# PharmPK Discussion - BA calculations using SAS

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• On 25 Aug 2009 at 21:48:25, divakar chanti (dvkr82.-at-.gmail.com) sent the message
`I am fresher with graduation. I have doubts in sas how to calculateCmax, Auct,Aucinf, Tmax,Rsequare, Rseq-adjust,Correlation, Lambada_Z,Lambada_Z_lower, Lambada_Z_Higher using SAS.Please give me suggestions for how to write SAS Pogramming for BA-BEPlasma concentration data for all these parameters.Thanking you,with regards,aditya.`
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• On 26 Aug 2009 at 13:00:30, "V.G.S.Raghavendra Mamidi" (mamidi.ganesh.aaa.gmail.com) sent the message
`Dear Aditya,The following link may helps you in this:http://www.lexjansen.com/pharmasug/2005/statisticspharmacokinetics/sp07.pdfThis paper explains about the Noncompartmental analysis.Note: As you are a fresher you have to learn the knowledge how tocalculate these by manually. They you can go ahead in this field.Thank you,Regards,M.V.G.S.RaghavendraBiostatistician`
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• On 26 Aug 2009 at 10:10:46, "Hartstra, Jan" (HartstraJan.aaa.PRAIntl.com) sent the message
`The following message was posted to: PharmPKDear Aditya,For BA studies PK parameters are usually estimated usingNon-Compartmental Analysis (NCA).Calculating Cmax is simple: for instance by use PROC MEANS orequivalent,but PROC SQL can also be very useful:PROC SQL;   SELECT subject   ,      period   ,      time AS tmax   ,      conc AS Cmax   FROM ctdata   GROUP BY subject, period   HAVING conc=MAX(conc)   ;QUIT;(tmax is the time corresponding to Cmax, but be aware of multipleoccurances of Cmax.)AUC can be calculated by using the linear or log-linear trapezoidalrule.This requires DATA step programming.Good starting points for this can found in:http://www2.sas.com/proceedings/sugi27/p229-27.pdforhttp://www.lexjansen.com/pharmasug/2005/statisticspharmacokinetics/sp07.pdfLambda_z_lower and Lambda_z_higher should either be chosen1) by hand after inspection of a semi-logarithmic plot of theConcentration-time data   (you can use PROC GPLOT for this), or2) algorithmically (e.g. using an algorithm that maximizes Rsquare).Lambda_z can be calculated using PROC REG after log-transformation ofthe concentration datain the range [Lambda_z_lower, Lambda_z_higher].This PROC will then also provide you with Rsquare, Rsquare adjusted etc.AUCinf is then calculated by extrapolation using:AUCinf=AUClast + Clast/Lambda_zwhere Clast is either the observed concentration at t_last or theestimated concentrationfor t_last, using the regression equation provided by PROC REG whileestimating Lambda_z.(t_last is time-point of the last quantifiable concentration).Kind regards,JanJan Hartstra | Sr. Biostatistician | Early Development Services | PRAInternational`
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• On 26 Aug 2009 at 10:26:55, Walt Woltosz (walt.aaa.simulations-plus.com) sent the message
`The following message was posted to: PharmPKAditya,In my opinion, noncompartmental analysis is a crude way to calculateBA, butcan be useful. A particular caution is due to sampling times andcalculationof AUC. People often use a simple trapezoidal rule to integrate AUC oneither an absolute or log scale, and then take the highest observedconcentration as Cmax and the time of that observation as Tmax. But howlikely is it that a sample was taken exactly at the time Cmax occurred?I prefer to fit a good pharmacokinetic model (using GastroPlus(tm), butother tools are available), which can (and usually will) provide CmaxandTmax between observations. Cmax can be significantly higher than thehighestobservation in some cases. Of course, you need to be careful about amodelthat fits the data points well but is not realistic for various reasons.Walt WoltoszChairman & CEOSimulations Plus, Inc. (NASDAQ: SLP)42505 10th Street WestLancaster, CA  93534-7059U.S.A.http://www.simulations-plus.comPhone: (661) 723-7723FAX:   (661) 723-5524E-mail: walt.aaa.simulations-plus.com`
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