Dear Raghava

Your oral data show 2 peaks. I therefore add one extravascular compartment and assumed a fraction of the drug goes via first absorption site and the remaining through the second one. A fraction must be between 0 and 1 and we have the inverse logit function that does that. ilogit(x)=exp(x)/(1+exp(x)) ; x between -infinity and plus infinity will give ilogit(x) between 0 and 1. That is why x must be normally distributed an not log normally distributed (see structural parameters).

Now when you have both oral and IV, we can estimate the bioavailability which is the fraction of the drug that goes systemic. This fraction is called ilogit(flogit) where flogit is normally distributed.

ilogit(flogit) is the fraction of the drug that goes systemic(between 0 and 1).

Now the real fraction that goes from the first absorption site is equal to the product of the fraction bioavailable multiplied by the fraction from the first site. The real fraction that goes from the second absorption site to Plasma is the bioavailability x by the fraction that goes to Plasma through the second site.

Now if you really have cross over and the time was reset to 0 as in your data set. It assumes that the IV and oral dose were given at different occasions and that there was a full washout between the two occasions.

If you reset the time to 0, you need to tell hat to the program and also washout need to be told to the program.

The fact that the time is reset to 0 can be handled by first putting the data by ID and then occasion and then time and when you have the second occasion tell the program to washout all the compartments.

This is done by first uncheck the sort input option (in run options) and then in input options select reset option.

I put 4 to 4 because I defined a column called reset and put 4 when I want the reset.

Let me ,know if you need further clarificaitons.

No reset if you consider different ID'S for IV and oral.

Best

Serge