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Drug Interactions With Phenytoin
Certain medications -- including paroxetine, cimetidine, and carbamazepine -- may potentially cause drug interactions with phenytoin. These interactions may potentially affect the level of phenytoin in your blood, raise your risk of side effects, or decrease the effectiveness of some medicines. If phenytoin drug interactions occur, your healthcare provider may need to measure the level of phenytoin in your blood and adjust your dosage as necessary.
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Phenytoin (Dilantin®) can potentially interact with many other medications. Some of these medicines that may lead to phenytoin interactions include:
- Alcohol
- Amiodarone (Cordarone®)
- Carbamazepine (Epitol®, Equetro™, Tegretol®, Tegretol XR®)
- Calcium-containing products (including calcium supplements and certain antacids)
- Chlordiazepoxide (Librium®, Librax®, Limbitrol®)
- Cimetidine (Tagamet®)
- Corticosteroids, such as dexamethasone (Decadron®), methylprednisolone (Depo-Medrol®, Medrol®), prednisone, and many others
- Diazepam (Valium®)
- Digoxin (Digitek®, Lanoxin®)
- Disulfiram (Antabuse®)
- Doxycycline
- Estrogen medications, including oral contraceptives and hormone replacement therapy (HRT)
- Ethosuximide (Zarontin®)
- Fluoxetine (Prozac®, Sarafem®)
- Furosemide (Lasix®)
- H2 blockers, including:
- Cimetidine (Tagamet®)
- Famotidine (Pepcid®)
- Nizatidine (Axid®)
- Ranitidine (Zantac®)
- Isoniazid
- Methylphenidate (Concerta®, Daytrana®, Metadate CD®, Metadate ER®, Methylin®, Ritalin®, Ritalin LA®, Ritalin SR®)
- Paroxetine (Paxil®, Paxil CR®)
- Phenobarbital
- Phenothiazine medications, including:
- Quinidine
- Reserpine
- Rifampin (Rifadin®)
- Salicylates, such as aspirin (Ecotrin®, Bayer®, Anacin®), choline magnesium trisalicylate (Trilisate®), diflunisal (Dolobid®), and salsalate (Salflex®, Disalcid®, Amigesic®)
- Sucralfate (Carafate®)
- Sulfonamides ("sulfa drugs"), including sulfadiazine, sulfadoxine (Fansidar®), sulfamethoxazole (Bactrim®, Septra®), and sulfisoxazole (Gantrisin®)
- Ticlopidine (Ticlid®)
- Theophylline
- Tolbutamide (Orinase®)
- Trazodone (Desyrel®) or trazodone ER (Oleptro™)
- Valproic acid (Depakene®) or divalproex sodium (Depakote®, Depakote ER®)
- Warfarin (Coumadin®, Jantoven®).
Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD