Does Doxycycline Interact With Phenytoin?
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 Antiepileptic drugs a Carbamazepine, felbamate, lamotrigine, topiramate, oxcarbazepine Antilipidemic agents Atorvastatin, fluvastatin, simvastatin Antiviral agents Efavirenz, lopinavir…
Severity: Moderate
Severity basis: drug interactions section (keywords: may decrease). Combining Doxycycline (Tetracycline antibiotic) and Phenytoin (Anticonvulsant) is classified as a moderate interaction.
What to Do
Use this combination with caution. Your prescriber may monitor you more closely or adjust doses.
How This Interaction Works
Interactions like this one can happen when two medicines have overlapping effects, or when one changes how the other is absorbed, broken down, or cleared from the body. Doxycycline is a tetracycline antibiotic and Phenytoin is a anticonvulsant; together they are documented as a moderate interaction. How much this matters depends on your dose, your other medications, and your overall health.
If You Take Both Medications
If you have been prescribed both Doxycycline and Phenytoin, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.
From the FDA Label
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 Antiepileptic drugs a Carbamazepine, felbamate, lamotrigine, topiramate, oxcarbazepine Antilipidemic agents Atorvastatin, fluvastatin, simvastatin Antiviral agents Efavirenz, lopinavir…
Source: FDA structured product labeling (set_id 035a8d4e-2063-4240-83cb-d7eebcabe301).
Check these against your full medication list in our free Interaction Checker
Frequently Asked Questions
Can you take Doxycycline and Phenytoin together?
Doxycycline and Phenytoin have a documented moderate interaction. Use this combination with caution. Your prescriber may monitor you more closely or adjust doses.
How serious is the Doxycycline and Phenytoin interaction?
It is classified as a moderate interaction, based on the FDA label's drug interactions section (keywords: may decrease). A moderate interaction can be clinically meaningful and usually calls for monitoring or a dose adjustment.
What should I do if I'm taking both Doxycycline and Phenytoin?
If you have been prescribed both Doxycycline and Phenytoin, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.
This information is educational — not medical advice.
This page is provided for general educational purposes and summarizes publicly available data from sources such as the U.S. Food & Drug Administration. It is not a substitute for the judgment of a licensed clinician and should not be used to start, stop, or change any medication. It may be incomplete or out of date, and individual circumstances vary. Always talk with your prescriber or pharmacist about your specific medications and health conditions. If you think you may have a medical emergency, call 911.
Other Doxycycline Interactions
Other Phenytoin Interactions
- Phenytoin + Apixaban(major)
- Phenytoin + Itraconazole(major)
- Phenytoin + Methotrexate(major)
- Phenytoin + Rifampin(major)
- Phenytoin + Rivaroxaban(major)
- Phenytoin + Ticagrelor(major)
- Phenytoin + Amiodarone(moderate)
- Phenytoin + Atorvastatin(moderate)
- Phenytoin + Carbamazepine(moderate)
- Phenytoin + Carbidopa Levodopa(moderate)
- Phenytoin + Cholecalciferol(moderate)
- Phenytoin + Clarithromycin(moderate)
- Phenytoin + Cyclosporine(moderate)
- Phenytoin + Diazepam(moderate)
- Phenytoin + Digoxin(moderate)
- Phenytoin + Fluconazole(moderate)
- Phenytoin + Fluoxetine(moderate)
- Phenytoin + Folic Acid(moderate)
- Phenytoin + Furosemide(moderate)
- Phenytoin + Glimepiride(moderate)
- Phenytoin + Hydrocodone Acetaminophen(moderate)
- Phenytoin + Ketoconazole(moderate)
- Phenytoin + Lamotrigine(moderate)
- Phenytoin + Lithium(moderate)
- Phenytoin + Methylphenidate(moderate)
- Phenytoin + Methylprednisolone(moderate)
- Phenytoin + Mirtazapine(moderate)
- Phenytoin + Nifedipine(moderate)
- Phenytoin + Omeprazole(moderate)
- Phenytoin + Oxycodone(moderate)
- Phenytoin + Paroxetine(moderate)
- Phenytoin + Quetiapine(moderate)
- Phenytoin + Sertraline(moderate)
- Phenytoin + Simvastatin(moderate)
- Phenytoin + Tacrolimus(moderate)
- Phenytoin + Topiramate(moderate)
- Phenytoin + Tramadol(moderate)
- Phenytoin + Trazodone(moderate)
- Phenytoin + Sulfamethoxazole Trimethoprim(moderate)
- Phenytoin + Verapamil(moderate)
- Phenytoin + Warfarin(moderate)
- Phenytoin + Alprazolam(minor)
- Phenytoin + Atomoxetine(minor)
- Phenytoin + Azithromycin(minor)
- Phenytoin + Buprenorphine Naloxone(minor)
- Phenytoin + Bupropion(minor)
- Phenytoin + Canagliflozin(minor)
- Phenytoin + Clonazepam(minor)
- Phenytoin + Codeine(minor)
- Phenytoin + Dexamethasone(minor)
- Phenytoin + Gabapentin(minor)
- Phenytoin + Glipizide(minor)
- Phenytoin + Levothyroxine(minor)
- Phenytoin + Liothyronine(minor)
- Phenytoin + Metformin(minor)
- Phenytoin + Metronidazole(minor)
- Phenytoin + Modafinil(minor)
- Phenytoin + Ondansetron(minor)
- Phenytoin + Pregabalin(minor)
- Phenytoin + Sucralfate(minor)
- Phenytoin + Tadalafil(minor)
- Phenytoin + Valproic Acid(minor)