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Hi,
There’s an ongoing debate in our department about which volume parameter is most appropriate to
report from NCA. For a single dose extravascular or IV input, which one is most likely to be a)
accurate or b) useful?
One argument is that the Noncompartmental analysis of Vss is incorrect when clearance is nonlinear.
The other is that Vz is a meaningless parameter and Vss is marginally better as it indicates total
volume.
I’ve looked at previous discussion threads about NCA volume reporting but I haven’t seen a consensus
about volume reporting. Any advice would be great.
Thanks,
John
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Dear John -
The following reference might be of use. Pharmacokinetics is an applied science. So it all depends
on what you intend to do with the parameters. If its simply for sake of generating a cell in a table
its doesn’t matter which volume you report. If the intention is to use these parameters to derive
dosing - then you will need to do what is useful. Vz doesn’t cut it. Unfortunately most of the
volume of distribution parameters in our product labels are Vz. Good that no body reads them.
1. J Biopharm Stat. 2001 Nov;11(4):373-5. Vz, the terminal phase volume: time for its terminal
phase? Gobburu JV, Holford NH.
Comment in J Biopharm Stat. 2006;16(1):123-4; author reply 125-6.
Trust me this topic will be discussed perennially....
Joga Gobburu
University of Maryland
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