Doxycycline and Phenytoin interaction
Doxycycline and Phenytoin: both prescribing labels describe an interaction that usually calls for monitoring, a dose change, or spacing the doses.
Usually manageable with monitoring or a dose change. Tell your pharmacist you take both.
What the FDA labels say
From the Doxycycline (Doxycycline Hyclate) label · effective 2026-06-30
Barbiturates, carbamazepine and phenytoin decrease the half-life of doxycycline.
Barbiturates and Anti-Epileptics Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.
From the Phenytoin label · effective 2024-12-24
Warfarin 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…
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.