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Hi,
During bioavailability study in rats, from oral and IV group, do we
need to collect the blood from only one site i.e either vein or artery?
or can it differ between groups .i.e for oral Vein and for IV group
artery.
I wish to know whether any difference will be there between
venoartrial drug concentrations.
Thanks in advance and with regards,
Sharath
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The following message was posted to: PharmPK
Hi Sharath,
There can be arteriovenous differences. How much of a difference depends
on the compound, rate of infusion/distribution.
Check out papers by WL Chiou, G Lam et al.
D Verotta in Br. J Clin Pharmacol 1994
M Weiss in J Pharmacokin Biopharm 1984
Susan Shoaf
OPDC
Rockville MD 20850
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The following message was posted to: PharmPK
sharath kumar wrote:
>
> Hi,
>
> During bioavailability study in rats, from oral and IV group, do we
> need to collect the blood from only one site i.e either vein or
artery?
> or can it differ between groups .i.e for oral Vein and for IV group
> artery.
>
> I wish to know whether any difference will be there between
venoartrial
> drug concentrations.
Dear Sarath,
Many drugs have large arterio-venous concentration differences. The
difference is larger for drugs with high distribution volumes and those
administered in ways that produce rapidly changing blood concentrations
(e.g. intravenously).
Peripheral venous blood is blood coming out of an organ and provides
information about the kinetics of the drug in that organ (e.g. an arm in
many clinical studies, or the head if you are using a short jugular vein
catheter in rats). Many clinical studies comparing drug effect with arm
venous blood report effect compartment half-lives that reflect the
difference between target organ equilibration and arm equilibration.
Venous blood concentrations can be difficult to interpret from a
physiological perspective! I would not advise using different sampling
sites for different groups in a bioavailability study for this reason.
If you are using a long jugular vein catheter in your rats, be aware
that central venous blood can be even more difficult to interpret. If
the catheter is advanced in a caudal direction it can actually pass the
right atrium into the posterior vena cava where it can sample blood
mixed with "extracted" blood coming back from the liver. This will
cause significant over-estimates of clearance.
If you want to take this further, Bill Runciman and I tried to summarise
the issues regarding where to sample blood from in a kinetic study in an
old review:
Runciman WB, Upton RN. Pharmacokinetics and pharmacodynamics - what is
of value to the practising anaesthetist. Anaesthetic Pharmacology
Review 1994; 2: 280-293.
Regards, Richard Upton
--
Dr Richard Upton
Principal Medical Scientist/Senior Lecturer
Discipline of Anesthesia and Intensive Care
Royal Adelaide Hospital/University of Adelaide
North Tce, SA 5000, Australia
richard.upton.at.adelaide.edu.au
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