Back to the Top
We are interested in the plasma or blood binding of propofol in the
rat. We try to measure the binding by equilibrium dialysis.
We
had some problems of adsorption of propofol to glass and plastics.
When collecting and storing the buffer from the dialysis cells in
eppendorf tubes, there is an almost 50% decrease of the concentration
in the buffer over a 2 hours period (concentration is about 100
ng/ml). Even when collecting and storing the buffer from the ED cells
in glass injection vials for the HPLC, propofol adsorps for 20 to 30%
after 2 hours. With blood or plasma , the adsorption to the
collecting tubes is negligible due to the high protein binding .
We have at this moment no evidence of adsorption of propofol to the
dialysis cells or membrane. According to different publications there
should be no problem!? There is evidence from the literature that
propofol adsorps to plastic materials used in infusion sets.
How should we overcome this problem of adsorption to glass or plastic
materials?
F. Belpaire and P. De Paepe
**********************************
Prof. Dr. F. Belpaire
Heymans Institute of Pharmacology
University of Gent Medical School
De Pintelaan 185
9000 Gent
Belgium
tel: 32/9/2403355
fax: 32/9/2404988
frans.belpaire.at.rug.ac.be
**********************************
Back to the Top
[Two replies - db]
Date: Wed, 28 Jul 1999 04:31:01 -0400
From: "Edward F. O'Connor"
Reply-To: efoconnor.-at-.snet.net
Organization: conn chem
X-Accept-Language: en
To: PharmPK.aaa.boomer.org
Subject: Re: PharmPK Propofol protein binding
Silanizing the glassware may help. I believe National scientific Co.
offers silanized glass and plastic tubes. There are also teflon coated
glass and pastic lab supplies available but these are expensvie. While
precoating your labware with a profolol analog might alos help it could
confound your assay even more.. The silanized materials may be the best
bet.
---
X-Sender: mazoit.-at-.MAILHOST.POP.u-psud.fr
Date: Wed, 28 Jul 1999 12:00:37 +0200
To: PharmPK.at.boomer.org
From: "Jean-Xavier.Mazoit.-a-.kb.u-psud.fr"
Subject: Propofol protein binding
Dear Dr Belpaire,
We had similar problems when trying to measure propofol binding to human
blood components. Binding to ultrafiltration membranes was important. At
high concentrations, binding may be important, therefore, we used a
co-binding technique with charcoal and/or erythrocytes followed by fitting
with implicit solution. The reference is Mazoit JX, Samii K. Binding of
propofol to blood components: Implications for pharmacokinetics and for
pharmacodynamics. Br J Clin Pharmacol 1999; 47: 35-42. On another hand,
we had no adsorption on glass nor on polypropylene tubes, when we did the
extraction rapidly. I think that polypropylene tubes are OK. Another
solution is to use glass tubes with silicone such as Prosil (try Vacutainer
tubes !). For HPLC, we used manual injection without problem. The
adsoprtion process is relatively slow and it is possible to overcome the
problem by these different techniques.
Good luck in your search for solutions.
Regards,
Jean Xavier Mazoit MD, PhD
Laboratoire d'Anesth=E9sie
Universit=E9 Paris-Sud
Facult=E9 de M=E9decine du Kremlin-Bic=EAtre
F-94276 Bic=EAtre France
Tel. (33) (0)1 49 59 67 35-37
(33) (0)1 45 21 34 41 (Hopital)
Fax (33) (0)1 45 21 28 75
e-mail Jean-Xavier.Mazoit.aaa.kb.u-psud.fr
Back to the Top
Frans Belpaire mentions the problem of propofol adherence to plastic
containers when performing equilibrium dialysis for determining the protein
binding of the drug. The problem, we think, is mostly with the long
residence times of the ligand in the vials for this type of analysis. In
our lab, when doing determining protein binding we always use MPS
ultrafiltration. With this method the ultrafiltrate is obtained in 5
minutes, so there is no danger of binding to the containers. It is applied
immediately after extracting the sample from each rat, or human, and the
ultrafiltrate is injected directly to the HPLC apparatus. The sample is
never kept in tubes or frozen. Once extracted and evaporated the solid
residue can be frozen in glass tubes without binding. Rosario Calvo Duo,
PhD
*************************************************************************
Department of pharmacology
Faculty of Medicine
University of the Basque
Leioa, Vizcaya 48940
Spain
tel: +34 946012761 UTC+1hour
fax: +34 944800128
*************************************************************************
PharmPK Discussion List Archive Index page
Copyright 1995-2010 David W. A. Bourne (david@boomer.org)