Comparative effectiveness of eight antiepileptic drugs in adults with focal refractory epilepsy: the influence of age, gender, and the sequence in which drugs were introduced onto the market

The first objective was to determine the long-term retention rate of eight antiepileptic drugs (AEDs) commonly used as adjunctive therapy in adults with focal refractory epilepsy. Second, we assessed the effects of age and gender on retention rates. Third, we examined if the retention rate could be influenced by the sequence in which the AEDs had entered the market. Patients with focal refractory epilepsy treated with any of the eight AEDs in Tampere University Hospital were identified retrospectively (N = 507). Retention rates were evaluated with the Kaplan–Meier method. Follow-up started at the first date of treatment and each individual was followed a maximum of 36 months. We calculated the following 3-year retention rates: lacosamide 77.1% (N = 137), lamotrigine 68.3% (N = 177), levetiracetam 66.7% (N = 319), clobazam 65.6% (N = 130), topiramate 61.6% (N = 178), zonisamide 60.4% (N = 103), pregabalin 54.6% (N = 127), and gabapentin 40.2% (N = 66). Lacosamide, levetiracetam, and clobazam were the most effective AEDs in the elderly. The retention rate for pregabalin was higher in males (65%) than females (51%) whereas females had higher retention rates for both topiramate (72 vs. 58%) and zonisamide (67 vs. 57%). The retention rate was influenced by the sequence in which these AEDs entered the market. We provide important information about practical aspects of these eight AEDs, revealing that there are differences in their effectiveness as adjunctive treatment for focal refractory epilepsy. Most importantly, the retention rate appears to be influenced by the sequence in which these AEDs were introduced onto the market.