paclitaxel and doxorubicin, to albumin or gelatin nanoparticles significantly enhanced
the efficacy against experimental tumours or human tumours transplanted into nude
mice in comparison to free drug. Similarly, drug release and polymer biodegradation
significantly influence the possibility of obtaining a fruitful nanoparticle system. The
factors generally responsible are solubility of drug; desorption of the surface bound or
adsorbed drug; drug diffusion through the nanoparticle matrix; nanoparticle matrix
erosion or degradation; and combination of erosion and diffusion processes. Accordingly, the solubility, diffusion and biodegradation of the matrix materials control the
release practice. When the dispersal of the drug is quicker than matrix erosion, the
mechanism of discharge is principally controlled by a diffusion process. When there
is a rapid initial release or “burst” it is chiefly accredited to inadequate binding of drug
to the large surface of nanoparticles. However, when the drug is loaded by the
incorporation method, there is a comparatively slight burst effect and persistent
release features. Similarly, when the particle is coated with polymer, the release is
then measured by dispersal of the drug from the core across the polymeric membrane.
6.1 Chitosan and Its Derivatives for Pharmaceutical Applications
Recently, the use of chitosan in drug formulation development has increased many
fold. Chitosan exhibits excellent compatibility with organic compounds such as
cationic dyes and surfactants, starches, quaternary ammonium salts and with most
cationic and non-ionic polymers. Multivalent anions can easily crosslink with
chitosan to form complexes. Chitosan has many advantages, including its cationic
nature that allows for ionic crosslinking with multivalent anions; its mucoadhesive
character, which increases residual time at the site of absorption; the lack of need to
use hazardous organic solvents for fabricating particles since it is soluble is aqueous
acidic solution; it is linear polyamine containing a number of free amine groups that
are readily available for crosslinking; and last but not least, its ability to control the
release of active agents. Chitosan has been investigated for its possible role in
controlling the release of active medicines.
To further enhance the solubility of chitosan and to improve its mucoadhesive and/or permeation enhancing properties, various derivatives such as
trimethylated chitosan [72], mono-N-carboxymethylchitosan, N-sulfo-chitosan
and chitosan–EDTA conjugates have been prepared. A further modification is
based on the immobilization of thiol-bearing moieties on the polymeric backbone
of chitosan.
6.1.1 Chitosan as Binder in Tablets
Chitosan (molecular weight, 19–400 kDa; degree of deacetylation, 75–98%) has
been evaluated as a directly compressible vehicle for tablets, but has found limited
utility due to the lack of good flow properties and compressibility. The influence of
excipient (lactose, sodium lauryl sulfate, sodium alginate, hydroxypropyl methyl
286
A.K. Anal and A. Tuladhar
the efficacy against experimental tumours or human tumours transplanted into nude
mice in comparison to free drug. Similarly, drug release and polymer biodegradation
significantly influence the possibility of obtaining a fruitful nanoparticle system. The
factors generally responsible are solubility of drug; desorption of the surface bound or
adsorbed drug; drug diffusion through the nanoparticle matrix; nanoparticle matrix
erosion or degradation; and combination of erosion and diffusion processes. Accordingly, the solubility, diffusion and biodegradation of the matrix materials control the
release practice. When the dispersal of the drug is quicker than matrix erosion, the
mechanism of discharge is principally controlled by a diffusion process. When there
is a rapid initial release or “burst” it is chiefly accredited to inadequate binding of drug
to the large surface of nanoparticles. However, when the drug is loaded by the
incorporation method, there is a comparatively slight burst effect and persistent
release features. Similarly, when the particle is coated with polymer, the release is
then measured by dispersal of the drug from the core across the polymeric membrane.
6.1 Chitosan and Its Derivatives for Pharmaceutical Applications
Recently, the use of chitosan in drug formulation development has increased many
fold. Chitosan exhibits excellent compatibility with organic compounds such as
cationic dyes and surfactants, starches, quaternary ammonium salts and with most
cationic and non-ionic polymers. Multivalent anions can easily crosslink with
chitosan to form complexes. Chitosan has many advantages, including its cationic
nature that allows for ionic crosslinking with multivalent anions; its mucoadhesive
character, which increases residual time at the site of absorption; the lack of need to
use hazardous organic solvents for fabricating particles since it is soluble is aqueous
acidic solution; it is linear polyamine containing a number of free amine groups that
are readily available for crosslinking; and last but not least, its ability to control the
release of active agents. Chitosan has been investigated for its possible role in
controlling the release of active medicines.
To further enhance the solubility of chitosan and to improve its mucoadhesive and/or permeation enhancing properties, various derivatives such as
trimethylated chitosan [72], mono-N-carboxymethylchitosan, N-sulfo-chitosan
and chitosan–EDTA conjugates have been prepared. A further modification is
based on the immobilization of thiol-bearing moieties on the polymeric backbone
of chitosan.
6.1.1 Chitosan as Binder in Tablets
Chitosan (molecular weight, 19–400 kDa; degree of deacetylation, 75–98%) has
been evaluated as a directly compressible vehicle for tablets, but has found limited
utility due to the lack of good flow properties and compressibility. The influence of
excipient (lactose, sodium lauryl sulfate, sodium alginate, hydroxypropyl methyl
286
A.K. Anal and A. Tuladhar