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Dear all,
I am very much thankful if some one explain or clarify about the
following query
Can we include the values in 0 hour (predose sample - before dosing of
drug) blood sample during PK analysis
Thanks
Sujatha
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The following message was posted to: PharmPK
Make sure you take a blood sample prior to dosing each animal. This
allows for a kind of internal control when dealing with an assay. If
the drug is novel you want to make sure there is no detection of your
compound in the system prior to dosing.
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Dear Sujatha,
Naturally values at time zero can be included in modeling and
analysis, see for example the study: DURISOVA, M., DEDIK, L.:
Comparative study of human pentacaine pharmacokinetics in time
and frequency domain. Methods and Findings in Experimental and
Clinical Parmacology 16, 1994, 219-232.
With best regards,
M.Durisova DSc (Math/Phys)
http://www.uef.sav.sk/advanced.htm
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Dear Sujatha, We have to include 0 hour values for PK analysis which
will be useful during calculating AUC 0 - max and AUC 0 -infinity.
D.Singh
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Dear Sujatha:
Since there should not be any drug in the blood/plasma at zero hour
following administration of single dose, it would appear that one can
use the zero hour velue as zero in PK analysis after single dose.
Following multiple doses, depending on the dosing interval and half
life of the drug, the predose blood/plasma sample (Cmin or trough
values) may or may not be zero and in this case one should not use the
predose sample as zero for PK calculations.
I hope this helps. It would be interesting to hear views from other PK
scientists.
Aziz Karim
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Dear Sujatha
Indeed as Aziz wrote: Since there should not be any drug in the blood/
plasma at zero hour
following administration of a single dose, one can use the zero hour
value as zero in PK analysis after single dose.
This is true for most administration routes.
However, when you have given an IV Bolus injection and use the IV
bolus model that extrapolates back (using C1 and C2 at time t1 and t2
post-dose) to estimate C0, then you would not use a concentration 0 at
t=0. This model assumes instant distribution of the dose in the
central compartment and calculates the hypothetical concentration at
time 0.
In my experience it works better though to use a model for IV infusion
and to set the infusion time to the time needed for the bolus
injection and then you would use concentration 0 at time 0. That way
you can avoid estimations of C0 by back extrapolation (which may not
be very reliable) and the Cmax is then usually the concentration in
the first sample post-dose. This model also works well if you have pre-
dose values that are not 0 in a multiple dose study.
Kind regards
Frieda
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