Impact of generic substitution on levetiracetam serum concentration-A prospective study in an outpatient setting

Switching patients from a branded antiepileptic drug (AED) to a generic is often challenging. Several studies have shown that considerable proportions of patients report deteriorated seizure control or increased adverse effects, enforcing a switchback to the original drug. Since tolerability and seizure control usually correlate with AED serum concentrations, we examined the fluctuation of levetiracetam (LEV) serum concentrations in patients with epilepsy before and after generic substitution.

This was an 18-week, naturalistic, open, prospective, two-center study. After a baseline period of 10 weeks, 33 outpatients on stable treatment with branded LEV (Keppra^®) either continued with this product or were switched overnight to a generic LEV preparation (1A Pharma) for an eight-week study period. Throughout the study, patients were monitored with bi-weekly LEV serum concentration measurements and seizure diaries.

16 out of 33 patients were switched to a generic LEV product. No switchbacks were seen. LEV dose, LEV serum concentrations, fluctuation index and concentration/dose-ratio (C/D-ratio) were not significantly different within-group (baseline vs. study period) or between-group. Large within-subject variability in serum concentrations was seen in both groups. None of the patients that were seizure-free before inclusion experienced seizures while on the generic LEV product.

Our results show equal fluctuation of LEV serum concentrations with branded LEV and the generic LEV. Most importantly, within-subject variability was much larger than the small, non-significant differences between brands.