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I also have a naive question: when you are doing pk studies, how do
you determine the sample size for each formulation you want to test?
Power analysis seems complicated to perform. Is there a magic number
for rats? Often when I read n=3 in the pk literature, I wondered if
that study was actually valid statistically.
Thanks,
Jin
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Hi,
I remembered the size was 4 at least!
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The following message was posted to: PharmPK
Estimating sample size is a good approach but you need a starting
point. In
discovery work, three samples per time point will work for this or you
can
refer to historical data for the same or similar compounds. Generally,
there
are restrictions on the volume of blood withdrawn at each point from
each
animal so while three samples per point will work you may need to add
more
animals to cover the needed number of time points.
If statistical comparisons are needed, once you get the initial data
you can
estimate parameters needed to compare to a second dose group with
specified
probabilities, as well as the variance and anticipated differences in
dose.
That analysis may suggest the need to increase the number of animals.
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Sorry I didn't make myself clear. When I said sample size for testing
each formulation, I meant the number of rats at each sampling time.
Thanks,
Jin
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The following message was posted to: PharmPK
Hi Jin,
As you may know, we have the guidance of bioequivalence from
authorities such as FDA in clinical bioequivalence studies, but not in
non-clinical studies. Then, humane for animals might often be more
emphasized than scientific rationale in non-clinical stuies.
Now, we need at least 3 samples to calculate standard deviation or
standard error. Therefore, I think 3 samples may be adopted in some
investigations.
Best regards,
Mitsuo Higashimori
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It should be not less than 5 in beginning of the studies. latter on
the number should be increased.
Dr zafar
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The following message was posted to: PharmPK
Dear Jin,
The number of animals used in pharmacokinetic studies should be large
enough to reliably estimate population variability. In the case of rats
and mice, tissue and/or blood sample size is usually the limiting
factor: analysis of the substance may require 1 ml or more blood, but it
is difficult to obtain multiple blood samples of this size from one
animal. As a consequence, a larger number of animals is required (3 - 4
per time point, 7 - 9 time points) when small rodents are used.
Regards,
Dr.S.Gunasakaran,MBBS,MD.,
Medical Affairs
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