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Phenytek®
 

Efficacy of Phenytek

Phenytoin may be the most commonly used antiepileptic medication in North America. Its effectiveness in controlling seizures has been extensively studied in careful scientific trials in great numbers of patients.

Many studies have compared phenytoin with other antiepileptic medications for the treatment of newly diagnosed epilepsy. For instance, one study of 622 adults compared phenytoin with carbamazepine, primidone, 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 instead of primidone. Again, the efficacy of the four medications in stopping seizures was about equal. (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 The medications differed in the number of patients who needed to have the medication withdrawn because of intolerable side effects, however. The lowest rate of withdrawal (3%) was reported for patients taking phenytoin.

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 a therapeutic blood level was reached. The comparable figure for the patients who took valproate was 82%.

Phenytoin is best used for partial-onset seizures. It generally is not effective against generalized-onset absence seizures or infantile spasms. It has limited value in clonic, myoclonic, and atonic seizures and in the Lennox-Gastaut syndrome. It may control the tonic-clonic component of the syndrome.

If phenytoin alone does not fully control the patient's seizures, a combination of phenytoin and another medication may be more effective. Many doctors start with a combination of phenytoin and carbamazepine, but a number of newly developed medications are also available. Sometimes a series of combinations must be tried before finding what is best for the individual patient.

Phenytoin has often been prescribed to prevent seizures in patients who have suffered a serious brain injury. However, a 2-year study to determine the efficacy of phenytoin in preventing seizures after head trauma demonstrated only short-term benefit. Patients who were given phenytoin instead of placebo had fewer seizures (but not lower mortality) during the first week but not over a longer period. These researchers also found that severely injured patients experienced negative cognitive effects while taking the phenytoin.