Target Occupancy Study (TOS), page-12

This correspondence was dated march 2018:

The study was designed to assess the pharmacokinetics of Xanamem, and therefor measured the CSF Xanamem concentrations and compared those to plasma. We could have done CSF cortisol levels but that does not accurately measure the intracellular cortisol, which is the target concentration we are after. To more accurately estimate intracellular cortisol levels, an enzyme occupancy study is required and we are making good progress in initiating such a study. Its technically proved difficult to do until quite recently.