How reliable is early treatment response in predicting long-term seizure outcome?

Assessing if an early therapeutic response to an antiepileptic drug (AED) is of prognostic value for long-term outcome is of considerable clinical interest. To that end, we evaluated the likelihood that a patient who becomes seizure-free after 6 months of treatment with a single AED would lose that response at 12 months, or vice versa. In a post hoc analysis, data from five comparative, double-blind, single-drug studies designed to evaluate the efficacy of treatment of patients with partial seizures with oxcarbazepine versus carbamazepine, phenobarbital, phenytoin, and valproate for approximately 1 year were pooled to investigate same-patient seizure outcome at 6 and 12 months. These studies had similar dosing regimens and included a wide range of patients with newly diagnosed and chronic epilepsy. The main finding in the population included in the analysis is that those patients who are seizure-free at 6 months have a 90% chance of being seizure-free at 12 months, whereas those not seizure-free at 6 months have only a 45% chance of being seizure-free at 12 months (χ2 = 118.716, P < 0.000001, odds ratio = 11.23 with 95% confidence limits 6.8–18.7). In a worst-case assessment, those not seizure-free at 6 months have only an 18% chance of being seizure-free at 12 months (χ2 = 408.105, P < 0.000001, odds ratio = 41.23 with 95% confidence limits 26.4–65.85). Failure to maintain the response in 10% of patients, including 4% with two or more seizures, was noted with all AEDs studied here and in patients with newly diagnosed as well as chronic epilepsy. Among patients with seizures in Months 1–6, those with newly diagnosed epilepsy became seizure-free more often over time than those with chronic epilepsy. The main conclusion is that response at 6 months is an excellent predictor of response at 12 months.