# RE: Weibull distribution

From: Steve Troy <stroy>
Date: Wed, 11 Apr 2007 10:02:03 -0400

Dear Abduljalil,

I am not an expert on using the Weibull distribution for drug
absorption, but I suspect that the value of TIME in the equation for
DADT(1) should represent the elapsed time since the most recent dose.
For example, if dosing occurs at 0, 24, and 48 hours, then the
observation at 25 hours after the start of the study (ie, 1 hour after
the most recent dose) should use TIME=1 hour in the equation for
DADT(1). However, I suspect that TIME=25 hours is being used in the
current problem.

Good luck,

Steve

-----Original Message-----
From: owner-nmusers
On Behalf Of Khaled Mohammed Abduljalil
Sent: Wednesday, April 11, 2007 9:15 AM
To: nmusers
Subject: [NMusers] Weibull distribution

Dear NONMEM users,

I have tried to study the pk profiles of a drug after
multiple oral dosage regimen of 500mg every 12hr. The
estimation process was well performed with the first dose
(only) using Weibull function. but if i apply the same
control file to the whole data (ie, single dose and
multiple doses), it does not work any more. I can not
detect my error. Could any one tell me where is it?
neither first order nor Mich.-Menten models fitted the
data like weibull model.

sincerely yours
Abduljalil

\$MODEL
COMP=(DEPOT,DEFDOSE)
COMP=(CENTRAL,DEFOBS)

\$PK
CL=THETA(1)*EXP(ETA(1))
V=THETA(2)*EXP(ETA(2))
BETA=THETA(3)*EXP(ETA(3))
ALPHA=THETA(4)*EXP(ETA(4))

K=CL/V

S1=1
S2=V

\$ERROR
DEL=0
IF(F.EQ.0) DEL=0.001
W=F
IPRED=F
IRES=DV-IPRED
IWRES=IRES/(W+DEL)
Y=F+EPS(1)

\$DES
B
ETA)

\$THETA
(0.01,17,80);
(10,115,900);
(0.1,2.2,30)
(0.1,2.6,30)
(0.001,2)
(0.001,1)

\$OMEGA
0.1 0.2 0.08 0.2

\$SIGMA
0.2

\$EST METHOD=1 INTER PRINT=5 NOABORT MAXEVAL=9999
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Received on Wed Apr 11 2007 - 10:02:03 EDT

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