Chemistry Reference
In-Depth Information
Table 9.1
pH in various
parts of G.I. tract
Location
pH
Oral cavity
6.2-7.4
Esophagus
5.0-6.0
Stomach
Fast condition 1.4-2.0
Fed condition 3.5-5.0
Small intestine
Jejunum 5.0-6.5
Ileum 6.0-7.5
Large intestine
Right colon 6.4
Mild colon and left colon 6.0-7.4
Fig. 9.6
Cumulative drug release profile of CMG and various graft copolymers for 5-amino
salicylic acid at (
a
)pH
¼
1.4 and (
b
)pH
¼
7.4. The results are mean
SD (
n ¼
3)
tablet disintegrated rapidly in the colon region, releasing the enclosed drug very
fast. This trend for CMG matrix got reflected in its drug release profile (Fig.
9.6
)
and also its corresponding low “
t
50
value” (Table
9.2
). Thus, the native polysaccha-
ride was not found to be suitable as matrix for controlled/sustained drug release of
5-ASA. It is well known that cross-linking/grafting tends to lower solubility of
hydrogels, mainly because of the increase in molecular weight and branching
(grafts) which leads to chain entanglements. Eventually, grafting of PAM chains
onto CMG leads to considerable decrease in solubility. Their drug release profiles
are more sustained compared to CMG as obvious from the figure. Also it is noted
that the higher is the % GE (i.e., lower equilibrium swelling for CMG-g-PAM 6—
Table
9.3
), the more sustained is the rate of drug release, i.e., CMG-g-PAM 6 is the
most ideal matrix for controlled release of 5-ASA. From the drug release profile
(Fig.
9.6
) and their corresponding
t
50
value (Table
9.2
), it is obvious that higher is
the percentage grafting, lower (hence more sustained) is the rate of drug release.
This trend can be explained by the fact that with increase in percentage grafting, the
