Abstract
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Formulations containing nanosized drug particles such
as nanocrystals
and nanosized amorphous drug aggregates recently came into light as
promising strategies to improve the bioavailability of poorly soluble
drugs. However, the increased solubility due to the reduction in particle
size cannot adequately explain the enhanced bioavailability. In this
study, the mechanisms and extent of enhanced passive permeation by
drug particles were investigated using atazanavir, lopinavir, and
clotrimazole as model drugs. Franz diffusion cells with lipid-infused
membranes were utilized to evaluate transmembrane flux. The impact
of stirring rate, receiver buffer condition, and particle size was
investigated, and mass transport analyses were conducted to calculate
transmembrane flux. Flux enhancement by particles was found to be
dependent on particle size as well as the partitioning behavior of
the drug between the receiver solution and the membrane, which is
determined by both the drug and buffer used. A flux plateau was observed
at high particle concentrations above amorphous solubility, confirming
that mass transfer of amorphous drug particles from the aqueous solution
to the membrane occurs only through the molecularly dissolved drug.
Mass transport models were used to calculate flux enhancement by particles
for various drugs at different conditions. Good agreements were obtained
between experimental and predicted values. These results should contribute
to improved bioavailability prediction of nanosized drug particles
and better design of formulations containing colloidal drug particles.
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