Recent research on nanocomposites as potential
pharmaceutical carriers, is focused on utilization of
inorganic matrices with layered structure in which
bioactive molecules/drugs are incorporated. One of
the promising inorganic material with such layered
structure is clay, which is quite common ingredient
in pharmaceutical products, both as excipient or
active substance. Clay minerals are not only “inert
ingredients”, but they can also be used to decrease
or increase dissolution rate, delay and/or target drug
release, to prevent possible side effects, taste masking
or increase stability. Prosperity of clay-based drug
delivery systems depends on the amount of a drug
retained by the clay, on its release kinetics and on
the total amount released during therapeutic regime.
Thus, it is very essential to understand and to improve
the physico–chemical aspects of drug–clay complexes.
The aim of this research is to provide more information
on drug-clay stability formulations.
Pyrophyllite clay, (Parsovići, Konjic, Bosnia and
Herzegovina), Al2
Si4
O10(OH)2
, is a smectite clay type
(talc-pyrophyllite group) and was used here as a
potential pharmaceutical carrier. Stability of pyrophillite
and bioactive molecule/drug was estimated by use of
thermal analysis methods (differential thermal analysis/
thermogravimetric analysis – TGA/DTA) and Fouriertransform infrared spectroscopy (FTIR). Additionally
detailed kinetic study was done using contemporary
kinetic software in order to evaluate kinetics of clay/
bioactive molecule (drug) complex. Antimicrobial
study was performed against Staphylococcus aureus
(Gram positive bacteria) and Escherichia coli (Gram
negative bacteria) using batch experimental method.
In epruvetes with 9.9 mL of Muller- Hinton broth and
0.1 mL of bacterial inoculum adjusted to 0.5 McFarland
standard was added 1 gram of sterilized pyrophillite.
Incubation with 120 rpm shaking was performed
during 24h at 37 0
C.
Decomposition of neat pyrophillite is one-step process
with following kinetic triplet: Ea (activation energy) –
216 kJ/mol; A (pre-exponential factor) – 4.1687 x 1010
s-1 and N-th order model, while clay/drug mixture
decomposition is a four step process. Third stage in
mixture decomposition is of special interest, because
decomposition of pyrophillite is happening there.
Kinetic parameters for the third stage are as follows: Ea –
176 kJ/mol, A – 6.537 x 108
s-1 and the N-th order model
also gave the best fit. After overnight incubation, we
noticed highly significant removing of both bacteria
from broth. Staphylococcus aureus was reduced from
2.3 x 109
cfu/mL to 5.5 x 106
cfu/mL, while Escherichia
coli was reduced from 4.5 x 1011 cfu/mL to 3.5 x 108
cfu/
mL.
Based on the kinetic results we can conclude that
thermal stability of pyrophillite is slightly lowered
comparing to neat pyrophillite data, but on the
other hand pyrophillite did not make any impact on
thermal stability of other components in mixture. This
information is of great interest for stability assessment
of clay/drug mixture.
