Identification of adverse reactions that can occur on substitution of generic for branded lamotrigine in patients with epilepsy

Objective: The aim of this study was to characterize outcomes in patients with epilepsy who experienced adverse reactions on switching from branded to generic lamotrigine and who were subsequently switched back to the branded formulation. Methods: This case-series analysis used data frompatients identified through a survey of Ontario pharmacists, where Health Canada adverse-reaction forms submitted to pharmacists by physicians were retrieved, and from a physician chart audit and survey. Data from male and female patients with epilepsy who experienced an adverse reaction on switching from branded to generic lamotrigine and thus were switched back to the branded formulation were included. Results: The pharmacists' survey indicated that 11 of 14 retrieved adverse-reaction forms described patients with epilepsy who experienced loss of seizure control when generic lamotrigine was substituted for branded drug. Seizure control was regained in 8/10 (80%) patients with reported outcomes when they were switched back to the branded drug. Based on data from the physician survey response rate, 130/544 [24%1], 5/95 (5%) reported filing a Health Canada adverse-reaction form requesting that a patient be dispensed branded lamotrigine rather than the generic formulation. Six physicians provided data on 9 patients who experienced adverse reactions on a brand-to-generic switch, 8 of which were due to loss of seizure control. Seizure control was regained in all but 1 case on a switch back to the branded drug. Conclusions: The results of this small case-series investigation suggest that some patients may experience loss of seizure control when generic lamotrigine is substituted for the branded formulation. The degree of risk was not assessable based on available data, which are merely suggestive because of the observational nature of the study.