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Dear All,
A current study has finish the analytical procedures and test
substance has been found above lower limit of quantification in
seven volunteers ( first and second period) in baseline sample.
In an attempt to find out the fault some aspects have been reviewed.
The MS method validation had been used in a early study.
The analytical analyses have been redone six times every sample,
( two of them blind ).
Sending procedures and labeling and preparation of extracted samples
has being checked.
The values found present a curve with no problems beside this "small
one".
The test substance half life is short, so its the volunteers could
not have residual substance from other studies.
Please let me know if there is a checklist available for such
situation or if there are any crucial point I am missing.
Thanks in advance,
best regards,
Andre.
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Dear All,
A current study has finish the analytical procedures and test
substance has been found above lower limit of quantification in
seven volunteers ( first and second period) in baseline sample.
In an attempt to find out the fault some aspects have been reviewed.
The MS method validation had been used in a early study.
The analytical analyses have been redone six times every sample,
( two of them blind ).
Sending procedures and labeling and preparation of extracted samples
has being checked.
The values found present a curve with no problems beside this "small
one".
The test substance half life is short, so its the volunteers could
not have residual substance from other studies.
Please let me know if there is a checklist available for such
situation or if there are any crucial point I am missing.
Thanks in advance,
best regards,
Andre.
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The following message was posted to: PharmPK
Dear Andre,
Many analytical reasons can be the cause of the presence of a peak in a
predose or a blank sample :
1. Did you check the carry-over in you analytical run ? If you have a
too high carry-over and if your predose sample follows a highly
concentrated sample you can still find a peak in your predose sample
2. Are you sure that your solutions used for the processing of the
sample are not contaminated (eg. Internal standard working solution)? Do
your blank samples and blank samples spiked with IS also shows a peak at
the retention time of analyte?
3. During your validation did perform a matrix effect and selectivity
test ? Are your volunteers taking concomitant drugs, if yes did you
perform a selectivity test in presence of these drugs?
If you are sure that these points are ok, then probably your analytical
method is not the cause of this problem.
Hope this will help you.
Best regards.
Sebastien
Dr. Sebastien Block
Manager Bioanalysis
SGS India Pvt. Ltd.
Life Science Services
Ticel Biopark Ltd
Chennai, 600113, INDIA
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The following message was posted to: PharmPK
Dear Andre,
You did not mention the drug you are talking about. You can find some
pre-dose concentrations in period II, if your drug is metabolised by a
particular cytochrome P450 (CYP) and that particular subject is a slow
metaboliser for that drug.
Other possibility from the analytical point of view could be that there
can be some carry-over seen in your HPLC.
Regards
Dr. Tausif Ahmed
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Dear Andre,
Both previous answer are appropriate for your problem (i.e. residual
drug in period two probably because the wash out period was
sufficient) and the analytical issue.
In order to minimize the need of reanalysis, we have decided to
analyze the pre-dose samples with and without the presence of the
internal standard.
This serves two purposes, firstly it will demonstrate if the peak
observed in the pre-dose sample is a contamination or an actual peak
and secondly, with the IS present, you will be able to quantify it
and determine if it represents more than 20% of your LOQ.
Once the pre-dose sample concentration has been confirmed, it can be
taken into account when calculating AUC.
Finally, you can also introduce the analysis of a reagent blank (i.e.
biological matrix is replace by water) to eliminate the possible
contamination route.
Regards,
Sylvain Mandeville, Ph.D.
LAB research Inc.
www.labinc.hu
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The following message was posted to: PharmPK
Dear Sylvain,
you wrote:
>
>Once the pre-dose sample concentration has been confirmed, it can be
>taken into account when calculating AUC.
>
What /exactly/ would you suggest in such a case?
<>
best regards,
Helmut
--
Helmut Schuetz
BEBAC
Consultancy Services for Bioequivalence and Bioavailability Studies
Neubaugasse 36/11
1070 Vienna/Austria
tel/fax +43 1 2311746
Web http://BEBAC.at
BE/BA Forum http://forum.bebac.at
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Hello Helmut,
If you confirmed that there is a peak in the pre-dose samples, it
demonstrate that it is not an analytical error.
Then, this value can be used to normalize the AUC calculation.
We have observed, in the case of repeated daily exposure in animals,
that the pre-dose samples were not always free of analyte. We decided
to extract them with the IS in order to prevent repeated analysis of
a positive pre-dose.
Since then, we have modified our SOP to include the analysis of pre-
dose samples with and without internal standard and reduced the
number of repeat analysis drastically.
Regards,
Sylvain
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