Accounting for time-varying covariates on PK parameters in mrgsolve

[Ahmad Abuhelwa]

Attached is a demo example of a simple 1 compartment first-order absorption model to illustrate the issue. The bioavailability in my model (F_GUT) is time-varying within the same subject and is calculated based on duration of treatment; DAY in the input dataset. However, mrgsolve is not doing the right thing here as it still assumes F_GUT=1 for the second dose while it should be 0.6065307 as per the example I attached (i.e. The amount in the GUT should be DOSE * time-varying F_GUT but it is not this case here).

I am not sure if mrgsolve accounts for time-varying covariates? or coding F_GUT in the way presented here is not right? 

Thanks!