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I concur with the sentiment expressed by Dyal Greg (E-mail on 5/17/96) and
put it this way: PK studies are basically an analytical pursuit. The use of
control samples in toxicology stuides or the use of placebos in efficacy
studies are, of course, legitimate and essential, because these studies use
biological responses as enpoints and the comparison with a "'no dose" level
is essential. On the other hand, since PK information depends only on
analytical data, the routine analysis of control samples and placebos
produces information which has no use other than to show that the drug was
absent.
Too often in PK/ADME studies the protocol includes the use of a control (no
dose) group of animals. I suggest that this is a carry over from toxicology
and is non-essential. The FDA/EPA regulations acknowledge the need for
control samples to be used primarily in method development (e.g., to
ascertain the absence of analtytical interferences or to determine
extraction efficiencies). But beyond that, I see no value in the routine
analysis of controls, placebo groups, or other no dose groups otherwise
included in the design for physio/pharmalogical or bio-comparative (but not
analytical) purposes.
The analysis of a pre-dose sample from each patient or animal seems
sufficient to answer the analytically pertinent questions regarding
potential interferences, contamination, etc. This is also more
cost-effective as well as pragmatic viewpoint.
David S. Farrier, Ph.D.
Summit Research Services
(PK/ADME consulting, study management, and software)
1374 Hillcrest Drive
Ashland, OH 44805
419-289-9207
E-mail: dfarrier.aaa.bright.net
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