GENERIC AVAILABLE: Yes
PREPARATIONS: Capsules (extended or immediate release): 30, 100, 200, and 300 mg; Chewable Tablet: 50 mg; Suspension: 125 mg/5 mL; Injection: 50 mg/mL.
STORAGE: Capsules, tablets, and suspension should be kept at room temperature, 68 F - 77 F (20 C - 25 C).
DOSING: The dosing of phenytoin is patient specific. It may be given once, twice, 3, or 4 times daily. Doses are often adjusted to find the optimal dose based on measurement of blood levels. Taking phenytoin with food may reduce some of the side effects. Elderly patients, debilitated persons, and patients with certain kidney or liver diseases may need lower doses. The suspension should not be given at the same time as tube feedings since tube feedings bind to phenytoin and reduce its absorption. The recommended adult dose is 100 mg two to four times daily. Some patients may require 200 mg three times daily. Patients stabilized on 100 mg three times daily may receive 300 mg once daily of the extended release capsules.
DRUG INTERACTIONS: There are many potential drug interactions with phenytoin. Phenytoin can increase the metabolism (elimination) of many drugs, reducing their concentrations in the body. Drugs that may be affected include:
- digoxin (Lanoxin),
- carbamazepine (Tegretol, Tegretol XR, Equetro, Carbatrol),
- clonazepam (Klonopin),
- corticosteroids (for example, prednisone),
- oral contraceptives,
- paroxetine (Paxil, Paxil CR, Pexeva),
- tacrolimus (Prograf),
- valproic acid (Depakote, Depakote ER, Depakene, Depacon, Stavzor), and
- warfarin (Coumadin).
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