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The following message was posted to: PharmPK
Dear Memebers
I need your valuable suggestions on the following query.
Which concentration or concentrations of substrates can be used to
study the
CYP inhibition studies for respective CYP enzymes? Which is the ideal
way to
perform CYP inhibition studies?. Selecting an arbitrary concentration of
substarte (in excess) or determining the Km value and using the conc
at Km.
Thanks in advance
Regards
Mohd.Khalid Pasha
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Dear Mohammed,
When you are talking about "substrates", do you mean the CYP isoform
marker reaction substrates (concentrations ought to be close to Km )
or the concentrations of your test compound i.e. potential
inhibitor? (This you need to vary, otherwise you will not get IC50
and/or Ki values)
Also, it may be advisable to check the degree of (microsomal protein)
binding and recoveries in your experiments. Obviously, extensive
protein binding (or binding to apparatus) may give you incorrect
results. This is especially important if you are looking to make I/Ki
predictions to in vivo, just as PPB is.
From your mail it is not obvious which stage your compounds are at,
so it is difficult to say what the best assays would be. In early
screening stages (LO, early preclinical), medium- to High throughput
flourescence based assays are available to give a first indication of
CYP inhibition potential. These are relatively cheap and fast, but
are meant for comparison and ranking between cpds or cpd classes
only. If you need to outsource these activities, there are many
providers in Europe and the US.
If you need to address the issue in later preclinical stages, you
would need to do more detailed experiments involving well
characterised marker substrates of CYP isoforms in a good-sized pool
of human liver microsomes (some people even prefer to do this work in
human hepaotcytes). Again, this work can be outsourced to specialised
contract labs if you prefer not to do it "at home".
At any rate, there are FDA/EMEA guidelines and many papers
available, for example :
FDA Guidance for Industry Drug Metabolism/Drug Interaction Studies in
the Drug Development Process: Studies In Vitro
Draft Guidance for Industry: Drug Interaction Studies - Study Design,
Data Analysis, and Implications for Dosing and Labeling - 9/11/2006
Bjornson et al., DMD 31:815-832, 2003
Tucker et al, Pharm Res 18(8): 1071-80, 2001
I hope this has been of help!
regards,
Constance
DMPKORE
Dr Constance Hoefer
Marie-Curie-Str 6
85055 Ingolstadt
www.dmpkore.com
+49 841 9014540 tel
+49 841 9014542 fax
c.hoefer.-at-.dmpkore.com
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The following message was posted to: PharmPK
Your questions are broad, but the recent (released this month) FDA draft
guidance, Drug Interaction Studies - Study Design, Data Analysis, and
Implications for Dosing and Labeling, may provide the information you
seek. It can be found here:
http://www.fda.gov/cder/guidance/6695dft.pdf
Gene Williams, Ph.D.
Senior Clinical Pharmacology Reviewer
CDER/FDA
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The following message was posted to: PharmPK
Mohammed:
The FDA has two guidances that may be helpful:
http://www.fda.gov/cber/gdlns/metabol.pdf
http://www.fda.gov/cder/guidance/clin3.pdf
In addition, you may find this FDA website useful:
http://www.fda.gov/cder/drug/drugInteractions/default.htm
Sincerely,
Carol Collins
University of Washington
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The following message was posted to: PharmPK
I would suggest searching the literature as a first step - otherwise it
will be hard to justify your choices by referencing a email list group.
Regards,
David
David Foster, PhD
Lecturer
School of Pharmacy and Medical Sciences
Room P4-08
City East Campus
University of South Australia
Adelaide SA 5000
CRICOS Provider Number: 00121B
Phone: 61 8 8302 2055
Fax: 61 8 8302 2389
Email: david.foster.aaa.unisa.edu.au
[The links at the bottom of my course page at http://www.boomer.org/c/
p4/c17/c1702.html might be useful - db]
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The following message was posted to: PharmPK
Hi, There is plenty of literature available about CYP inhibition /
induction studies both
in microsomes and hepatocytes, by simple PubMed search.
You can find different probe substrates, their concentrations,
incubations etc.
Only thing is to select an appropriate probe for their specific CYPs.
Good luck,
Sripal
PharmPK Discussion List Archive Index page
Copyright 1995-2010 David W. A. Bourne (david@boomer.org)