- On 26 Dec 2005 at 00:16:49, Wayne Luther (wayneluther.at.gmail.com) sent the message

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Hi all,

I've tried to search for the equations for calculating Tmax and Cmax

for first-order absorption in a 2-compartment model, however, the

only equations I found are:

Tmax = (ln(ka) - ln(k)) / (ka - k)

Cmax = (F * Xo * exp (-k * tmax)) / V

which are for 1-compartment model only.

Does anybody know the equations for 2-compartment model?

Thanks in advance,

Wayne - On 26 Dec 2005 at 15:03:34, "Nadeem Irfan Bukhari" (nadeemirfan_bukhari.aaa.imu.edu.my) sent the message

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The following message was posted to: PharmPK

Dear Wayne

The information I have for Tmax and Cmax is as:

Tmax for bioexpoential oral is

[2.303/lamda a-lamdaz] log [lamdaa/lamdaz]

Cmax for bieqponential oral is

FD exp[-lamdaz.tmax] / vd(area)

Nadeem Irfan Bukhari

Lecturer Pharmaceutical Technology,

International Medical University,

Bukit Jalil 57000, Kuala Lumpur, Malaysia

Web: http://www.imu.edum.my

Tel: +60 3 8656 7228, Ext. 1186; Fax: 86567229

C/P: +60 12 3242264 - On 26 Dec 2005 at 08:31:32, "Henri Merdjan" (henri.-at-.novexel.com) sent the message

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The following message was posted to: PharmPK

Dear Wayne,

You are right in saying that these equations only apply to a one-

compartment model.

No such algebraic equations exist for two-compartment models, or higher.

If you are interested in getting a model-predicted estimate of tmax

and Cmax, one possible option is to use an iterative approach.

Hope this will help.

Best regards,

Henri MERDJAN, Pharm, AIHP

Head of Drug Metabolism and Pharmacokinetics

NOVEXEL S.A.

Parc Biocitech

102 Route de Noisy

F-93230 Romainville

France

Tel +33 (0)1 57 14 07 45

Fax +33 (0)1 48 46 39 26

Web www.novexel.com - On 26 Dec 2005 at 08:31:32, "Henri Merdjan" (henri.-at-.novexel.com) sent the message

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The following message was posted to: PharmPK

Dear Wayne,

You are right in saying that these equations only apply to a one-

compartment model.

No such algebraic equations exist for two-compartment models, or higher.

If you are interested in getting a model-predicted estimate of tmax

and Cmax, one possible option is to use an iterative approach.

Hope this will help.

Best regards,

Henri MERDJAN, Pharm, AIHP

Head of Drug Metabolism and Pharmacokinetics

NOVEXEL S.A.

Parc Biocitech

102 Route de Noisy

F-93230 Romainville

France

Tel +33 (0)1 57 14 07 45

Fax +33 (0)1 48 46 39 26

Web www.novexel.com - On 26 Dec 2005 at 18:38:52, David Foster (david.foster.-at-.adelaide.edu.au) sent the message

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The following message was posted to: PharmPK

Hi Wayne,

Simple answer: you cant solve it with an algebraic equation...the

"easy way" is to solve for Tmax by integration (ie. find 't" where

'c' is maximised), then plug in tmax and get Cmax. I went through

this a few years ago, and that was the response. You can do this

easy enough in Excel using Solver...just write the PK equation and

the parameters, and use solver for each subject.

Hope this helps,

Dave

David Foster, PhD

NHMRC Research Officer

Department of Clinical and Experimental Pharmacology

Faculty of Health Sciences

The University of Adelaide

Adelaide, South Australia 5005

Tel: +61 08 8303 5985

Fax: +61 08 8224 0685

Email: david.foster.-at-.adelaide.edu.au

http://www.adelaide.edu.au/health/pharm/ - On 26 Dec 2005 at 16:47:51, "Kumaran Viswanathan" (kumarnpharm.aaa.medscape.com) sent the message

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The following message was posted to: PharmPK

Dear Mr. Wayne,

To get to know more about the equations and fundamentals of

Pharmacokinetics, pls refer the following book.

Pharmacokinetics by Milo Gibaldi and Gibaldi Gibaldi, 2nd edition

(revised), published by Marcel and Dekker, NY.

Kumaran Viswanathan - On 26 Dec 2005 at 11:11:14, "Brian M. Sadler" (bsadler1.-a-.nc.rr.com) sent the message

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The following message was posted to: PharmPK

Wayne,

For a two-compartment model, simply differentiate the bi-exponential

form

with respect to time and solve for dC/dt=0 (the inflection point at

tmax).

Then substitute tmax back into the bi-exponential equation to solve for

Cmax.

Cheers... Brian

Brain M. Sadler, Ph.D.

Strategic PK Consulting, LLC - On 26 Dec 2005 at 10:04:50, "David S. Farrrier" (DFarrier.aaa.SummitPK.com) sent the message

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Wayne,

A listing of equations for some 75 common pharmacokinetic parameters,

including Tmax and Cmax, is available free on our web site at

www.SummitPK.com (home of PK Solutions for easy pharmacokinetic

analysis). Follow either the link to the PK Equations page, or to the

Download page to obtain a copy.

Regards,

David S. Farrier, Ph.D.

Summit Research Services

DFarrier.-at-.SummitPK.com

www.SummitPK.com

970-249-1389

/\ /\

SummitPK.com /\ / \ /\ / \

/ / / /\ / \

David S. Farrier, Ph.D. Phone: 970-249-1389

Summit Research Services Fax:: 970-249-1360

68911 Open Field Dr. Email: DFarrier.aaa.SummitPK.com

Montrose, CO 81401 Web: http://www.SummitPK.com

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