- On 18 Sep 2000 at 13:45:14, Maria Toledo (mitoledo.-at-.yahoo.com) sent the message

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Dear all

In a bioavailability assay, could I calculate the time

of performing the last sample collection so that I

obtained 80% of the AUC?

Thank you for replay.

Maria Ines de Toledo - On 19 Sep 2000 at 10:51:39, ml11439.-at-.goodnet.com sent the message

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Maria,

I think that the time of the last sample for which 80% of

the AUC would be included could be calculated after estimating

the Ke. The following calculations were performed for an IV bolus

in a one compartment model:

Fraction 0.8 = AUC(o->t)/AUC(o->inf)

= [(Co/Ke)(1-e-Ket)]/[Co/Ke]

= (1-e-Ket)

Time 0.8 = Ln(0.2)/(-Ke) = 1.60943791/(Ke)

Example: T1/2= 2 hours Ke= .693/2= .3465 hr-1

Time 0.8= 1.60943791/Ke= 4.6448425 hours

Mike Leibold, PharmD, RPh

ML11439.-a-.goodnet.com - On 21 Sep 2000 at 15:10:48, "David Nix, Pharm D." (nix.at.Pharmacy.Arizona.EDU) sent the message

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I assume that you are not modeling the PK for bioavailability. The best

option is to obtain some prior data on the product. The data can be

analysed via non-compartmental methods using only data for selected time

points. For example - choose all concentrations <= 8 hours and

determine AUC(0-t) and AUC(0-inf). If AUC(0-t)/AUC(0-inf) < 0.8 then

samples collected over 8 h would be acceptable. Repeat this process

with other selected times. However, I would urge you to use 90 or 95%

rather than 80% for the measured area relative to extrapolated area.

If you do have a drug that has been modeled, you can use fitted

parameters and the appropriate structural model to calculate the time to

80% of AUC or perform simulations.

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