What the FDA labels say about taking them together
Carbamazepine and phenytoin
Carbamazepine's FDA label of August 20, 2026 names phenytoin in its drug interactions section, and phenytoin's label names carbamazepine too. The phenytoin label: “… HLA-B*1502, an inherited allelic variant of the HLA B gene, in patients using carbamazepine.”
Check it at the source: the carbamazepine FDA label on DailyMed (effective August 20, 2026, Novartis Pharmaceuticals Corporation); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the carbamazepine label say about phenytoin?
Carbamazepine label, drug interactionsDrugs that have been shown, or that would be expected, to decrease plasma carbamazepine levels include cisplatin, doxorubicin HCl, felbamate, fosphenytoin, rifampin, phenobarbital, phenytoin, primidone, methsuximide, theophylline, aminophylline.
Carbamazepine label, warningsLimited evidence suggests that HLA-B*1502 may be a risk factor for the development of SJS/TEN in patients of Chinese ancestry taking other antiepileptic drugs associated with SJS/TEN, including phenytoin.
Carbatrol label (Takeda Pharmaceuticals America, Inc., August 17, 2026), drug interactionsAminophylline, cisplatin, doxorubicin HCL, felbamate, fosphenytoin, methsuximide, phenobarbital, phenytoin (1), primidone, rifampin and theophylline. (1) Phenytoin plasma levels have also been reported to increase and decrease in the presence of carbamazepine, see below.
Equetro label (Validus Pharmaceuticals LLC, August 19, 2025), drug interactionsDRUG INTERACTIONS Cytochrome (CYP) 3A4 inhibitors, epoxide hydrolase inhibitors, CYP3A4 inducers, drugs metabolized by CYP1A2 or CYP3A4 (oral contraceptives, delavirdine, nefazodone), phenytoin, CNS depressants, lithium, chloroquine, mefloquine ( 7.1 , 7.2 , 7.3 ) Equetro may decrease the effectiveness of hormonal contraceptives.
Source: FDA drug label (Carbatrol, NDA020712), Takeda Pharmaceuticals America, Inc., effective August 17, 2026 (SPL set bc03e499-5bac-4293-bff4-6864153a624d), via openFDA
Source: FDA drug label (Equetro, NDA021710), Validus Pharmaceuticals LLC, effective August 19, 2025 (SPL set be478f3c-40f6-47cc-8ab9-f420a9372b1c), via openFDA
Source: FDA drug label (Tegretol), Novartis Pharmaceuticals Corporation, effective August 20, 2026 (SPL set 8d409411-aa9f-4f3a-a52c-fbcb0c3ec053), via openFDA; the full label on DailyMed
What does the phenytoin label say about carbamazepine?
Phenytoin label, drug interactionsInteracting Agent: Antiepileptic drugs; Examples: Carbamazepine, vigabatrin
Phenytoin label, warnings and precautionsStudies in patients of Chinese ancestry have found a strong association between the risk of developing SJS/TEN and the presence of HLA-B*1502, an inherited allelic variant of the HLA B gene, in patients using carbamazepine.
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
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
| Carbamazepine | Phenytoin | |
|---|---|---|
| Labeled for | Bipolar disorder, Seizures and epilepsy | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.119 per tablet 200 mg tablet | $0.145 per capsule 100 mg capsule |
| 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