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The kinetics of sorption of solutes by plastic intravenous delivery systems


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Kowaluk, Elzbieta Amelia 1984 , 'The kinetics of sorption of solutes by plastic intravenous delivery systems', PhD thesis, University of Tasmania.

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The kinetics of the sorption of a number of solutes by the
plastics of intravenous delivery systems were investigated.
Models based on diffusion theory and compartmental analysis
were developed and examined for .their ability to describe
the uptake of a number of solutes from aqueous solutions
stored in contact with the plastics. In deriving diffusion
equations it has been assumed, firstly, that diffusion of
solute in the plastic matrix is the rate-limiting step in
the sorption process (matrix-controlled sorption) and,
secondly, that both the plastic matrix and an interfacial
resistance barrier contribute to the diffusional resistance
encountered by the solute molecule (intermediate diffusion
kinetics). The situation in which diffusion across the
interfacial resistance barrier is the rate-limiting step
was also considered.
The ability of the diffusion and compartment models to
describe and predict the sorption of the nonelectrolytes,
nitroglycerin and diazepam, was examined. The diffusion
model seemed to be the more satisfactory model in respect
of both description and prediction of the drug uptake. The
compartment model appeared to describe the drug uptake at
earlier times, but was not able to describe the loss as
equilibrium was approached; nor could that model be
employed as a predictive method. The complete time-course,
including equilibrium, of the sorption of nitroglycerin and
diazepam was well-described by the (matrix-control) diffusion model. The diffusion model was also found to
predict accurately the rate and extent of nitroglycerin and
diazepam loss from solutions stored in plastic infusion
bags of different sizes and containing various volumes of
The sorption of several weak electrolytes, specifically pnitrophenol,
p-toluidine, warfarin sodium and
trifluoperazine dihydrochloride, during storage of
solutions of various pH in plastic infusion bags was also
studied. The rate and extent of sorption varied with pH in
a manner suggesting preferential uptake of the unionised
species. It was assumed that only the unionised species
was sorbed by the plastic matrix and the diffusion model
was modified accordingly. The uptake of p-nitrophenol and
p-toluidine was adequately described by the matrix-control
diffusion model, confirming quantitatively the relationship
between solute uptake and fraction unionised. However, the
uptake of warfarin sodium and trifluoperazine
dihydrochloride was significantly better described by the
intermediate diffusion model. It appeared that the rate of
uptake of the unionised form of these solutes was
diminished due to the influence of interfacial or aqueous
diffusional barriers. Solute lipophilicity, degree of
ionisation and diffusion coefficient appeared to be
important factors determining the relative contribution of
the interfacial barrier and the plastic matrix to the
overall diffusional resistance. Several approximations of the diffusion equations were
considered. These approximations suggested that the rate
and extent of solute uptake by the plastics of delivery
systems at early times can be described by a single
parameter. In general these approximations yielded
parameter estimates consistent with those obtained by
nonlinear regression using the full equations. A method of
discriminating between matrix-controlled and intermediate
sorption kinetics, based on these approximations, is also
The kinetics of solute loss from solution to plastic
tubings during the course of an infusion was also
investigated. The kinetics of loss could be interpreted in
terms of diffusion-controlled sorption of the unionised
solute by the plastic. Equations are presented to describe
the availability of diazepam, and possibly other solutes,
during infusion.
The interaction of chlormethiazole edisylate with the
plastic infusion systems displayed some unique
characteristics, and these were further examined. It was
found that, in some circumstances, chlormethiazole
edisylate was not only sorbed by the plastic, but also
permeated to the external environment. Furthermore,
plasticisation of the polyvinyl chloride by chlormethiazole
edisylate was observed. Some initial attempts at correlating the physicochemical
characteristics of a range of solutes with their plastic
sorption behaviour are also presented.

Item Type: Thesis - PhD
Authors/Creators:Kowaluk, Elzbieta Amelia
Keywords: Drugs, Intravenous therapy, Plastics in medicine, Diffusion
Copyright Holders: The Author
Copyright Information:

Copyright 1984 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, Hobart, 1985. Bibliography: leaves 192-225

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