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Hello,
I hope to use omeprazole as a phenotyping probe drug to give an
indication of CYP2C19 activity in cancer patients. Previously
omeprazole phenotyping has been carried out with oral omeprazole, but
there is the potential for variable absorbtion in my patients. Does
anyone know of any studies which validate the method of CYP 2C19
phenotyping using intravenous omeprazole with measurement of a
metabolic ratio in plasma at a single time point?
Many thanks
Simon Brown
Clinical Research Fellow
Dundee
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Omeprazole has a very rapid elimination, all your sampling needs to be
before 2hrs of dosing, while designing your studies to do phenotyping
you
need to draw quick and elaborate samples from 0-2hrs. I am afraid and
speculating that by doing an inhibition work using parenteral
omeprazole you
are defeating the purpose of CYP 2C19 as oral administration is a
pre-requisite for omeprazole presystemic effects.
My two cents....
Prasad Tata
Mallinckrodt, Inc.
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Dear Simon,
You might try Mephenytoin as a probe of CYP 2C19 instead and study the
urinary excretion ratio of 4-OH S-Mephenytoin over S-Mephenytoin in
urine.
Best regards,
Kees
Kees Bol, PhD
Director Clinical Pharmacokinetics
Kinesis Holding
Consultants in Drug Development
Lage Mosten 29
4822 NK Breda
The Netherlands
tel: +31 (0) 76 54 80 621
gsm: +31 (0) 65 31 26 153
fax: +31 (0) 76 54 21 777
kees.bol.-a-.kinesis-pharma.com
www.kinesis-pharma.com
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Dear Kees & Simon,
From what I can gather doing a survey on the medline, this drug
(mephenytoin) is rarely used as in-vivo probe for CYP2C19 phenotyping
nowadays, instead Omeprazole is used (though not that selective). The
reason may be in its adverse reactions.
Ahmad
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It is rather availability, at low doses (50 mg) mephenytoin
tolerability is no problem.
Prof. Dr. med. Uwe Fuhr, Institute for Pharmacology, Clinical
Pharmacology, Gleueler Strasse 24, 50931 Koeln, Germany
http://www.medizin.uni-koeln.de/institute/pharmakologie/Ag_fuhr2.html
Office: phone +49-221-478-5230
fax +49-221-478-7011
e-mail uwe.fuhr.-a-.medizin.uni-koeln.de
Home: phone +49-69-446976; +49-2681-988050
mobile phone +49-179-5002468
fax +49-69-94414738
e-mail uwe.fuhr.at.t-online.de
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