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Estimation of Intake Time

From: Andrzej Bienczak <andrzej.bienczak>
Date: Thu, 18 Jun 2015 15:35:30 +0200

Dear NMusers,

 

I would like to present you with a problem that some of you might have faced
before. I am currently building a PK model for a drug with once daily oral
administration. The drug has a long half-life and can be taken either in the
morning or at night. Unfortunately due to lack of consistency in the
recording of the administration times by the study team part of the patients
flagged to have taken the medication in the mornings were in fact taking it
at night (i.e. 08:25 corresponds to 20:25 the previous day). At this stage
there is no way of tracking back what the correct intake times were.

 

The data consists of 2 sparse measurements per patient and indeed looking at
individual profiles you can clearly see that some samples are from the
elimination phase, indicating the drug was taken more than 12h prior. I
could correct the dataset based on an empirical judgement backed up by the
visual analysis but I was hoping there would be a more robust way.

 

Is there any way to put a THETA on the dosage time for those patients to let
NONMEM estimate a corrected administration time?

 

I tried simply adding an extra parameter on the intake time for those
patients (placed the code in $PK):

IF(FLAG_AM.EQ.1) TIME=TIME-THETA(17)

 

But received the following error message:

 

AN ERROR WAS FOUND IN THE CONTROL STATEMENTS.

 AN ERROR WAS FOUND ON LINE 30 AT THE APPROXIMATE POSITION NOTED:

    IF(FLAG_AM.EQ.1) TIME=TIME-THETA(17)

                     X

 THE CHARACTERS IN ERROR ARE: TIME

236 DATA ITEM MAY NOT BE CHANGED WITH THIS VALUE OF ICALL.

 

 

I would be grateful for some suggestions on how to deal with this issue.

 

Regards,

 

Andrzej

 

 

Andrzej Bienczak

MSc, MPharm, DiplPharm

Pharmacometrics Group

Division of Clinical Pharmacology

Department of Medicine

University of Cape Town

 

 


Received on Thu Jun 18 2015 - 09:35:30 EDT

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