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I would like to know what is the minimum RSQ value that Phoenix look for before it stops calculating T1/2 or Cl parameters. What is the accepted RSQ (R2) value for GLP or non-GLP PK studies for PO and IV dosing?
Thanks in advance.
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The following message was posted to: PharmPK
I am guessing you are speaking of Phoenix WinNonlin; I'd suggest Support or the User Forum (www.pharsight.com/extranet) for a software specific issue like this in the future.
By default WinNonlin does not have a minimum Rsq for t_half calculations; it's goodness of fit is to select those points after Cmax that give the best fit for apparent ELIMINATION.
If it cannot find such a fit, e.g. an ascending slope or insufficient points then it won't be able to extrapolate AUC to infinity and therefore will not calculate T_half or Clearance (for the latter you'll also need to give it a Dose amount).
Once calculated you may apply column transformations filters to remove those parameters that exceed your own SOPs' guidelines e.g. AUC percentage extrapolated greater than 20% or you can look to the optional AutoPilot module which has much greater built in logic for these sort of business rules.
There is also recorded presentation available http://pharsight.com/events/eventsonline_archive.php#replay_016
(I'll leave others to comment on their 'guidelines' for rsq-adj., mine personally would be to aim for greater than 0.85)
Best regards, Simon.
Senior Scientific Consultant
Pharsight- A Certara(tm) Company
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