Dear all, I have a dataset which shows 2-compt model with IV administration.After performing NCA, I obtained HL-lambda_z of approx 300h, although the last sampling point was 48h. This is because of the flatter terminal elimination phase. I am more interested in calculating the distribution half-life (alpha half-life) using non-compartmental analysis ( I have to report parameter esimates from NCA and not from compartmental modelling). In the setup of non-compartmental module, I am selecting the distribution phase instead of the terminal elimination phase in the slope selector section. I was wondering that by doing so am I violating any assumptions for non-compartmental analysis as we usually need to select the terminal phase for lambda_z calculation? Please find my data set as attachment. Thanks, Chetan [file name=dataset-20130825-4.xls size=24576]Certara | Drug Development Solutions (24 KB)
If you specify a time range to use, NCA will use all the points in that time range, so no assumptions are made about what points to use in the regression. So in the case of a user-specified range, for all models except NCA 220, NCA is just doing a log regression of the points in that range. That is, NCA just assumes exponential decay, and fits the natural logs of the concentration values by a straight regression line. For all models except NCA 220, it also assumes that the slope of that regression line is negative (lambdaZ is the absolute value of the slope), so NCA does not give a value for lambdaZ and all related parameters (including halflife) if the slope is positive. Linda
Chetan, I suppose I should add to Linda’s comment that if you are choosing the the distribution half life, then I would be very cautious in using any Lz dependent variables, obviously AUCinf is not a true AUCinf using such a selection. Similarly those parameters like Clearance that are calculated from AUCinf etc. Simon
Thanks for your suggestions. Regards, Chetan