Bioequivalence and Bioavailability Forum

Dear Sir,

I have calculated Pk parameter by NCA modeling by using WinNonLin software but ratio of AUC0-inf to AUC0-t was less than 0.8 in some cases and Rsq is also less than 0.8 in those cases. This is when software automatically select the time points for the calculation of elimination rate constant (Lamda_z). After that i selected time points manually for calculation of Lamda_z in such a way that Rsq valule comes atleast above 0.8. Now ratio of AUC0-inf to AUC0-t is improved and CV% for AUC0-inf is reduced etc. These time points were selected after the Cmax and above the LOQ. But i don't know that is this right way to calculate these parameter. Is there any suitable technical or regulatory guideline for calculating these parameter (or selection of time points for Lamda_z calculation).

Best Regards