Konjac glucomannan:
Konjac glucomannan, which is extracted from the tubers of
Amorphophallus konjac is a very promising polysaccharide
for incorporation into drug delivery systems. The konjac
glucomannan molecule consists of D-glucose and Dmannose
linked by 13-1,4 linkage, and the ratio of mannose to
glucose has been reported as 1.6:1, while there is some branching at the C-3 of the mannose unit . Since konjac
glucomannan by itself forms very weak gels, it has been
investigated as an effective excipient in controlled release
drug delivery devices in combination with other polymers or
by modifying its chemical structure. It was shown that konjac glucomannan (KGM) gel systems
were able to maintain integrity and control the release of
theophylline and diltiazem for 8 hours. The Japanese and
European varieties of KGM synergistically interact with
Xanthan gum (XG) giving rise to gel formation; the
synergism being maximum at a 1:1 ratio. By contrast, the
American KGM does not show such effect forming only
viscous solutions. Drug diffusion coefficients of theophylline
and diltiazem HCl, with different molecular size and net
charge, were evaluated in systems containing KGM/XG in the
ratio of 1:1. KGM/XG systems were more efficient than the
XG alone for controlling drug diffusion of small molecules
72 because of the gel formation .
Matrix tablets prepared from konjac glucomannan alone
showed the ability to sustain the release of cimetidine in the
physiological environments of the stomach and small
intestines but the presence of ! mannanase (colon)
accelerated the drug release substantially. Mixtures of konjac
glucomannan and xanthan gum in matrix type tablets showed
high potential to sustain and control the release of the drug due
to stabilization of the gel phase of the tablets by a network of
intermolecular hydrogen bonds between the two polymers to
73 effectively retard drug diffusion .