What the FDA labels say about taking them together
Furosemide and phenytoin
Furosemide's FDA label of September 30, 2025 names phenytoin in its drug interactions section, and phenytoin's label names furosemide too. The furosemide label: “There is evidence that treatment with phenytoin leads to decreased intestinal absorption of LASIX, and consequently to lower peak serum furosemide concentrations.”
Check it at the source: the furosemide FDA label on DailyMed (effective September 30, 2025, Validus Pharmaceuticals LLC); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the furosemide label say about phenytoin?
Furosemide label, drug interactionsThere is evidence that treatment with phenytoin leads to decreased intestinal absorption of LASIX, and consequently to lower peak serum furosemide concentrations.
Furosemide label (Hikma Pharmaceuticals USA Inc., March 10, 2025), drug interactionsDrugs on Furosemide Drug/Substance Class or Name Drug Interaction Effect Recommendations Phenytoin Interferes directly with renal action of furosemide.
Source: FDA drug label (Furosemide, NDA018267), Hikma Pharmaceuticals USA Inc., effective March 10, 2025 (SPL set ddfc41a9-37d4-49c1-bbf3-969a98cd649c), via openFDA
Source: FDA drug label (Furoscix, NDA209988), scPharmaceuticals Inc., a wholly owned subsidiary of MannKind Corporation, effective July 31, 2026 (SPL set eac958dd-8d43-e44e-e053-2995a90a4d5e), via openFDA
Source: FDA drug label (Lasix), Validus Pharmaceuticals LLC, effective September 30, 2025 (SPL set 2c9b4d8f-0770-482d-a9e6-9c616a440b1a), via openFDA; the full label on DailyMed
What does the phenytoin label say about furosemide?
Phenytoin label, drug interactionsInteracting Agent: Other; Examples: Corticosteroids, doxycycline, estrogens, furosemide, oral contraceptives, paroxetine, quinidine, rifampin, sertraline, theophylline, and vitamin D
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
| Furosemide | Phenytoin | |
|---|---|---|
| Labeled for | Heart failure, High blood pressure, Edema (fluid retention) | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.490 per mL 20 mg/2 mL vial | $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