What the FDA labels say about taking them together
Phenytoin and quinidine
Phenytoin's FDA label of October 15, 2024 names quinidine in its drug interactions section, and quinidine's label names phenytoin too.
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the quinidine FDA label on DailyMed (effective February 1, 2018, Sun Pharmaceutical Industries, Inc.).
What does the phenytoin label say about quinidine?
Phenytoin label, drug interactionsInteracting Agent: Other; Examples: Corticosteroids, doxycycline, estrogens, furosemide, oral contraceptives, paroxetine, quinidine, rifampin, sertraline, theophylline, and vitamin D
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
What does the quinidine label say about phenytoin?
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
| Phenytoin | Quinidine | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Atrial fibrillation |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $4.92 per tablet 324 mg tablet |
| 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