Bioequivalence and Bioavailability Forum

Hi CECIF,

❝ […] the one parameter I have been struggling to get right in any way was Vd/F. Therefore I really need to ask what method bear uses to calculate it. […]

❝ or is it simply Vd/F=D/(AUC0inf*Ke)?

Exactly. The wonderful thing with open source is that you can perform a “whitebox” validation. With commercial software you can only perform a “blackbox” validation (rubbish in, rubbish out).

bear’s source code is available at
https://sourceforge.net/projects/yjlee-r-packages/files/bear/src/bear_2.8.3.tar.gz/download

Inspecting the script NCA.r you find in line 284
  VdFRef[j]<-Dose/(aucINF*ke)
and in line 520
  VdFTest[j]<-Dose/(aucINF*ke1)

Hope that helps.

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PS: The same formula is used in Phoenix/WinNonlin.
PPS: IMHO, the “volume of distribution” after an extravascular dose (if no i.v. dose was administered in the same study) bears [pun!] limited – if any – meaning. Since F is unknown, what’s the purpose of reporting V/F?