[NMusers] Time-varying PK DURING the course of study

[Khaled Nm]

Dear nmusers,
 
I found it is difficult to account for age varying in PK parameter during the 
course of the study.
 
Is there any way on how to define icreasing age as a covariate in the NONMEM 
data file? A short example would be very useful for me.
 
thanks for your help.
 
khaled