, 2008 and Wilke, 2011) possibly due to drug accumulation or delayed neurotoxicity. No single preclinical safety testing strategy can apply to all compounds and identification of acute or chronic drug effects may be warranted Epigenetics inhibitor (Ferrero et al., 2005). Designing seizure

assessment studies requires a careful evaluation of multiple facets including pharmacology, pharmacokinetics/biodistribution, the target indication and patient populations, regulatory requirements/expectations, species specificity and projected clinical trial designs, to list only a few. Within an animal species, variations in susceptibility to drug-induced seizure need to be considered to determine the optimal group size. The incidence of CNS adverse events in prior

toxicology/pharmacology studies may inform on expected inter-individual variations and the group size and/or doses to be tested in the follow-up seizure liability study need to reflect this anticipated incidence. Typically, group sizes of 5–10 are used in rodents while 4–8/group is often adequate in non-rodents. The progression of clinical signs to seizure in animals is typically used to inform premonitory signs that are later used to halt dosing in clinical Integrase inhibitor trials. It remains that the presence and sequence of premonitory signs in animals may differ from that observed in humans and caution is recommended in the translational assumptions. When present, discrepancies between the progression of premonitory signs in animals compared to humans may be caused by differences in receptor binding affinity, cellular mechanisms, metabolism, biodistribution, just to name a few. Species specificity may also impact the clinical sign profile observed prior to seizure (e.g. lack of emesis in rats, high susceptibility to emesis in dogs). When convulsions are observed in prior non-clinical studies, the follow-up neurological safety pharmacology study may or not evaluate dose levels high enough to induce seizure. As the

objective of such follow-up study is to confirm the no observed adverse effect level (NOAEL) relative to seizure activity, an appropriate safety margin (e.g. 10 ×) is required but dose levels considerably higher than intended clinical nearly doses may not be relevant even when such dose levels were used in early dose range finding toxicology studies. Interactions with regulators reviewing the safety data may guide in selecting the most relevant non-clinical neurotoxicity testing strategy. When communication with regulators is not possible, scientific justifications (e.g. targeted indication, context of use) can be used to support design selection. The observation of moderate to severe tremors in a toxicology study may trigger neurological safety concerns and understanding the nature of those tremors presents value in completing the risk assessment.