Efficacy, tolerability, and blood concentration of zonisamide in daily clinical practice

We aimed to evaluate the efficacy, tolerability, and blood concentration of zonisamide (ZNS) used in daily clinical practice. This was a retrospective study performed at a single epilepsy center and included 149 patients with epilepsy. The efficacy and retention of ZNS for 52 weeks, percentage of patients who were seizure free for 26 weeks, and the 5-year retention rate were analyzed. The tolerability was assessed based on treatment-emergent adverse effects (AEs) and the adverse effect profile (AEP). More than 70% (105/149) of patients were on ZNS polytherapy. The mean dose of ZNS was 300 ± 170.6 mg/day, and the antiepileptic drug (AED) load was 2.0 ± 1.1 (median 1.8, range 0.2-5.3). The retention rate for 52 weeks and the percentage of patients who were seizure-free for 26 weeks were 73% and 42%, respectively. The retention rate decreased with time and reached 43% in 5 years. Younger age of onset was a significant variable affecting retention rate for 52 weeks (p = 0.044), whereas fewer concomitant AEDs were significantly associated with being seizure free for 26 weeks (p = 0.0006). AEs were reported in 24% (36/147) of patients. The number, mechanism of action, or drug load of the AEDs did not predict the development of AEs; however, blood concentration of ZNS was significantly higher in patients with AEs (p = 0.0011) than in those without AEs. ZNS is a well-tolerated and effective AED in daily clinical practice, and several clinical factors may predict the efficacy and tolerability of ZNS.