Chemistry Reference
In-Depth Information
Fig. 9.4
Various modes of drug delivery
metabolic degradation during passage through mucosa and subsequently the liver.
The most prominent among these challenges is the harsh environment of the
stomach, where enzymatic degradation of many drugs like the polypeptides (e.g.,
insulin) takes place. Further, certain drugs like the salicylates can damage the
stomach lining, leading to gastric ulcer. The only solution to this problem is to
enclose the drug in a matrix that protects it during passage through the harsh
environment of the stomach and releases it in the lower gastrointestinal tract.
This gastric bypass can be achieved through the following strategies:
(a) Delayed release formulation: In this case, the matrix releases the drug after a
time delay. This time delay can be adjusted to cover the gastric region transit
time. The matrix in this case essentially consists of cross-linked/grafted
polymers, and the extent of cross-linking/grafting controls the time delay.
(b) pH-triggered drug release: pH of stomach is acidic, while that of lower gastro-
intestinal tract is neutral/alkaline. This difference in pH can act as a trigger for
drug release into the lower gastrointestinal tract (bypassing the gastric region).
Evidently, this involves a drug delivery matrix which does not significantly
release the drug in acidic pH (of stomach) and release it at a much faster rate in
the neutral/alkaline pH (of lower gastrointestinal tract).
(c) Drug release from matrix degradable by colonic micro flora: The drug can be
enclosed in a matrix that is not affected (and can protect the drug) by the
stomach environment, but undergoes biodegradation by colonic micro flora.
