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i am not quite sure of how pharmacokinetic modeling is done when
concentration results are expressed as %ID/g (percent internal dose per
gram). 1. is the dose assumed to be 1.0 (100 internalized dose)? 2.
if not, how is the dose expressed? 3. does the mCi dose come into
play somewhere? using %ID/g throughout the analysis does create some
rather difficult unit conversions which make some parameters either
undefined or just not calculatable. I would appreciate a reference as
to the methodology also. thanks in advance
[Concentration units = %ID/g, dose = 1.0 (IV ?), distribution
volume(size) term in gram - db]
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suggesting that a message Nick sent to PharmPK (and sent out) was
infected with a virus. Nick assures me that he is virus free ;-) and I
believe that with moderation and no attachments or mime allowed in
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Here is a reference where I believe the units are in percent of
injected dose per g and the model accounts for the radioactive decay.
Odom-Maryon TL, Williams LE, Chai A, Lopatin G, Liu A, Wong YC, Chou J,
Clarke KG, Raubitschek AA.
Pharmacokinetic modeling and absorbed dose estimation for chimeric
anti-CEA antibody in humans.
J Nucl Med. 1997 Dec;38(12):1959-66.
PMID: 9430477 [PubMed - indexed for MEDLINE]
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Hello Tim:
Our group has worked with radioactive tracers
(usually antibodies) for some years. I would advocate not using
%ID/gram as a modeling parameter as it leads to a number of
complications. For example, there is no conservation of activity in the
total system. Instead, you should use %ID/organ in the analyses. There
are exceptions: blood and urine samples will always be in units of
%ID/ml and must be scaled to the total activity in those systems. For
blood, we used an unknown blood volume or the patient specific blood
volume calculated via patient parameters. In the case of urine, the
total volume excreted should be measured for each sample that is
assayed.
With the fluid exceptions given above
understood, you should realize that, in patients, the activity is going
to be in natural units of %ID/organ. This is determined with gamma
camera or SPECT images. Thus, organ activities are naturally in
%ID/organ. Likewise, at t = 0, the sum of %ID/organ over all the major
systems should add to 100%ID.
The article given by Professor Newman is an
example of our work. We have also done animal biodistribution modeling
using %ID/organ. We have not published extensively on the latter,
however. All of our analyses involved ADAPT II software.
Let me know if you have any questions.
Best wishes.
Larry Williams.
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