Phenytoin is the generic name of a widely used antiepileptic drug (AED). In the United States, phenytoin is known by the brand names Dilantin and Phenytek (an extended-release form). In the UK, the brand name is Epanutin.

Sometimes the savings from using generic medications instead of brand-name products are large, but with other products the price differences are rather small. Investigate before deciding whether the savings are worth any possible problems. What's important is that both the doctor and the patient should know what the pharmacy is dispensing and have control over what type of medication is used.

Patients who switch from brand-name Dilantin to generic phenytoin possibly risk having more seizures or side effects during the changeover, because of differences in absorption or metabolism. Switching from one company's generic phenytoin to another company's may have similar risks. So can switching from generic phenytoin to Dilantin.

All these risks are not fully known. For some patients the effects of changing from one type to another are very small. Some use generic phenytoin successfully by always using the same company's product. Then the dosage can be adjusted to achieve the best results.

Forms of phenytoin
Various companies make and sell phenytoin or phenytoin sodium. In the United States, it is generally available in three forms:

• 100-mg capsules
• 125 mg/5mL suspension
• 50 mg/mL injectable solution

How to take and store phenytoin
Capsules should be swallowed whole, not chewed or broken open. They should be stored at a temperature below 86°F (30°C) and protected from light and moisture. Capsules that are discolored should not be used.

The suspension should be stored at room temperature, between 68º and 77ºF (20°-25°C), and should be protected from light and from freezing. Remind patients to shake the bottle well just before measuring and to use an accurate measuring device.

All forms of phenytoin can be taken either with food or without food, but patients should be advised to be consistent. Taking it with food lengthens the time for absorption but produces higher concentrations.

Missed doses
Advise patients to take a forgotten dose immediately. If it is almost time for the next dose, they should either skip the forgotten dose (rather than taking a double dose) or make it up with the next 2 or 3 doses.

Patients who often forget doses may benefit from using a special pillbox or watch with an alarm. Switching to a once-a-day extended-release form (in the U.S., Phenytek) may also help with compliance.