Physiologically Based Pharmacokinetic/Pharmacodynamic Animal-to-Man Prediction of Therapeutic Dose in a Model of Epilepsy

Animal-to-man extrapolation and therapeutic dose prediction are illustrated with two molecules designed to treat epilepsy. Synaptic vesicle protein 2A (SV2A) is the primary molecular target for their anticonvulsive effect, but additional mechanisms may also contribute. Brivaracetam (BRV), currently in phase 3 of clinical development, was used as the benchmark compound. A pharmacokinetic/pharmacodynamic model was built in NONMEM, relating the brain tissue concentrations of BRV in mice and the proportion of animals protected against convulsions in the pharmacological model of audiogenic seizures. Brain concentrations were linked with ex vivo binding to predict brain SV2A occupancy. A physiologically based pharmacokinetic model was developed for predicting BRV concentrations in human plasma and brain tissue. Predicted plasma profiles were in good agreement with observations. Predicted human brain concentrations of BRV and the mouse ex vivo binding pharmacokinetic/pharmacodynamic model were used to extrapolate brain SV2A occupancy at the human therapeutic dose. Secondly, for another compound also exhibiting selective affinity for the same target, similar pharmacokinetic/pharmacodynamic models were built from audiogenic seizure mouse data. Various dosing regimens of the new compound were simulated in order to reach the same brain SV2A occupancy as for the reference compound. These estimations support early development. Assumptions and limitations of the approach are discussed.