Hello All,
I have a PK parameter that exhibits a negative trend with a particular covariate that can be been seen for the ETA vs covariate plot (shows a downward trend). In cases like these, it seems Phoenix NLME gives a negative estimate for the exponent along with a negative CV%.
Please see the hypothetical example below that illustrates the issue:
For example, for CL = tvCL*(BW/median BW)^dCLBW*exp(nCL), the estimate and CV% for dCLBW comes out to be negative.
Has anyone observed this before? Should I change the covariate model structure or it is ok this way?
Thanks in advance for your help.
Regards,
Charvi