PharmPK Discussion - Flip Flop modeling

• On 12 May 2010 at 16:36:22, "Aline Fuchs" (Aline.Fuchs.aaa.biovail.com) sent the message
  

  
  Dear All,
  
  As a student, I am currently working on modeling some extra-vascular individuals PK data. (No IV reference available). Data show a Flip Flop kinetics.
  
  How is it possible to model such data?  Since the terminal phase seen is absorption, does the value Ke given by the software (phoenix WNL) is, in fact, Ka? When I chose initial estimates, should I assign values close to the real one (means: initial estimates Ka < initial estimates Ke)?
  
  And I also would like to know in which case we prefer to parameterize either by clearance and volume or by rate constant?
  
  Thank you to put me on the right track
  
  

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• On 12 May 2010 at 19:09:41, "Roger W. Jelliffe" (jelliffe.aaa.usc.edu) sent the message
  

  
  The following message was posted to: PharmPK
  
  Dear Flip flop:
  
    You decide which should be the faster of the 2 rate constants - Ka
  or Kel. If you should decide that Ka should be the faster, then write the
  differential equations so that Ka = Kel + X, for example. Then Ka will
  always be faster than Kel and you will have no flipflop. On the other hand,
  if you wish to use the opposite solution, where Kel is faster than Ka, just
  do the opposite and say that Kel = Ka + X. In this way you will select the
  solution you prefer to use.
  
  Very best regards,
  
  Roger Jelliffe
  
  

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