Re: Variability on infusion duration

On 8/5/2020 12:18 PM, Patricia Kleiner wrote: > Dear all, > > I am developing a PK model for a drug administered as a long-term infusion of 48 hours using an elastomeric pump. End of infusion was documented, but sometimes the elastomeric pump was already empty at this time. Therefore variability of the concentration measurements observed at this time is quite high. To address this issue, I try to include variability on infusion duration assigning the RATE data item in my dataset to -2 and model duration in the PK routine. Since the "true" infusion duration can only be shorter than the documented one, implementing IIV with a log-normal distribution (D1=DUR*EXP(ETA(1)) cannot describe the situation. > > I tried the following expression, where DUR ist the documented infusion duration: > > D1=DUR-THETA(1)*EXP(ETA(1)) > > It works but does not really describe the situation either, since I expect the deviations from my infusion duration to be left skewed. I was wondering if there are any other possibilities to incorporate variability in a more suitable way? All suggestions will be highly appreciated! > > Thank you very much in advance! > Patricia