RE: Time-varing covariate

Hi Siwei, If you are using an algebraic model (i.e. no differential equations), then you can simply include it in your equation: e.g. assuming that SBP is systolic blood pressure in your original data set: EFF=THETA(1)+SBP*THETA(2) If you have a differential equation model and you want the time varying covariate to have an effect that is not a step change, you will need to interpolate the covariate. Within your data set, you'll need a column for the next time and the next value of the time varying covariate. Using the same assumption that you have SBP in your data set as your time varying covariate, you will want to make two new columns to allow for interpolation: ID TIME NTIME SBP NSBP DV 1 0 1 110 115 5 1 1 2 115 112 3 1 2 4 112 108 4 Then to use your parameter, you will need code like the following in your $DES section to linearly interpolate: $DES ... ;; Current SBP CSBP = (NSBP - SBP)/(NTIME - TIME) * (T - TIME) + SBP ... The parameter T is the current time for the differential equation solver which will be somewhere between TIME and NTIME. TIME is an important column name for NONMEM. Thanks, Bill