Phenytoin

237 interactions 11 explained in plain English

Also sold as: Dilantin Phenytek

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Updated Jul 4, 2026 · Editorial policy · Data sources

Sources: FDA prescribing information (Structured Product Labeling), the published literature cited in each entry, DDInter 2.0 (a major open-access drug-interaction database), and legacy DrugBank interaction data distributed by the NIH's RxNav service (decommissioned in 2024) — analyzed and reviewed by our pharmacist team. How we build this library →

Most serious with: Cabotegravir Lenacapavir Oral Doravirine Lenacapavir Injection Lurasidone Fostemsavir

7 Contraindicated 191 Major 38 Moderate 1 Minor

All (237) Contraindicated (7) Major (191) Moderate (38) Minor (1)

Moderate

Phenytoin Acetaminophen And Codeine Capital® & Codeine Explained Decreased acetaminophen effectiveness and an increased risk of hepatotoxicity Details Phenytoin Acetaminophen Acephen Decreased acetaminophen effectiveness and an increased risk of hepatotoxicity Details Phenytoin Acetaminophen Injection Acephen Decreased acetaminophen effectiveness and an increased risk of hepatotoxicity Details Phenytoin Acetaminophen Rectal Acephen Decreased acetaminophen effectiveness and an increased risk of hepatotoxicity Details Phenytoin Acetazolamide Diamox® Sequels® An increased risk of osteomalacia Details Phenytoin Acitretin Soriatane® Increased free phenytoin concentrations and risk of toxic effects Details Phenytoin Acyclovir Avaclyr Decreased phenytoin plasma concentrations and potential increased seizure activity Details Phenytoin Acyclovir Injection Avaclyr Decreased phenytoin plasma concentrations and potential increased seizure activity Details Phenytoin Acyclovir Ophthalmic Avaclyr Decreased phenytoin plasma concentrations and potential increased seizure activity Details Phenytoin Acyclovir Topical Zovirax Decreased phenytoin plasma concentrations and potential increased seizure activity Details Phenytoin Azithromycin AzaSite Increased phenytoin exposure Details Phenytoin Anagrelide Agrylin Decreased anagrelide exposure Details Phenytoin Bexarotene Targretin Decreased plasma levels of bexarotene Details Phenytoin Bexarotene Topical Targretin Decreased plasma levels of bexarotene Details Phenytoin Bromfenac Ophthalmic Bromday® Decreased bromfenac efficacy Details Phenytoin Busulfan Injection Busulfex Decreased plasma concentrations of busulfan Details Phenytoin Carmustine BiCNU Decreased serum phenytoin concentrations Details Phenytoin Carmustine Implant Gliadel Decreased serum phenytoin concentrations Details Phenytoin Caspofungin Injection Cancidas Reduced caspofungin plasma levels Details Phenytoin Clopidogrel Plavix Increased clopidogrel active metabolite exposure and an increased platelet inhibition Details Phenytoin Colesevelam Welchol Decreased phenytoin exposure Details Phenytoin Guanfacine Intuniv Decreased guanfacine exposure Details Phenytoin Leucovorin Vykoura Reduced efficacy phenytoin or fosphenytoin (prodrug of phenytoin) and an increased risk or frequency of seizures Details Phenytoin Leucovorin Injection Vykoura Reduced efficacy phenytoin or fosphenytoin (prodrug of phenytoin) and an increased risk or frequency of seizures Details Phenytoin Levodopa Oral Inhalation Inbrija Decreased levodopa effectiveness Details Phenytoin Levofloxacin Levaquin Decrease in phenytoin levels Details Phenytoin Levofloxacin Injection Levaquin Decrease in phenytoin levels Details Phenytoin Levothyroxine Ermeza Reduced efficacy of levothyroxine Details Phenytoin Linezolid Injection Zyvox Decreased linezolid serum concentrations Details Phenytoin Lithium Carbonate Lithobid Additive risk of toxic side effects Details Phenytoin Metformin Fortamet® An increased risk of hyperglycemia and potential loss of glycemic control Details Phenytoin Midazolam Nasal Spray Nayzilam Decreased efficacy of midazolam Details Phenytoin Midazolam Injection Nayzilam Decreased efficacy of midazolam Details Phenytoin Naldemedine Symproic Reduced naldemedine exposure and decreased efficacy Details Phenytoin Naproxen Aleve Increased free hydantoin plasma concentrations Details Phenytoin Nateglinide Starlix® Reduced hypoglycemic action of nateglinide Details Phenytoin Nilutamide Nilandron An increased risk of phenytoin toxicity (ataxia, hyperreflexia, nystagmus, or tremor) Details Phenytoin Ospemifene Osphena Decreased ospemifene exposure and efficacy Details

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Educational information only, not medical advice. Always confirm interactions with your pharmacist or prescriber before making any change to your medications.