What the FDA labels say about taking them together
Phenytoin and prednisolone
Prednisolone's FDA label of June 25, 2026 names phenytoin in its drug interactions section; phenytoin's label does not name prednisolone itself but warns about its class (Corticosteroids). The prednisolone label: “Drug Interactions Drugs such as barbiturates, phenytoin, ephedrine, and rifampin, which induce hepatic microsomal drug metabolizing enzyme activity may enhance metabolism of prednisolone and require that the dosage of …”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the prednisolone FDA label on DailyMed (effective June 25, 2026, PAI Holdings, LLC dba PAI Pharma).
What does the phenytoin label say about prednisolone?
Phenytoin's label does not name prednisolone 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
What does the prednisolone label say about phenytoin?
Prednisolone label, drug interactionsDrug Interactions Drugs such as barbiturates, phenytoin, ephedrine, and rifampin, which induce hepatic microsomal drug metabolizing enzyme activity may enhance metabolism of prednisolone and require that the dosage of Prednisolone Sodium Phosphate Oral Solution be increased.
Orapred Odt label (Advanz Pharma (US) Corp., June 3, 2025), drug interactionsCYP 3A4 inducers (e.g. barbiturates, phenytoin, carbamazepine, and rifampin): Drugs such as barbiturates, phenytoin, ephedrine, and rifampin, which induce hepatic microsomal drug metabolizing enzyme activity may enhance metabolism of prednisolone and require that the dosage of Orapred be increased.
Source: FDA drug label (Orapred Odt, NDA021959), Advanz Pharma (US) Corp., effective June 3, 2025 (SPL set 1e379543-c4cf-4e72-953b-db15b7f0c2a1), via openFDA
Source: FDA drug label (PrednisoLONE Sodium Phosphate), PAI Holdings, LLC dba PAI Pharma, effective June 25, 2026 (SPL set d1f937e7-fed5-4079-bd52-5d930b34ae9f), 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 | Prednisolone | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Anemia, Leukemia, lymphoma and myeloma, Multiple sclerosis, Osteoarthritis, Asthma, Allergies, Herpes and shingles, Crohn's disease and ulcerative colitis, Eczema (atopic dermatitis), Organ transplant rejection |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $4.72 per mL 1% eye drop |
| 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