Analyzing excipient-related adverse events in antiseizure drug formulations

There have been several reports that switching formulations of antiseizure medications (ASMs) has been associated with a deterioration of seizure control, seizure relapse or increased adverse effects. Considering recent findings that excipients, namely purported inactive ingredients, may nevertheless exert biological effects, it is possible that the variation in adverse event profile of antiseizure drugs may be related to differences in excipients. To test our hypothesis, we constructed a new research tool to connect FDA-compiled adverse event reports to the excipient in the medicine. Analysis of adverse events to formulations of five different second-generation antiseizure drugs - gabapentin, lamotrigine, levetiracetam, oxcarbazepine, and topiramate - showed several significant associations between specific excipient in the formulations and an adverse event when compared to the same medicine formulated with other excipients. Epilepsy and seizure adverse events were associated with multiple excipients across gabapentin, lamotrigine, and levetiracetam formulations. A different group of excipients were associated with reports of hypersensitivity reactions including urticaria, rash, erythema, and Stevens-Johnson syndrome. Our study provides a novel approach to analyzing post-market surveillance reports by including excipients. It may be useful to clinicians when evaluating select patient groups that may be refractory to pharmacological treatment or experience worsening adverse events when switching formulations of the same antiseizure medicine.