NONMEM Users Network Archive

Hosted by Cognigen

RE: PK data from individuals who vomited after drug ingestion

From: Seng Kok Yong <skokyong>
Date: Thu, 27 Aug 2009 13:52:32 +0800

Dear Nick,

Thank you for your reply. Yes, a single compartment model with
Michaelis-Menten elimination fits the data significantly better compared
to a single compartment model with linear elimination.

GAM analysis, using AIC, and covariate analysis within NONMEM do not
suggest that vomiting incidence is a significant covariate. Could this
be attributed to the fact that the systemic alcohol levels at the time
of vomiting (~1 h post-dose) is only about 25% of what they consumed
(assuming a elimination half-life of 30 min)? Or, could it be because
the number of vomiting cases makes up only 15% of the total number of

Thank you and best wishes,
Kok-Yong Seng

-----Original Message-----
From: owner-nmusers
On Behalf Of Nick Holford
Sent: Thursday, 27 August 2009 1:15 PM
To: nmusers
Subject: Re: [NMusers] PK data from individuals who vomited after drug


I would not use a mixture model because you already have the information

about which group vomited.

I am surprised you describe the elimination of ethanol with a half-life.

If you gave an ethanol dose big enough to induce vomiting I would expect

you to describe elimination with a mixed order (saturable) elimination

Best wishes,


Seng Kok Yong wrote:
> Dear NM-users,
> I have a question regarding NONMEM modeling of PK data from
> individuals who vomited after drug ingestion. Basically, I have a set
> of data from about 150 subjects (about 5 measurements per subject) who

> orally ingested alcohol at time = 0 h. However, about 15% of this
> group vomited more than 1 h post-dose. Based on NONMEM modeling of PK
> data from subjects who did not vomit during the study, the mean
> elimination half-life is about 30 min.
> May I ask if I should model vomiting incidence (a "yes" or a "no") as
> a categorical covariate for analysis of all the data? I have
> demographic covariate information at hand. Or, should I introduce a
> mixture model during NONMEM modeling? I would expect the vomiting
> subgroup to display different values for Vd, Ka etc as compared to the

> non-vomiting subgroup.
> Thank you very much for your time and kind advice.
> Best wishes,
> Kok-Yong Seng, PhD
> DSO National Laboratories
> Republic of Singapore

Nick Holford, Professor Clinical Pharmacology
Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New
mobile: +64 21 46 23 53
Received on Thu Aug 27 2009 - 01:52:32 EDT

The NONMEM Users Network is maintained by ICON plc. Requests to subscribe to the network should be sent to:

Once subscribed, you may contribute to the discussion by emailing: