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To the group:
How often do you do serum sampling for PK studies? Most of the PK
studies I see is with plasma sampling. Do you have heparin in your
plasma samples? Why is heparin not desired sometimes? Any responses
would be greatly appreciated.
Chandrani Gunaratna
Chandrani Gunaratna, Ph.D.
Senior Research Scientist
Bioanalytical Systems
2701 Kent Avenue
West Lafayette, IN 47906
(765)463-4527
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this a very "wide open" question. serum sampling strategy is
dependent on the kinetic characteristics of the compound in question.
obviously to get adequately charactized the absorption and
distribution periods, one would want to sample more robustly during
the early time points. i would suggest a small pilot study before
developing a full protocol.
as far as the plasma vs serum issue is concerned, i have worked with
both. depending on what matrix you want, that will dictate the
addition of heparin or not to your sampling tubes.
let me know if i can help you further
tim cacek, pharm.d.
pharmacokineticist
adme consulting
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Sender: PharmPK.at.boomer.org
Reply-To: Prashant Bodhe
Mime-Version: 1.0
From: Prashant Bodhe
Date: Mon, 16 Oct 2000 00:10:58 -0400 (EDT)
To: david.-at-.boomer.org
Subject: RE: PharmPK Serum or Plasma Sampling?
Dear Members
The choice of serum or plasma depends on two
1. Properties of drug, (protein binding, etc)
2. Requirementts of analytical method (interference from
components of serum or plasma
However if none of these two facors are significant then the practise
of the lab undertaking the study governs.
It is easy to use heparin since it is readily available in both
powder and solution form. There are several other anticoagulants
which are sometimes required to be used. Most common are sodium
edetate, sodium citrate. [In case yo require further details of
amount to be used please mail me.]
In my experience heparin if used in excess (inadvertly) may cause
poblem either by hemolysing the blood sample or by causing
interference during the analysis. Later especially if the extraction
is in the basic pH, and detection in UV range.
So easy alternative is to use edetate
Dr. Prashant
---
Sender: PharmPK.aaa.boomer.org
Reply-To: "Morandini, Cristiana"
MIME-Version: 1.0
From: "Morandini, Cristiana"
Date: Mon, 16 Oct 2000 07:56:22 +0100
To: david.aaa.boomer.org
Subject: RE: PharmPK Serum or Plasma Sampling?
The following message was posted to: PharmPK
Dear Chandrani,
In the preclinical studies, we use to withdraw no more than 10% of the total
body blood volume/subject.
Heparine could affetc the plasma protein binding and also could interfer the
analysis of the compound.
Even if I never found these problems in the course of my work..
Regards
Cristiana Morandini
New Technologies Development Group
Bioanalysis and Drug Metabolism Dept.
GlaxoWellcome Research Center
Via Fleming 4 - 31135, Verona Italy
Phone: +39 45 9219102
Fax: +39 45 9218153
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Dr.Gunaratna,
A venous serum sample (cell-free component of clotted blood) is
the usual method of obtaining drug assays, but methods are being
developed for the assay of drugs in plasma and whole blood. However,
plasma concentrations may differ significantly from serum concentrations,
as aminoglycoside concentrations were 7.8% lower in serum versus plasma
in one study. (1) Other sources report that there is very little drug
binding to fibrin or other components of the blood clot, making serum
samples equivalent to plasma samples for the most part.(2)
Plasma samples can be obtained by preventing coagulation with
various agents including heparin and the calcium binding resins
EDTA, citrate and fluoride. The choice of the anticoagulant can
affect the assay results, and most clinical laboratories use serum
for drug assay analysis.(1,2)
Heparin in high concentrations has been shown to cause falsely
low concentrations of aminogylosides when assayed by microbiologic,
enzyme or radioenazymatic assays. This can occur when samples are
incorrectly obtained in heparinized collection not completely filled
with sample, or when drawn through heparinized intravenous catheters.
Although when flourscence polarization immunoassay or EMIT assay for
gentamicin or tobramycin is used, serum and plasma are interchangeable.
(1)
Mike Leibold, PharmD, RPh
ML11439.aaa.goodnet.com
References
1) Schumacher, G.E., Therapeutic Drug Monitoring, Norwalk, Appleton
& Lange 1995
2) Sadee, W., Beelen, G.C.M., Drug Level Monitoring, New York, John
Wiley& Sons 1980
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)