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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
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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
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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
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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
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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/
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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
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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
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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
/\ /\
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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
PharmPK Discussion List Archive Index page
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