Antiseizure Medications that Did Not Reach the Epilepsy Market: An Assessment of Factors Contributing to Their Failed Clinical Development Over the Last Three Decades

The EILAT Conferences on New Antiepileptic Drugs (AEDs), which have taken place biennially since 1992, have traditionally offered a forum for stakeholders from industry and academia to present updates on potential antiseizure medications (ASMs) in development. We reviewed publicly accessible data on compounds that were presented at EILAT conferences over this period but failed to reach the ASM market. The overarching aim was to determine the most likely reason(s) for terminating development and to provide potentially useful clues to improve the efficiency of ASM development in the future. We restricted our analysis to investigational compounds in clinical development that targeted common epilepsies. Of 56 such compounds, 15 reached the ASM market, 11 are still in development, and 30 had their development for epilepsy indications terminated. Compounds whose development was terminated include atimepazole, beprodone, cannabidivarin, carabersat, conantokin-G, dezinamide, elpetrigine, flunarizine, fluorofelbamate, ICA-105665, isovaleramide, JNJ-40411813, losigamone, naluzotan, padsevonil, pitolisant, ralitoline, remacemide, safinamide, soretolide, talampanel, tonabersat, T2000, T2007, valnoctamide, valrocemide, VX-765, zandatrigine, zuranolone, and 534U87. For most of these compounds, termination of development occurred during phase 1 or phase 2. Unfavorable pharmacokinetic properties, such as short half-life or high drug–drug interaction potential, were a common likely cause of early termination. Overall, the most common reason for terminating clinical development was lack of efficacy, possibly related, at least in some cases, to use of suboptimal trial designs. Review of preclinical data suggested that, for many compounds, suboptimal clinical efficacy was unlikely to be primarily explained by their mechanism of action. In some instances, failure to pursue an epilepsy indication could be explained by prioritization of development for other neurological or psychiatric conditions. This may reflect the perception of the drug market for common epilepsies being relatively crowded, and only attractive for compounds with outstanding safety or efficacy advantages over existing medications.