PD analysis without PK data

From: ksriram@ufl.edu Date: Thu, 10 Aug 2000 09:52:58 -0400 (EDT) Subject: PD analysis without PK data Dear NM users, I would like to have your opinion on how reliable the EC50 estimates of a drug would be if I fit PD data in the absence of PK data. here is the scenario: 60% of my data set has both PK and PD data. So fitting PK separately has given me good pop and individual parameter and inter ind and residual variability estimates. Now, by fixing these and just letting NONMEM choose the individual PK estimates that best fit the PD data, will the EC50s that I calculate to describe the other 40% of the data set (i.e only PD) be reliable? What statistics, if any, should I use, if this procedure works, to compare PK estimates in PK rich versus NO PK. Thanks, Sincerely, Sriram