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The following message was posted to: PharmPK
We need to do a mass balance study with C14 labelled compound in
normal and Long Evans rats. We need the information for a Phase II
IND/IMPD filing . We are a little confused when we discuss with the
different CROs regarding the study design, pricing etc. One issue is
that we need the information for getting biodistribution/mass balance
in rats. Another issue is that the information will be used for
human studies. I would like to get some clarifications on these.
Thanks and regards
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Without knowing much about your candidate compound, the therapeutic
target and dose regimen I will attempt a brief explanation that will
hopefully be sufficiently useful.
The design you describe involves normal and Long Evans rats. If by
normal you mean Sprague Dawley rats, these rats are albino and
without pigment in skin and the eyes. The Long Evans rats do have
pigment in these tissues. In a mass balance or tissue distribution
study the drug disposition in each species may be identical but a
difference may be demonstrated when skin and eye exposure is present,
it will be low or undetectable in the albino rats but may be evident
in the pigmented rats depending on the properties of the compound. If
there is a longer exposure in pigmented rats, is important to know
the amounts and extent when planning human studies. The use of
pigmented rats is there to provide data for dosimetry calculations
needed to estimate human exposure of the compound in clinical studies
when it has been shown that the drug is positive for skin and eye
exposure and the duration is known.
There are two types of studies you will need, mass balance and tissue
distribution studies. The studies in the albino rats can be short
term with the length depending on the PK and metabolism of your
compound and can be run a week or less. The studies with pigmented
rats typically overlap and run out 2-4 weeks longer to assess the
exposure in pigmented areas. I will be happy to provide more
information if you want to contact me directly as our company does
provide this service as well.
Karsten A. Holm, Ph.D.
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