Fosphenytoin

267 interactions 11 explained in plain English
Also sold as: Cerebyx
Dr. Brian Staiger, PharmD, BCPS
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: Lurasidone Nifedipine Lenacapavir Oral Fostemsavir Doravirine Lenacapavir Injection
6 Contraindicated 229 Major 31 Moderate 1 Minor
All (267) Contraindicated (6) Major (229) Moderate (31) Minor (1)

Moderate

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

Check another drug

Still have questions about this combination?

Every question gets a real answer from a licensed pharmacist — free, and usually within a day.

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