The concept of self-assembling and the interactions involved 11
in gastric acidity, they will be protonated into carboxylic acid (‒COOH) groups that
are stabilized via several polar interactions, thus limiting or decreasing hydration
(Assaad and Mateescu, 2010). The release profile observed with those matrices had
low speed at first (because of protonation), and then, in intestinal fluid, the carboxyl
(‒COOH) is deprotonated and ionized (‒COO
−
), with relatively fast release.
In contrast, in the 2RR system, the carboxyl polymer complexed with multivalent
cations (Ca
2+
) in gastric acidity will still possess higher hydration within the matrix,
maintaining the tablet integrity and allowing the dissolution of active principle,
whereas the disintegrating agent contributes to the initial fast release. Simultaneously
with the fast delivery of a limited amount of the active principle, the carboxyl groups
involved in complexation with multivalent cations are progressively protonated,
thereafter inducing the formation of a stable matrix that slows the release of the active
principle. In the intestinal environment, the matrix is gradually deprotonated, forming
carboxylate, which can interact with the modulating agent (e.g., glucosamine), thus
controlling the release of the active principle at a slower rate.
There are commercial formulations affording two release rates for various
active agents formulated as a bilayer, such as certain forms of acetaminophen (i.e.,
Tylenol
®
). Muscle aches and body pain caplets have a first layer dissolve quickly to
relieve pain fast and a second layer that is time-released to provide extended relief
for the day. With the Ca
2+
-induced assembly of carboxylated excipients such as car-
boxymethyl starch (CM-Starch) providing the release of the active principle in two
rates (2RR), the novelty is that they can be formulated as monolithic devices (Le Tien
and Mateescu, 2014), thus differing in the current biphasic or multilayer tablets. The
modulating agents (a pharmaceutically accepted compound with amino groups) may
prolong the active principle’s release, inducing self-assembling within the matrix. It
is supposed that the amino-modulating agent (i.e., polyvinylpyrrolidone, glucosamine
and its salts, choline, lecithin, phosphatidylcholine, or amino acids such as lysine,
tyrosine, glutamine) will slow the release of active principle by interacting ionically
or by hydrogen binding with carboxylic groups of the excipient (e.g., CM-Starch or
CM-Cellulose) complexed with Ca
2+
. Once the divalent cation (Ca
2+
) is released,
the amino-modulator will stabilize the carboxylic excipient (self-assembling), thus
prolonging the active principle’s controlled release.
In line with the concept of “minor alterations–major changements” in this text-
book, an example is the case of change in chitosan self-stabilization by hydrogen
associations, via mild alterations induced by chitosan N-acylation with adequate fatty
acyl chlorides, into a hydrophobic self-assembly (Le Tien et al., 2003).
1.4.3 Hydrophobic stabilization of excipients and drug release
mechanisms
In terms of monolithic devices, hydrophobic self-assembling found for glycol-palmi-
toyl chitosan by Uchegbu (Noble et al., 1999; Martin et al., 2002) and for an acyl-
chitosan (Le Tien et al., 2003) substantially improved drug delivery profiles.
The N-acylation with acyl chlorides of fatty acids of different increasing chain
lengths (C
6–C
16) enhanced the hydrophobic character of chitosan and made important