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RE: How to calculate t1/2, z?

From: Serge Guzy <GUZY>
Date: Mon, 22 Feb 2010 12:19:42 -0800

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


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Received on Mon Feb 22 2010 - 15:19:42 EST

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