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greeting everyone,
i know my question might be too easy but it seems quite difficult for
me to understand because i'm just a new beginer in this field of
study. so i want to ask why we can not add AUC t-infinity (t last
sampling) if the value of AUC t-infinity is more than 10% (90% dose
excreted) in order to get AUC 0-infinity?
KR,
Nisak
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Hi, Nisak
While we do the PK study, the time for sampling should as long as to
describe the in vivo process of the determined drug completely.
Commonly, three half-life period is considered reasonable. That means,
the drug concentration should be less than 12.5 % to the Cmax
(C=Cmax*(1/2)^3=0.125Cmax) . Therefore, there will be no significant
difference between the AUC(0-t) and AUC(0-inifity) thus we can add the
AUC(t-inifity) to AUC(0-t) and get the AUC(0-inifity).
For any other information, you can referent some professional books
about the pharmacokinetics.
Hope this can give you any help !
--
Best Regards,
Alec H Yu
Department of Biochemistry,
Hong Kong University of Science & Technology, HKUST
Clear Water Bay
Kowloon, Hong Kong
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The following message was posted to: PharmPK
Dear Nisak,
You wrote:
> so i want to ask why we can not add AUC t-infinity (t last
sampling) if
> the value of AUC t-infinity is more than 10% (90% dose excreted)
in order
> to get AUC 0-infinity?
There are (at least) two reasons:
- the estimate of AUC(0-infinity) is less precise if the extrapolated
part
is too large; of course the 10% (or 20%) extrapolation is an arbitrary
bound, but the extrapolated AUC is very sensitive to relatively small
changes in the last observations;
- the estimate of AUC(0-infinity) may be inaccurate if the terminal
half-life has not yet been reached, i.e. if the estimated terminal
half-life
is affected by absorption or distribution; this would lead to
overestimation
or underestimation of the AUC, respectively.
best regards,
Hans Proost
Johannes H. Proost
Dept. of Pharmacokinetics, Toxicology and Targeting
University Centre for Pharmacy
Antonius Deusinglaan 1
9713 AV Groningen, The Netherlands
Email: j.h.proost.aaa.rug.nl
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