What the FDA labels say about taking them together
Doxycycline and phenytoin
Doxycycline's FDA label (Doxycycline Hyclate) of June 30, 2026 names phenytoin in its drug interactions section, and phenytoin's label names doxycycline too. The doxycycline label: “Barbiturates and Anti-epileptics Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.”
Check it at the source: the doxycycline FDA label on DailyMed (effective July 25, 2025, Chartwell RX, LLC.); the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.).
What does the doxycycline label say about phenytoin?
Doxycycline Hyclate label (Chartwell RX, LLC, June 30, 2026), drug interactionsDRUG INTERACTIONS Patients who are on anticoagulant therapy may require downward adjustment of their anticoagulant dosage. ( 7.1 ) Avoid co-administration of tetracyclines with penicillin. ( 7.2 ) Absorption of tetracyclines, including doxycycline hyclate is impaired by antacids containing aluminum, calcium, or magnesium, bismuth subsalicylate and iron-containing preparations. ( 7.3 ) Concurrent use of tetracyclines, including doxycycline hyclate may render oral contraceptives less effective. ( 7.4 ) Barbiturates, carbamazepine and phenytoin decrease the half-life of doxycycline.
Oracea label (Galderma Laboratories, L.P., April 16, 2025), drug interactionsBarbiturates and Anti-epileptics Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.
Source: FDA drug label (Doxycycline Hyclate, NDA205931), Chartwell RX, LLC, effective June 30, 2026 (SPL set fad03768-f1d2-459f-965e-0ec29f189f1f), via openFDA
Source: FDA drug label (Oracea, NDA050805), Galderma Laboratories, L.P., effective April 16, 2025 (SPL set aa15c93a-ff4c-447a-8a21-96da506d8997), via openFDA
Source: FDA drug label (Acticlate Cap, NDA208253), Aqua Pharmaceuticals, effective November 28, 2017 (SPL set 5e96d473-63dd-4446-88cf-eef2cd3339f0), via openFDA
Source: FDA drug label (Doxycycline Monohydrate), Chartwell RX, LLC., effective July 25, 2025 (SPL set 02aa8731-d40f-43d8-8b63-a79a0503f8db), via openFDA; the full label on DailyMed
What does the phenytoin label say about doxycycline?
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
| Doxycycline | Phenytoin | |
|---|---|---|
| Labeled for | Urinary tract infections, Bacterial infections, Acne | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.118 per tablet 100 mg tablet | $0.145 per capsule 100 mg capsule |
| Shortage now | A presentation being discontinued | 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