NONMEM Users Network Archive

Hosted by Cognigen

RE: How to calculate t1/2, z?

From: Samtani, Mahesh [PRDUS] <MSamtani>
Date: Mon, 22 Feb 2010 16:05:58 -0500

Hello,

There is an Excel spread sheet convert.xls for doing this, developed by
Dr. Steven Shafer. Please see this NMusers posting to download the
spread sheet (Terminal half-life will be 0.693 divided by the slowest
lambda rate constant from the excel spread-sheet):
http://cognigencorp.com/nonmem/nm/97aug142001.html

 

Best wishes,

MNS

 

From: owner-nmusers
On Behalf Of Serge Guzy
Sent: Monday, February 22, 2010 3:20 PM
To: Li Y. Chen ; nmusers
Subject: RE: [NMusers] How to calculate t1/2, z?

 

Dear Li

I do not know if it will help you but here is a set of equations that
may be useful for you.

 

The initial parameterization I am using for the 3 compartment model with
first order absorption are different than yours but are sometimes
necessary to insure identifiability:

 

 

            CL,V2,V3,V4,Q3,DK42 and DKA

 

Then the series of equations 9already coded in Fortran) allow you to
estimate alpha, beta and gamma. I guess that the half-life you are
talking about would be Ln(2)/Gamma

 

 

      K10=CL/V2

       K23=Q3/V2

c to be consistent with the regular 3 compt model, we define

      k12=k23

 

      K32=Q3/V3

 

c to be consistent with the regular 3 compt model, we define

 

      k21=k32

 

      K42=K32+DK42

 

 

c to be consistent with the regular 3 compt model, we define

 

      k31=k42

 

 

       Q4=K42*V4

       K24=Q4/V2

       EX2=K23+K24+K10

       EX3=K32

       EX4=K42

       PX=EX2+EX3+EX4

       QX=EX2*EX3+EX2*EX4+EX3*EX4-K23*K32-K24*K42

       RX=EX2*EX3*EX4-K23*K32*EX4-K24*K42*EX3

       AX=(3D0*QX-PX*PX)/3D0

       BX=(2D0*PX*PX*PX-9D0*PX*QX+27D0*RX)/27D0

      

      TERM1=(-BX/2D0)/DSQRT(-AX*AX*AX/27D0)

C WE AVOID VALUES <-1 AND >1

            IF(TERM1.LT.-1.)THEN

            TERM1=-0.999

            ENDIF

 

            IF(TERM1.GT.1.)THEN

            TERM1=0.999

            ENDIF

 

            

 

c TX=DACOS( (-BX/2D0)/DSQRT(-AX*AX*AX/27D0) )

       TX=DACOS(TERM1)

       ALPH=PX/3D0-2D0*DSQRT(-AX/3D0)*DCOS(TX/3D0+2D0*PI/3D0)

       alpha=ALPH

       BETA=PX/3D0-2D0*DSQRT(-AX/3D0)*DCOS(TX/3D0+4D0*PI/3D0)

 

       GMMA=PX/3D0-2D0*DSQRT(-AX/3D0)*DCOS(TX/3D0)

       gamma=gmma

       KA=ALPH+DKA

 

C Terminal half-life

      Terminal_half_life=dlog(2)/gamma

 

 

Best Regards;

Serge Guzy;Ph.d

President, CEO; POP_PHARM

 

 

 

 

From: owner-nmusers
On Behalf Of Li Y. Chen
Sent: Monday, February 22, 2010 8:17 AM
To: nmusers
Subject: [NMusers] How to calculate t1/2, z?

 

I have a three-compartment model. Dose anyone know how to calculate the
terminal half life (t1/2, Z) using the finial estimates (V2, V3, V4,
CL2, CL3, and CL4)?

t1/2, z= ln2*Varea/CL, should Varea =V2+V3+V4? How about CL?

Thank you!

Li

 

________________________________

The information contained in this email message may contain confidential
or legally privileged information and is intended solely for the use of
the named recipient(s). No confidentiality or privilege is waived or
lost by any transmission error. If the reader of this message is not the
intended recipient, please immediately delete the e-mail and all copies
of it from your system, destroy any hard copies of it and notify the
sender either by telephone or return e-mail. Any direct or indirect use,
disclosure, distribution, printing, or copying of any part of this
message is prohibited. Any views expressed in this message are those of
the individual sender, except where the message states otherwise and the
sender is authorized to state them to be the views of XOMA.


Received on Mon Feb 22 2010 - 16:05:58 EST

The NONMEM Users Network is maintained by ICON plc. Requests to subscribe to the network should be sent to: nmusers-request@iconplc.com.

Once subscribed, you may contribute to the discussion by emailing: nmusers@globomaxnm.com.