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The following message was posted to: PharmPK
Yes Tom, your comment is very important. There is such a thing as physiology -
human or animal. And when anything is administered IV, we still need to take
into account both the input function (bolus, fast infusion, slow infusion), as
well as the site of infusion and the pathophysiological state of the subject.
Even the administration of a drug as a real bolus (2-5 seconds) may result in
a different distribution into the vascular space when this administration is
through a central line, antecubital or in the veins the hand. The individual's
blood pressure and other physiological factors also need to be taken into
account.
All this becomes very obvious (and very visible) when you have a patient in an
MRI, administer a contrast agent and measure the patient's blood flow and
perfusion. Using fast Dynamic Enhanced MRI (DEMRI) and data acquisition every
1-3 seconds illustrates very well the differences in blood flow - and hence,
in the distribution of any drug present in blood that is administered in the
same manner as the contrast agent.
Professor Walter Wolf, Ph.D.
Distinguished Professor of Pharmaceutical Sciences
Director, Pharmacokinetic Imaging Program
Department of Pharmaceutical Sciences, School of Pharmacy
University of Southern California
1985 Zonal Ave., Los Angeles, CA 90089-9121
E-Mail: wwolfw.at.hsc.usc.edu
Telephone: 323-442-1405
Fax: 323-442-9804
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The following message was posted to: PharmPK
We did some work on this with bolus doses, some 15 years ago, in humans and
in sheep. In fact the difference between sampling sites accounted for what
was then believed to be acute induction of tolerance to barbiturates.
In the periphery, venous blood may well represent concentrations in the
drained tissues to a greater or lesser extent.
Tom T
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)