RE: Coding a triple absorption model

Date: Thu, 4 Jun 2009 17:58:53 -0400

Hello Mahesh,

The use of a sum of inverse Gaussian functions to describe the =
absorption profile of drugs exhibiting complex absorption.Csajka C, =
Drover D, Verotta D.
Pharm Res. 2005 Aug;22(8):1227-35. Epub 2005 Aug 3.

It details how to constraint F's when you have multiple absorption =
components as in your case. It includes two different methods for =
parametrization(P1) and (P2) as well as useful equations that can be =
coded into nonmem easily.

Hope this helps,

Samer

-----Original Message-----
From: owner-nmusers
Sent: Thu 6/4/2009 16:34
To: nmusers
Subject: [NMusers] Coding a triple absorption model

> Dear NMusers,
I am using a dual absorption model as follows (The dose is split into 2 =
fractions and the splitting fraction, THETA(.), is an estimated =
parameter in the model):

TPH = LOG(THETA(.)/(1-THETA(.)))
TH = EXP(TPH+ETA(.))/(1+EXP(TPH+ETA(.)))
F2 = TH
F1 = 1-TH

However, upon prolonged sampling we can observe a 3rd shallow phase. I =
would like to use a 3-depot absorption process with F1, F2 and =
F3=1-F1-F2. Both F1 and F2 need etas using some type of transformation =
such that neither one of them exceed 1 nor does their sum exceed 1. Can =
some one kindly provide the NONMEM code.