What the FDA labels say about taking them together
Dexamethasone and phenytoin
Dexamethasone's FDA label of June 6, 2025 names phenytoin in its drug interactions section; phenytoin's label does not name dexamethasone itself but warns about its class (Corticosteroids). The dexamethasone label: “Drugs which induce cytochrome P450 3A4 (CYP 3A4) enzyme activity may enhance the metabolism of corticosteroids and require that the dosage of the corticosteroid be increased.”
Check it at the source: the dexamethasone FDA label on DailyMed (effective June 6, 2025, Hikma Pharmaceuticals USA, Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the dexamethasone label say about phenytoin?
Dexamethasone label, drug interactionsDrugs which induce cytochrome P450 3A4 (CYP 3A4) enzyme activity (e.g., barbiturates, phenytoin, carbamazepine, rifampin) may enhance the metabolism of corticosteroids and require that the dosage of the corticosteroid be increased.
Hemady label (Edenbridge Pharmaceuticals LLC., January 9, 2026), drug interactionsPhenytoin In post-marketing experience, there have been reports of both increases and decreases in phenytoin levels with dexamethasone coadministration, leading to alterations in seizure control.
Source: FDA drug label (Hemady, NDA211379), Edenbridge Pharmaceuticals LLC., effective January 9, 2026 (SPL set 6b9cf32c-6d60-4853-bbfd-2304ffc2c129), via openFDA
Source: FDA drug label (Dexamethasone Intensol), Hikma Pharmaceuticals USA, Inc., effective June 6, 2025 (SPL set b15200fb-1826-472b-a907-e677a272513b), via openFDA; the full label on DailyMed
What does the phenytoin label say about dexamethasone?
Phenytoin's label does not name dexamethasone itself; it warns about its class (Corticosteroids):
Phenytoin label, drug interactionsWarfarin Increased and decreased PT/INR responses have been reported when phenytoin is coadministered with warfarin Other Corticosteroids, doxycycline, estrogens, furosemide, oral contraceptives, paroxetine, quinidine, rifampin, sertraline, theophylline, and vitamin D Drugs whose level is decreased by phenytoin Anticoagulants Apixaban, dabigatran, edoxaban, rivaroxaban Antiepileptic drugs The effect of phenytoin on phenobarbital, valproic acid and sodium valproate serum levels is unpredictable 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
| Dexamethasone | Phenytoin | |
|---|---|---|
| Labeled for | Asthma, Eczema (atopic dermatitis), Leukemia, lymphoma and myeloma, Herpes and shingles, Crohn's disease and ulcerative colitis, Multiple sclerosis, Osteoarthritis, Rheumatoid arthritis, Psoriasis, Allergies, Anemia, Pain | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.193 per tablet 4 mg tablet | $0.145 per capsule 100 mg capsule |
| Shortage now | In shortage | 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