What the FDA labels say about taking them together
Phenytoin and topiramate
Phenytoin's FDA label of October 15, 2024 names topiramate in its drug interactions section, and topiramate's label names phenytoin too. The topiramate label: “Concomitant administration of phenytoin or carbamazepine with topiramate resulted in a clinically significant decrease in plasma concentrations of topiramate when compared to topiramate given alone.”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the topiramate FDA label on DailyMed (effective June 1, 2026, Sun Pharmaceutical Industries, Inc.).
What does the phenytoin label say about topiramate?
Phenytoin label, drug interactionsInteracting Agent: Antiepileptic drugs; Examples: Ethosuximide, felbamate, oxcarbazepine, methsuximide, topiramate
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 topiramate label say about phenytoin?
Topiramate label, drug interactionsConcomitant administration of phenytoin or carbamazepine with topiramate resulted in a clinically significant decrease in plasma concentrations of topiramate when compared to topiramate given alone.
Source: FDA drug label (Topiramate), Sun Pharmaceutical Industries, Inc., effective June 1, 2026 (SPL set 3c909a53-ae66-4b28-a741-b60bb25a69cf), 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 | Topiramate | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Seizures and epilepsy, Migraine |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $0.0567 per tablet 100 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