What the FDA labels say about taking them together
Carbamazepine and fosphenytoin
Carbamazepine's FDA label of August 20, 2026 names fosphenytoin in its drug interactions section, and fosphenytoin's label names carbamazepine too. The fosphenytoin 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 fosphenytoin FDA label on DailyMed (effective May 18, 2025, Pfizer Laboratories Div Pfizer Inc).
What does the carbamazepine label say about fosphenytoin?
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.
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.
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 (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 fosphenytoin label say about carbamazepine?
Fosphenytoin label, drug interactionsInteracting Agent: Antiepileptic drugs; Examples: Carbamazepine, vigabatrin
Fosphenytoin 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 (CEREBYX), NDA020450 (Parke Davis), as published by Pfizer Laboratories Div Pfizer Inc, effective May 18, 2025 (SPL set de5a6711-4abb-4c3d-a18b-266b094ace11), 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 | Fosphenytoin | |
|---|---|---|
| Labeled for | Bipolar disorder, Seizures and epilepsy | Seizures and epilepsy |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | $0.119 per tablet 200 mg tablet | n/a |
| 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