Most people who take Phenytek or other forms of phenytoin don't have too much trouble with side effects. That's one of the reasons it's used so much. The most common complaints (usually not too severe) are:

• jerking movements of the eyes
• decreased coordination
• shaking of the hands
• slowed thinking and movement
• memory problems
• slurred speech
• poor concentration

If these problems do not go away within several days, or are really bothersome, call the doctor. Most people get over these side effects without a change in the amount of Phenytek they're taking. But if the side effects continue, it is usually a sign that the level of medication in the body is too high. A change in the dose of Phenytek may help. No one should stop taking Phenytek or change the amount they take without their doctor's guidance, however.

People who have just started taking Phenytek (or who have just started taking a larger amount) should be careful during activities that might be dangerous, until they know whether they are having any side effects.

Allergic reactions
Approximately 1 in 10 people who take Phenytek have a red rash within the first few weeks of taking it. If this happens, tell the doctor or nurse right away, to be sure that it's not the beginning of a serious problem. It's rare for the rash to be serious, but don't ignore it. It's often necessary to switch to a different seizure medicine.

Long-term side effects
Some other side effects only appear after a person has been using Phenytek for a number of months or years. They are usually related to taking high doses. The most common ones affect appearance:

• overgrowth of the gums
• excessive hair on the face or body
• acne
• coarseness of facial features

Overgrowth of the gums (gingival hyperplasia) is more common in children than in adults. It can be reduced by vigorous brushing, daily flossing, and regular visits to the dentist, who may recommend additional treatments. If Phenytek is stopped, the gum problems won't get worse, and in some cases will go away within a few months.

Long-term use of Phenytek also has been found to cause weakening of the bones. Bone disease is even more likely if more than one seizure medicine is used. People taking Phenytek should exercise, take vitamin D supplements, and eat foods rich in calcium. Some non-food sources of calcium, such as Tums and Os-Cal, reduce absorption of Phenytek. They can be used but should not be taken within about 2 hours after taking the Phenytek.

Some people who take phenytoin, the medicine in Phenytek, for several years may have damage to the nerves in their legs. Faulty reflexes can be seen in a minority of this group.

Damage to the part of the brain called the cerebellum may affect others who take Phenytek for a long time, especially if they take high doses. Damage severe enough to produce significant problems is uncommon, however.