What the FDA labels say about taking them together
Aminophylline and phenytoin
Aminophylline's FDA label of May 22, 2026 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name aminophylline. The aminophylline label: “Phenytoin Phenytoin increases theophylline clearance by increasing microsomal enzyme activity.”
Check it at the source: the aminophylline FDA label on DailyMed (effective May 22, 2026, Hospira, Inc.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the aminophylline label say about phenytoin?
Aminophylline label, drug interactionsPhenytoin Phenytoin increases theophylline clearance by increasing microsomal enzyme activity.
Source: FDA drug label (Aminophylline), Hospira, Inc., effective May 22, 2026 (SPL set 9a663ef3-881f-48bd-2689-3713b24545c2), via openFDA; the full label on DailyMed
What does the phenytoin label say about aminophylline?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name aminophylline 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
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
| Aminophylline | Phenytoin | |
|---|---|---|
| Labeled for | Asthma | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.145 per capsule 100 mg capsule |
| 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