# 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
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

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 - 16:05:58 EST

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