In an attempt to answer this question, Dr. Mintzer and colleagues examined patients with focal epilepsy who were switched from an enzyme inducer to levetiracetam, lamotrigine, or topiramate. Eligible patients had taken their first drug for at least six months, and the researchers categorized them as being seizure-free or not. Each patient was matched with two control participants who had the same seizure status as the intervention patient but who remained on their original antiepileptic drugs (AEDs). The investigators performed a consecutive, retrospective chart review.
The rate of relapse at six months was 21.7% among patients who were seizure-free at baseline and who subsequently switched AEDs, compared with 4.3% among controls who were seizure-free at baseline and who continued taking their original AEDs. Therefore, switching medication for a seizure-free patient entails an approximately 17% excess risk of recurrent seizure, said Dr. Mintzer.
Among patients who were not seizure-free at baseline and who switched to a new AED, 30% became seizure-free at six months. Among patients who were not seizure-free at baseline and who continued their original AED, 20% became seizure-free at six months. The result indicates that “not everything that happens may be due to drug changes,” said Dr. Mintzer.
The investigators performed statistical comparison adjustment to compensate for differences in the number of drugs failed between the case and control participants. After adjustment, patients who were seizure-free and who switched AEDs had 6.5 times greater odds of relapsing than patients who continued to take the same drug. The result fell short of statistical significance but was “a pretty strong trend,” said Dr. Mintzer. “In the nonseizure-free patients, we were able to demonstrate, as we’d shown in other studies, that the more AEDs you fail, the worse your outcome is likely to be,” he concluded.
—Erik Greb