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Has anyone conducted a clinical study measuring test compound in red
blood cells as well as plasma?
What was the rationale for measuring drug in rbc?
Was there good information derived from such an approach?
Thank you for any help.
Charlie
Charlie Brindley (KinetAssist)
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If you look at the blood to plasma ratios if = 1, then safe in analyzing either blood
or plasma
If greater than one, I would develop a "blood assay", if less than one develop
"plasma assay".
Can calculate estimate either from blood to plasma ratios.
Stanley Cotler
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Hi Charlie,
If a drug enters the erythrocytes and binds to erythrocytes proteins,
this will affect the ratio of total drug in blood/unbound fraction.
Examples are immunosuppressants and ribavirin. For the latter, entrance
in erythrocyte and in other cell types (mediated by es-type
equilibrative nucleoside transporters, is thought to be the reason for its high Vd.
This reference might be useful: Bioanalysis: 2010: Vol. 2, Issue 11, Page 1791-1796.
I hope this helps.
Regards
Stefano
--
STEFANO PERSIANI, Ph.D.
Director
Translational Sciences and Pharmacokinetics Department
ROTTAPHARM | MADAUS
R&D Division
Rottapharm Spa
Via Valosa di Sopra, 9
20900 Monza - ITALY
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The following message was posted to: PharmPK
Charlie:
I would check out what is available for sirolimus (rapamycin). There are
three fundamental reasons for analyzing blood instead of plasma: 1)
bioanalytical/stability issues, 2) the blood forms a distinct compartment
that better reflects the exposure of patients to the drug, and/or 3)
consistency with previous work. The latter reason again illustrates the need
to develop a solid bioanalytical technique early in development.
Chris
Christopher J. Kemper, Ph.D.
Pharma Navigators, LLC
DMPK/Bioanalytical Consulting
Alliance Management/Business Analysis
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I have not but lithium studies have examined this
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Hello Charlie,
The best reason for measuring a compound in red blood cells (RBCs) is
that certain compounds bind very strongly to RBCs and are not found
unbound in the plasma to any extent. Inhibitors of carbonic anhydrase
or any compounds that bind to carbonic anhydrase or other enzymes found
on the RBC may be unmeasurable in plasma but measurable in whole blood
or in RBCs. Most investigators use whole blood rather than RBCs. You
would want to measure the concentration in red blood cells at some point
to determine that is where the compound is bound, but whole blood is
easier to use than isolating red blood cells and accurately separating
them from every patient.
Best of luck,
Chris
Christopher Town, PhD
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I would be careful about that since you have a sink or depot even with a
ratio of 1
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Thanks to all responses regarding measurement of drug in RBCs.
Our drug is lipophilic (Log P 5.6) and B/P of 2.7 in monkeys (not measured to
date in human).
The bioanalytical assay in plasma should be adequate for measurement in FTIH study.
PK in mice, rats, dogs and monkeys has been carried out in plasma.
CL is low compared to hepatic blood flow (hepatocytes indicate limited
hepatic metabolism) and distribution volume is large (manifested as long
half-life in all sepecies).
Should we develop a blood assay in man rather than a plasma assay (given
that blood assay could be more problematic)?
Charlie Brindley
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Charlie,
When you say PK in plasma in animal do you mean also TK?
Have you completed all your TK and PD studies in all toxicological and
pharmacological species (rats, dogs, monkey, etc.)?
If the answers are yes, I would go ahead with the plasma assay for FTIH
as well. The top doses for FTIH will be selected based on animals
exposure determined at NOAEL and decision to move to the next higher
dose cohort, will be made (in addition to safety and tolerability) on
human exposure. Therefore exposure should be determined in the same
matrix in animals and humans. If different matrices are used, starting
dose selection and prediction of exposure in the next cohorts will be
cumbersome.
What we usually do is to run beforehand and In Vitro plasma protein
binding and blood cell partitioning study using blood and plasma from
mice, rats, dogs, monkey, and humans to select the optimal bioanalytical
method (plasma vs blood) and calculate fu to allow normalization of
exposure at pharmacological and toxicological doses between animals and
man to be used (among other things) for FTIH dose selection.
Best
Stefano
STEFANO PERSIANI, Ph.D.
Director
Translational Sciences and Pharmacokinetics Department
ROTTAPHARM | MADAUS
R&D Division
Rottapharm Spa
Via Valosa di Sopra, 9
20900 Monza - ITALY
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The following message was posted to: PharmPK
Hi Stefano
Note there is no scientific difference between TK and PK.
Steve
--
Professor Stephen Duffull
Chair of Clinical Pharmacy
School of Pharmacy
University of Otago
PO Box 56 Dunedin
New Zealand
E: stephen.duffull.-a-.otago.ac.nz
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Charlie: I have worked on a large NDA program of PK studies using whole blood
{2000 samples} , since ~90% of the drug was in the red cells. It was a carbonic
anhydrase inhibitor. The difficulty at that time was the assay sensitivity by
HPLC and UV detection. We needed to use the whole blood for that reason. The
major problem with using whole blood as the medium is that unlike plasma you
cannot freeze it. You have to keep the whole in the fridge and there is a
limit to the storage time you have prior to assay. Given the advent of
LC-MS/MS technology much higher sensitivity nowadays can be achieved in
plasma.
I would recommend that a plasma assay be developed and used.
hope this helps,
Angus McLean
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It's all a matter of amplitude
[or Dose. More MM - db]
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The following message was posted to: PharmPK
Hi
I agree that there is no scientific difference between TK and PK.
However, TK and PK studies (apart from being conducted at different
doses) are designed to answer different questions.
TK studies are conducted with a limited number of collection time points
(usually up to 24 h from dosing) to provide proof of continuous exposure
(Cmax and AUC) during tox studies, presence of gender differences, dose
and time dependency, relationship with toxicology findings, assessment
of relevance of the animal species selected. No other PK parameters are
usually calculated and PK analysis is usually conducted by
non-compartmental methods.
PK studies (including FTIH) are conducted using a much greater number of
time points (sometimes up to several days after dosing), disposition
parameters are calculated and compartmental PK analysis can be
performed.
The top dose in a FTIH study is usually selected based on exposure
observed in animals at NOAEL as determined in TK studies and unless
blood/cell partitioning data are available, prediction of exposure in
humans plasma based on exposure in animal blood, could presents
uncertainties and would require extensive justification to be accepted
by regulatory agencies and Ethics Committees.
If TK studies have been performed in plasma and no data on blood cell
partitioning are available in animals and man, I would use the same
matrix in humans and the one used in animals.
If blood cell partition studies provide indication of extensive
distribution in blood cells and binding to erythrocyte binding you might
consider Dried Blood Spot sampling but this choice should have been made
earlier in the drug development program.
Best
Stefano
STEFANO PERSIANI, Ph.D.
Director
Translational Sciences and Pharmacokinetics Department
ROTTAPHARM | MADAUS
R&D Division
Rottapharm Spa
Via Valosa di Sopra, 9
20900 Monza - ITALY
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The following message was posted to: PharmPK
Hi Stefano
> However, TK and PK studies (apart from being conducted at different
> doses) are designed to answer different questions.
> TK studies are conducted with a limited number of collection time
> points (usually up to 24 h from dosing) ...
I hear the term TK used and accept that these studies may have different
goals - but realistically this is just a study that has different goals
and it's still PK. That sampling and analysis techniques are different
is
not really relevant - sampling differs from phase 1 through phase 3 clinical
trials as does analysis techniques. That dose is different is also not
really relevant since doses in phase 0 to maximum tolerated doses vary
considerably as do exposure metrics in the general population.
=46rom this perspective isn't TKTD really just PKPD, but where the PD is
just an undesirable effect of the drug (any substance that elicits an effect
on the body). Since dose is a covariate in PKPD models then I don't see
how dose defines the difference in a meaningful way. To this end toxicology
is really just pharmacology studied by toxicologists. Please note I don't
dispute the need for toxicologists, as I do not dispute the need for
paediatricians (who look after humans who have small values of another covariate
[age] - however note that paediatricians still enlist the services of PKPD
not some other acronym).
I'm keen to reunite disciplines as being the same (to maximise learning
and understanding) rather than drive wedges between them that probably only
exist in our minds.
Regards
Steve
--
Professor Stephen Duffull
Chair of Clinical Pharmacy
School of Pharmacy
University of Otago
PO Box 56 Dunedin
New Zealand
E: stephen.duffull.-at-.otago.ac.nz
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