Dilantin (phenytoin) is highly effective and may be the most commonly used seizure medicine in North America. Its effectiveness in controlling seizures has been investigated in careful scientific studies involving thousands of patients.

Many studies have compared phenytoin, the medicine in Dilantin, with other seizure medicines for the treatment of newly diagnosed epilepsy. For instance, one study of 622 adults compared phenytoin with carbamazepine (Tegretol, Carbatrol), primidone (Mysoline), and phenobarbital. All four medications were about equally effective in controlling tonic-clonic seizures. Overall, phenytoin and carbamazepine were the most successful of these four medications, largely because they caused fewer intolerable side effects than primidone or phenobarbital. The choice between phenytoin and carbamazepine will be influenced by individual needs and responses.

A similar British study of newly diagnosed epilepsy included valproate (Depakote, Depakene) instead of primidone. Again, the four medicines were about equally successful in stopping seizures. (Overall, 27% of patients had no seizures and 75% had had none for at least 1 year by the end of a 3-year follow-up.) The medications differed in the number of patients who needed to stop taking them because of intolerable side effects, however. Phenytoin had the lowest rate, only 3%.

Another study compared phenytoin with valproate in treating a group of patients with newly diagnosed generalized tonic-clonic, clonic, or tonic seizures. Of the patients treated with phenytoin, 76% had no seizures during the study period after the level of medicine in the blood reached a high enough level. The comparable figure for the patients who took valproate was 82%.

The results in everyday life are not always as good as in these studies. Sometimes patients
' take all their medicine on time, or the
' seizures cannot be controlled at a dosage that can be taken without side effects. Because of individual differences, adjustments in the amount taken are often needed to reduce seizures or side effects.

If seizures continue to occur, the doctor first may suggest a change in the dosage of Dilantin by itself (called monotherapy). If that
' work, the next step may be either to prescribe a different seizure medicine by itself or to prescribe a combination of Dilantin and another seizure medicine. (The use of more than one medicine at the same time is called combination therapy or polytherapy.) Tegretol or Carbatrol (carbamazepine) is often used in combination with Dilantin, but many other medicines are also available. No single combination is best for everyone.

Dilantin also has often been prescribed to prevent seizures in people who have suffered a serious brain injury. However, studies generally find only a short-term reduction in seizures, not long-term prevention of epilepsy.