What the FDA labels say about taking them together
Phenytoin and trimethoprim
Trimethoprim's FDA label of January 26, 2024 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name trimethoprim.
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the trimethoprim FDA label on DailyMed (effective January 26, 2024, Dr. Reddy's Labratories Inc.).
What does the phenytoin label say about trimethoprim?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name trimethoprim in these sections. A label lists what its studies and reports found; it is not a complete list.
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 trimethoprim label say about phenytoin?
Trimethoprim label, drug interactionsDrug Interactions Trimethoprim may inhibit the hepatic metabolism of phenytoin.
Source: FDA drug label (Trimethoprim), NDA018679 (Dr Reddys Labs Sa), as published by Dr. Reddy's Labratories Inc., effective January 26, 2024 (SPL set 73ccebc1-7412-2424-d62c-a5180ec52d81), 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 | Trimethoprim | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Bacterial infections, Urinary tract infections |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $1.31 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