contraindications section; the phenobarbital labels PlainMeds reads (2) do not name nirmatrelvir/ritonavir. The nirmatrelvir/ritonavir label: “Co-administration contraindicated due to potential loss of virologic response and possible resistance.”
Check it at the source: the nirmatrelvir/ritonavir FDA label on DailyMed (effective February 19, 2026, Pfizer Laboratories Div Pfizer Inc); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the nirmatrelvir/ritonavir label say about phenobarbital?
Nirmatrelvir/ritonavir label, contraindicationsAnticonvulsant: carbamazepine, phenobarbital, primidone, phenytoin
Nirmatrelvir/ritonavir label, drug interactionsDrug Class: Anticonvulsants; Drugs within Class: carbamazepine, phenobarbital, primidone, phenytoin; Effect on Concentration: ↓ nirmatrelvir/ritonavir; Clinical Comments: Co-administration contraindicated due to potential loss of virologic response and possible resistance [see ].
Source: FDA drug label (Paxlovid), Pfizer Laboratories Div Pfizer Inc, effective February 19, 2026 (SPL set 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a), via openFDA; the full label on DailyMed
What does the phenobarbital label say about nirmatrelvir/ritonavir?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name nirmatrelvir/ritonavir 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
| Nirmatrelvir/ritonavir | Phenobarbital | |
|---|---|---|
| Labeled for | COVID-19 | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $49.24 per unit 300-100 mg dose pack | $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