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Dear all,
We have comparative study data of dried blood spot techinque (DBS) and
normal blood collection technique. In which in one technique we are
using whole blood on the other hand we are using separated plasma for
bioanalysis. So how can we compare both the data blood Vs plasma
concentration. Is there any correction factor applied for plasma or
blood? to make it comperable?
Regards,
Rahul Vats
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Hi,
The plasma concentration of a drug can be related to the whole blood
conecntration by the blood : plasma concentration ratio (a)
a = drug concentration in whole blood/drug concentration in plasma= Cb/C
Cb= C * a
I hope it helps to you,
Regards,
Vijender
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Dear Rahul,
We can establish a relation by the following equation:
Cb = Hct*Cr + (1-Hct)*Cp
Cb = conc in blood
Cp = conc in plasma
Cr = conc in red blood cells
Hct = hematocrit (a ratio of volume of red blood cells to volume of
blood)
This may be of help to you
L.V.Chakradhar,
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The following message was posted to: PharmPK
Dear Rahul,
The analysis to be performed depends on your data. You'll probably have
repeated measures, so make sure to perform a proper analysis of
variance. Performing linear regression on dried blood spot
concentrations versus plasma concentrations is not the way to perform
such an analysis.
I have typically seen a concentration-independent dried blood spot to
plasma concentration ratio when comparing dried blood concentrations
with plasma concentrations. If this ratio is not equal to 1 (a ratio of
1 means that plasma and dried blood spot concentrations are equal), you
should take into account that perhaps your analyte accumulates (or does
not accumulate) in erythrocytes. You should then also test the influence
of hematocrite level on the ratio. Furthermore, you should test whether
the concentration ratio is constant during a dosing interval and is
constant in the relevant concentration range.
Cheers,
Rob ter Heine
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Dear Rahul,
ideally you should get the same ratio for concentrations in blood and
plasma for all you sampling points. Cb:Cp should always be greater
than 0.5 (drug only in plasma not in blood cells, H around 0.5) and
can go up to above 2 or 3 when the drug strongly partitions into blood
cells. In case the ratio is different at different concentrations you
might have saturable binding in either blood cells or plasma, but this
is usually not the case. In future studies, when you sample only one
matrix, you can use this ratio to convert PK parameters based on
plasma into parameters for blood or vice versa (e.g. CLp/CLb=Cb:Cp).
Regards,
Markus
H Markus Weiss, PhD
Novartis Institutes for BioMedical Research
Translational Sciences - DMPK
CHBS, WSJ-210.4.25
Novartis Pharma AG, Werk St. Johann
CH-4057 Basel, Switzerland
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The following message was posted to: PharmPK
All,
Comparing dried blood samples to plasma concentrations does not
usually work,
according to folks at GSK who pioneered the technique of using dried
blood to
assay TK samples in toxicology studies. The issue that arises in drug
development is how to establish safety margins in humans based on such
data.
At a webinar where the technique was presented, they indicated that
"sometimes it works sometimes it doesn't". This isn't surprising, since
blood plasma partitioning is frequently concentration dependent. GSK
indicated that they were getting around this by using the dried blood
assay
for the clinical samples as well.
Dale
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Dear all
Thanks for explaining me in such a nice manner but i wanted to know
that if we have in house molecule PK data in rat plasma (technique
used SPE) so can we reproduce same pk parameter including AUC by blood
spot technique as in this technique they are using dried blood and can
convert it in to plsama pk parameter? or is there any plasma spoting
technique so that we can compare it directly plasma to plasma data of
our compound or should we reanalyse our in house compound in whole
blood to compare it blood spot technique?
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