What the FDA labels say about taking them together
Phenobarbital and quinidine
Quinidine's FDA label of February 1, 2018 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name quinidine.
Check it at the source: the phenobarbital FDA label on DailyMed (effective August 27, 2026); the quinidine FDA label on DailyMed (effective February 1, 2018, Sun Pharmaceutical Industries, Inc.).
What does the phenobarbital label say about quinidine?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name quinidine 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
What does the quinidine label say about phenobarbital?
Quinidine label, drug interactionsHepatic elimination of quinidine may be accelerated by coadministration of drugs ( phenobarbital, phenytoin, rifampin ) that induce production of cytochrome P450 IIIA4 .
Source: FDA drug label (Quinidine Gluconate), Sun Pharmaceutical Industries, Inc., effective February 1, 2018 (SPL set 5023f053-fcc4-4c2c-aa59-9ec198ad185e), 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
| Phenobarbital | Quinidine | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Atrial fibrillation |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.213 per tablet 100 mg tablet | $4.92 per tablet 324 mg tablet |
| Shortage now | A presentation being discontinued | 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