Back to the Top
The following message was posted to: PharmPK
Dear colleagues,
Can you please enlighten me on the issue of randomization. While we
randomize the subjects according to treatment or drug assignment in a
BA/BE
study, is there a need to randomize the assay of the blood samples -
are
the samples of 1 subject be analyzed in random, or assay the samples
according to the blood sampling time or randomize also the subjects -
meaning which subject to assay in a given day (subject sequencing).
Thanks.
Joy
Back to the Top
The following message was posted to: PharmPK
Dear Joy,
S. Bolton and C. Bon;
Pharmaceutical Statistics.
4th Edition, Marcel Dekker (2004)
state at '11.4.2 Biovailability/Bioequivalence Studies' on page 327
'The blood is analyzed for each subject with both first and second
periods analyzed concurrently (the same day). To detect possible
analytical error, the samples are usually analyzed chronologically
(starting from the time 0 sample to the final sample), but with the
identity of the product assayed unknown (sample blinding).'
The reason behind this procedure is cross-contamination in
bioanalysis. Even state-of-the-art autosamplers show carry-over
between samples of about 0.5%, for older ones 1% is not uncommon.
If you randomize your samples, it's possible to analyze a blank
sample just after a peak sample, which would screw up your results.
In a BE study the 'best' sequence (with the least bias introduced
by analytical carry-over) would alternate samples from periods of
the same subject.
This naturally apllies only to a BE study (where we assume somehow
similar concentrations at the same time points in the same subject);
for a study on the absolute BA (or a PK study) different rules may
apply: just keep sample carry-over in mind.
Best regards,
Helmut
--
Helmut Schutz
BEBAC
Consultancy Services for Bioequivalence and Bioavailability Studies
Neubaugasse 36/11
A-1070 Vienna/Austria
tel/fax +43 1 2311746
http://BEBAC.at Bioequivalence/Bioavailability Forum at
http://forum.bebac.at
http://www.goldmark.org/netrants/no-word/attach.html
Back to the Top
The following message was posted to: PharmPK
Dear Joy
Generally in a BA/BE study, the plasma samples of one subject of all
the periods are analysed all together and in a sequence in which the
blood samples were corrected. If this is not possible then, you can
analyse the subject samples of each period separately but you need show
statistically that there is no period effect.
Ideally, the subject samples are coded and the analyst doesnot know the
ID of the subject sample.
I think this would help
Regards
Dr. Tausif Ahmed
India
Back to the Top
Dears,
In conducting bioavailability and bioequivalence studies, we usually
collect the blood samples from the subjects in vacutainers containing
K3EDTA as an anticoagulant. Now my doubt is, during bioanalysis, is
there any interference of the K3EDTA with the drug (plasma). If "YES",
how far it is. There are so many other anticoagulants are available,
but we are not using them always. OR is there any particular
specifications that this specific anticoagulants can be used for
specific types of drugs.So please clarify my doubt.
Regards
Bollu Prasad
Back to the Top
The following message was posted to: PharmPK
Hi Prasad,
As per my knowledge K3 EDTA does not reacts with
majority of drugs or metabolites in blood. The main
reason to use K3 EDTA vacutainers is its low cost,
easy availability and no specific storage problems.
Before year 2000 the commercial availability of K3
EDTA vacutainers in India was very less and you have
to import it from other countries and i believe still
we have to import it. The cost involved was very high
and to save the time and money we use to prepare the
solution (K3 EDTA salt easily available) and
distribute the small equal amounts (50uL) to ria vials
before adding the blood and then centrifuging it for
plasma.
Then slowly to avoid tedious process, to get more
accurate results and to simplify the blood withdrawals
from volunteer the above process was switched over to
vacutainers.
In addition to above history i believe the below
information may be useful to you.
EDTA works as an anticoagulant by chelating all the
calcium contained in blood. Calcium is needed for
coagulation to occur; without calcium blood will not
clot. The calcium levels needed to stop clotting are
low enough to kill someone, so EDTA is only used as an
anticoagulant outside the body
The sodium or potassium salts of EDTA (K2EDTA, K3EDTA,
Na2EDTA) are used in Vacutainer tubes. This means
levels of these ions are increased, and detectable
levels of calcium and magnesium are decreased. For
this reason many clinical chemistry tests are not done
using plasma from EDTA tubes
Citrate. It gets rid of the calcium, but not as
strongly as EDTA. Correct proportion of this
anticoagulant to blood is crucial because of the
dilution.
Heparin has the advantage over EDTA as an
anticoagulant, as it does not affect levels of ions
(such as calcium). Heparin can interfere with some
immunoassays used for estimation of drugs, however. As
lithium heparin is usually used, a person's lithium
levels cannot be obtained from these tubes and i
believe the cost of these vacutainers is high when
compared to others and storage of vacutainers before
collecting the blood.
regards,
nageshwar
PharmPK Discussion List Archive Index page
Copyright 1995-2010 David W. A. Bourne (david@boomer.org)