# PharmPK Discussion - 3 Questions and 1 Suggestion

PharmPK Discussion List Archive Index page
• On 7 Jan 1997 at 10:59:41, "Tony Lee" (p2149z.at.www.hotmail.com) sent the message
`Hi there, I have two questions about PK modeling, one question aboutthe learning chance and one suggestion for this discussion group.Thank you very much in advance for the information you=EDll give.1.  I am doing simultaneous curve fitting for drug concentration-timedata in several tissues using compartmental models with PCNonlin.Since drug concentration magnitude is very different, say, one tissueconcentration is 700 mg/g and another is 0.5 mg/g. It was suggested totransform the data into dimensionless value to get the concentrations at thesame scale or even use the logarithmic transformation to decrease the datadistance. My questions are (1) is there any reference about such datatransformation in PK, (2) how to transform the data into the same magnitude and(3) if I transform the data by dividing them by their averages, which way Ishould go, transforming the data first and then doing the modeling or using theaverages as  weighting factors-but how to write the weighting command for theaverage weighting option.2.  Is there any "tricky" part about fitting infusion data from both infusionand postinfusion periods? I can use following differential equations tosimultaneously fit the data of both periods.If t>240, thendz(1)=-kel*z(1)elsedz(1)=D/(T*V)-kel*z(1)endifThe problem is I can fit the infusion period well but the results ofsimultaneous fit were not satisfying, specially the postinfusion period. Isthis problem model-related or drug disposition different between the infusionand postinfusion periods?3.  Is there any cheap way for a graduate student to learn how to use theprogram, Nonmem? Any online course about the PK programs?4.  I have found the discussions in this PK and PD group are very informative.But how about an idea that there is a monthly important PK/PD topic discussionbrought up by some experts besides the individual Q&A pattern.Tony Leemailto:p2149z.at.hotmail.com`
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• On 8 Jan 1997 at 14:09:41, Bob Phair (rphair.-a-.ix.netcom.com) sent the message
`Response to Tony Lee:Your problem concerning what you call a large "data distance" is verycommon inphysiological modeling because biological concentrations can range from1E-2 M down to1E-15 M or even less. A standard solution to this large dynamic rangeproblem involvesusing relative weighting instead of absolute weighting of the data to befitted. I'mnot familiar with the way PCNonlin handles this situation, but I'm quitecertain youcould solve this problem easily in SAAM II.I believe you could also reproduce your infusion-postinfusion protocolquite easily inSAAM II, and all without writing code or having to own a compiler.Last I knew, the SAAM Institute was still offering deep student discountson thepurchase of SAAM II. You can reach them at 1-800-421-SAAM orsaam.aaa.saam.washington.eduI've used the SAAM II software for several years, and have taught it tomore than 100undergraduate and graduate students. It is *very* easy to use.Good luck and let me know how you make out.Regards,Bob--Robert D Phair PhD: rphair.-at-.ix.netcom.comBioInformatics Services: http://www.webcom.com/rphairPartnering and Outsourcing for Computational Biology`
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