November 30 th 2005 Perkin Elmer, Seer Green UK. “….(these permeability) values are not equivalent (in value) and vary among labs, model compounds must be analysed by (both) methods to establish the correlation model for a given laboratory.”
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ie. don’t try to correlate your data with anyone else’s data and expect it to fit nicely. It has to be relevant to your work, using your compounds under your conditions.
“……correlation refers to the relationship established in a given lab using model compounds having well characterised (permeation) mechanisms.”
Kerns et al J. Pharm Sci 93 6 1440-1453 2004
People such as Avdeef have written prolifically on the subject
As for the theory, we were up to speed
But for more practical issues there are things like:
The size of the UWL does not depend on the volume flow. This prediction is correct only for vigorously stirred systems (Pohl et al 1997)
There is a UWL thickness corresponding to each molecule diffusing in the solution (Pohl et al 1998)
Thickness of the UWL does depend on the extent of stirring of the bulk solution, the layer becoming thinner with increased stirring (Karlsson and Arturrson 1991)Or how about Permeability
Donor and acceptor plates are incubated together for 12 – 16 hours (Millipore 2002)
….plates were incubated at 30oC for 2 hours or 15 hours (Sugano et al 2001)
…plates were incubated at room temperature for 2 hours with gentle shaking (Zhu et al 2002)
….6 – 15 hours (Ruell et al 2003)
….30 mins at 23oC (Avdeef et al 2004)
….4 hours incubation (Avdeef et al 2004)
The same goes for %DMSO, membrane constituents, sink conditions, buffers etc.
Millipore application note shows that they have looked into some of these variables
Not a luxury we can all affordBut it’s not just stirring, there are also things like…..
Without giving away all our proprietary information
Bumbling about in the dark
To find out if we are on the right lines
That’s why we are here
I sincerely hope that this will be the first of many opportunities to get together and talk science