They have actually fit curves for SERT occupancy vs oral dose and vs blood concentration for each of the drugs tested. Am J Psychiatry. 2004 May;161(5):826-35. Serotonin transporter occupancy of five selective serotonin reuptake inhibitors at different doses: an [11C]DASB positron emission tomography study. Meyer JH1, Wilson AA, Sagrati S, Hussey D, Carella A, Potter WZ, Ginovart N, Spencer EP, Cheok A, Houle S. Abstract http://www.ncbi.nlm.nih.gov/pubmed/15121647   The full paper is availabl