RE: How to calculate t1/2, z?
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
Quoted reply history
From: [email protected] [mailto:[email protected]]
On Behalf Of Serge Guzy
Sent: Monday, February 22, 2010 3:20 PM
To: Li Y. Chen ; [email protected]
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: [email protected] [mailto:[email protected]]
On Behalf Of Li Y. Chen
Sent: Monday, February 22, 2010 8:17 AM
To: [email protected]
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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