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Hi all,
Does anyone have a formula which describes a steady-state
concentration-time profile from basic microconstants for a
2-compartment open model (ie. k10, k12, etc)? We need to simulate
concentrations at any time point after a steady-state dose. Is this
even possible (ie. something that can be computated within Excel, and
not with the use of a program, like ADAPT)?
Best regards,
Rob Ariano
Robert Ariano, Pharm.D.,BCPS
Clinical Pharmacist Critical Care
St.Boniface General Hospital; &
Associate Professor of Pharmacy,
& Medicine, University of Manitoba,
rariano.-at-.sbgh.mb.ca
www.sbgh.mb.ca
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[A few replies - db]
From: "David M. Foster"
Date: Thu, 4 Apr 2002 07:58:08 -0800
To: david.at.boomer.org
Subject: Re: PharmPK Formula for steady-state 2 compartment model
I think it may be possible with Excel, but programs such as ADAPT or SAAM II
(www.saam.com) do it quickly and easily.
David Foster, PhD, CEO
SAAM Institute, Inc.
---
From: "David S. Farrier"
Date: Thu, 04 Apr 2002 10:07:30 -0700
To: david.aaa.boomer.org
Subject: Re: PharmPK Formula for steady-state 2 compartment model
Rob,
Although our Excel-based PK Solutions pharmacokinetics analysis
program is designed primarily for easy computation of
noncompartmental pharmacokinetics, it does include the 2-comp
microconstants you mentioned above and will simulate and graph a
repeated dose regimen based on single dose data.
You are invited to download a list of equations and a demo to see if
this proves useful to your needs at www.SummitPK.com
Regards
David
David S. Farrier, Ph.D.
Summit Research Services
68911 Open Field Dr. Email: DFarrier.at.SummitPK.com
Montrose, CO 81401 Web: http://www.SummitPK.com
---
From: Spiresgate.at.aol.com
Date: Thu, 4 Apr 2002 12:18:17 EST
To: david.at.boomer.org
Subject: PharmPK Formula for steady-state 2 compartment model
Dear Rob
The question is a bit confusing; presumably at steady-state the concentration
is constant.
However assuming you mean how do you model the concentration-time profile for
multiple doses then this can be done relatively simply using a spreadsheet.
The way to do it is best demonstrated with a spreadsheet example but David
will not allow attachments; I can send an example directly to you if you
wish.
[Files like these can be placed on web or ftp sites for download and
a link included in the message - db]
The key to the multiple dose simulation is to add the dose at preset time
intervals to the dosing compartment. I usually do this by adding an 'if'
statement to the formula for the dosing compartment, the simplest example
being:
if(b2=60,100,0)
where b is the column containing the time value, and the dose is 100.
Hope this makes some sense,
Joe Chamberlain
[After a single IV bolus C = A*exp(-a*t) + B*exp(-b*t). After a
regimen of the same bolus dose given at a regular intervals, T, the
equation becomes C = A*[(1-exp(-n*a*T))/(1-exp(-a*T))]*exp(-a*t) +
B*[(1-exp(-n*b*T))/(1-exp(-b*T))]*exp(-b*t)
where n is the number of doses and t is the time since the last dose.
See http://www.boomer.org/c/p1/Ch14/Ch1407.html for the one
compartment example
If the doses or intervals are not the same then you need to calculate
for each dose separately and add them together
(http://www.boomer.org/c/p1/Ch15/Ch1504.html).- db]
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