Daniel,Back to the Top
Proteins and protein-bound drug remain equally in both plasma and
serum. If you do a liquid-liquid extraction or any other method you break the
protein-drug bonds and compounds, so in both plasma or serum you will
quantify total rather than unbound drug. To measure the free drug
fraction you must use an ultrafiltration, or other such method, to obtain and
then quantify it with HPLC.
Rosario Calvo Duo, PhD
Department of Pharmacology
Faculty of Medicine
University of the Basque
Leioa, Vizcaya 48940
tel: +34 946012761 UTC+1hour
fax: +34 944800128
Dear Daniel,Back to the Top
Few months before there was some discussion in this group about using
serum or plasma, you can look at the archive and get the information.
"Are these methods of extraction able to separate drugs from protein
binding? What are the evidences of it?"
You can obtain this information while doing Extraction Efficiency
experiements. Spike the same conc. of the compound to plasma/serum and
the buffer and extract with the suitable solvent, the area counts in
both the samples of same conc. should be same. This answers whether one
can separate almost all the drugs from protein binding.
"Which sample is more appropriate to TDM: serum or plasma?"
I feel one can use any of the above only thing the compound studied
should not be affected by coagulating factors.
Obtaining plasma will be easier and volume wise will also be more.
Hope this helps,
[You can start at the archive search page
http://www.boomer.org/pkin/simple.html - db]
Dear Group,Back to the Top
There are several reasons to prefer plasma over
serum in bioanalysis which I listed below.
1.Time saving: Plasma samples can be centrifuged
directly after sampling,unlike serum,in which you need
to wait for coagulation
2.Higher yield: 15-20% more in volume of plasma than
of serum can be separated out from the same volume of
3.Prevention of coagulation-induced interferences: The
coagulation process changes the concentrations of
numerous constituents of the extracellular fluid
beyond their allowable limit
3a. Increase in the concentrations of platelet
components in serum as compared to plasma (e.g
which becomes crucial especially when you do the
simultaneous estimation of biochemical parameters for
instance Pharmacokinetics in Acute renal failure
3b.Decrease in the concentration of constituents in
serum as a result of cellular metabolism and
coagulation process (glucose,Total protein,platelets)
4.Also certain constituents should only be measured in
plasma to obtain clinically relevant results for e.g
Hope this helps
S Syed Mustafa,
Drug Metabolism & Pharmacokinetics,
Dr Reddy's Research Foundation,
Bollaram Road, Miyapur,
In general, there is little difference between serum and plasma, exceptBack to the Top
for certain analytes. For example, LDH, potassium and phosphate are
higher in serum than plasma, because of release of these constituents
from cells during clotting. Protein and globulins are higher in plasma
than serum, because plasma contains fibrinogen.
1. The disadvantage with serum is that the samples can take a while to
clot, therefore if the study involves large number of samples to be
taken within a short period of time and stability of the analyte is a
problem, collection into heparin (green top tube) is advised to
expedite sample handling.
2. Secondly, in routine protein binding studies, one evaluates the
percent of binding in plasma as the protein content of plasma is higher
than that of serum.
Malaria research lab, M9/02,
Tel (lab) +46 8 51773358
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