Trying to fix the PK parameters in a PK/PD model. How should constants be defined in the model text in the Phoenix model?
thanks
Hi Christopher,
you can freeze PK/PD parameters using the following syntax:
fixef(Ka(freeze)=1.234)
This has the meaning that the value for Ka is fixed and not estimated.
Does that help?
Bernd
Thanks Bernd, it works with the syntax provided although I the value is not fixed to the one specified in the model text, but it takes the inserted initial estimate and fix that value (e.g. in the model text
fixef(tvV(freeze)=10845)
is overuled by settting the initial estimate as 10000
But anyhow, Im able to contstrain my parameter, that was the aim here.
Christoffer
Hi Bernd (and all),
It seems not to work when I re-test. I Use the syntax provided but when running the model it is not picking up the freezed number. However, in the output the stderr are 0 for the 3 parameters I chose to freeze so it picks up the freeze process but not the values specified. What can this be caused by? do I need to do something in Intial Estimates tab?
Christoffer,
If you are in text mode, then what you see in the text should be what you get, it is possible to update these to the last run’s results by clicking the Accept all.. button onthe Fixed Effects > Parameter tab ? perhaps you did that inadvertently.
If you still see it then I would need to see the project/screen shot of settings to comment further, or you could email into support.
Simon
