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i -retention:

1. Bioadhesive systems
2. Swelling systems
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Certain types of drugs can benefit from using gastric retentive devices. These include:

•Acting locally in the stomach.
• Primarily absorbed in the stomach.
• Poorly soluble at an alkaline pH.
• Narrow window of absorption.
• Absorbed rapidly from the GI tract.
• Degrade in the colon

1. Bioadhesive systems
Bio/mucoadhesive systems are those which bind to the gastric epithelial cell surface or mucin
and serve as a potential means of extending the Gastro retention of drug delivery system (DDS)
in the stomach by increasing the intimacy and duration of contact of drug with the biological
membrane.
A bio/muco-adhesive substance is a natural or synthetic polymer capable of producing
an adhesive interaction based on hydration–mediated, bonding-mediated or receptor mediated
adhesion with a biological membrane or mucus lining of GI mucosal surface.
2. Swelling systems
These are the dosage forms, which after swallowing, swells to an extent that prevents their exit
from the pylorus. As a result, the dosage form is retained in the stomach for a longer period of
time. These systems may be named as plug type systems. Sustained and controlled drug release
may be achieved by selection of polymer of proper molecular weight and swelling of the
polymer retards the drug release.
On coming in contact with gastric fluid, the polymer imbibes water and swells. The
extensive swelling of these polymers is due to the presence of physical/chemical crosslinking in
the hydrophilic polymer network. A high degree of cross linking retards the swelling ability of
the system maintaining its physical integrity for prolonged period. On the other hand, a low
degree of cross linking results in the extensive swelling of the system, succeeded by the rapid
dissolution of the polymer.

3. High density systems
These systems with a density of about 3 g/cm3 are retained in the rugae of the stomach and are
capable of withstanding its peristaltic movements. The only major drawbacks with such systems

is that it is technically difficult to manufacture such formulations with high amount of drug
(>50%) and to achieve a density of about 2.8 g/cm3. It is necessary to use diluents like barium
sulfate, zinc oxide, titanium dioxide, iron powder etc. to manufacture such high density
formulations.
4. Floating drug delivery systems (FDDS)
Floating Drug Delivery Systems (FDDS) have a bulk density lower than gastric fluids and thus
remain buoyant in the stomach for a prolonged period of time, without affecting the gastric
emptying rate. While the system is floating on the gastric contents, the drug is released slowly at
a desired rate from the system. After the release of the drug, the residual system is emptied from
the stomach. This results in an increase in the GRT and a better control of fluctuations in the
plasma drug concentrations.

The Floating drug delivery system (FDDS) can be divided into effervescent and non-
effervescent systems.

(A) Effervescent systems
A drug delivery system can be made to float in the stomach by incorporating a floating chamber,
which may be filled with vacuum, air or inert gas.

i. Volatile liquid containing systems:

These have an inflatable chamber which contains a liquid e.g. ether, cyclopentane, that gasifies at
body temperature to cause the inflation of the chamber in the stomach. These systems are
osmotically controlled floating systems containing a hollow deformable unit. There are two
chambers in the system first contains the drug and the second chamber contains the volatile
liquid.
ii. Gas generating systems:
These buoyant delivery systems utilizes effervescent reaction between carbonate/bicarbonate
salts and citric/tartaric acid to liberate CO2 , which gets entrapped in the jellified hydrocolloid
layer of the system, thus decreasing its specific gravity and making it float over chime. A
multiple unit type of floating pills, which generate CO2, have also been developed. The system
consists of a sustained release (SR) pill as seed, surrounded by double layers.
The inner layer is an effervescent layer containing sodium bicarbonate and tartaric acid.
The outer layer is of a swell able membrane layer containing PVA, shellac etc. Another
effervescent system consisting of a collapsible spring, which controls the release of drug from
the polymer matrix, has also been developed. The common approach for preparing these systems
involves resin beads loaded with bicarbonate and coated with ethyl cellulose. The coating which
is insoluble but permeable, allows permeation of water. Thus, carbon-dioxide is released, causing
the beads to float in the stomach.

(B) on-effervescent systems
i. Colloidal gel barrier systems


Hydrodynamically balanced system (HBS), which contains drugs with gel forming
hydrocolloids, was first designed by Sheth and Tossounian in 1975. These systems incorporate a
high level (20-75%w/w) of one or more gel forming, highly swellable, cellulose type hydro-
colloids, polysaccharides and matrix forming polymers. On coming in contact with gastric fluid,
the hydrocolloids in the system hydrate and form a colloidal gel barrier around its surface. This
gel barrier controls the rate of fluid penetration into the device and consequent release of the
drug.

ii. Microporous compartment systems:
This technology is based on the encapsulation of a drug reservoir inside a micro porous
compartment with apertures along its top and bottom walls. The peripheral walls of the drug
reservoir compartment are completely sealed to prevent any direct contact of the gastric mucosal
surface with the undissolved drug.

iii. Multiparticulate system: Floating Beads
Multi-particulate drug delivery systems are mainly oral dosage forms consisting of a multiplicity of small
discrete units, each exhibiting some desired characteristics. In these systems, the dosage of the drug
substances is divided on a plurality of subunit, typically consisting of thousands of spherical particles
with diameter of 0.05-2.00mm. Thus multiparticulate dosage forms are pharmaceutical formulations in
which the active substance is present as a number of small independent subunits. To deliver the
recommended total dose, these subunits are filled into a sachet.

IV .Microballoons
There are various approaches in delivering substances to the target site in a controlled release
fashion. One such approach is using polymeric Microballoons as carrier for drugs. Hollow
microspheres are known as the Microballoons. Microballoons were floatable in vitro for 12 hrs,
when immersed in aqueous media. Radio graphical studies proved that Microballoons orally
administered to human were dispersed in the upper part of stomach and retained there for three
hr against peristaltic movements.

ADVA TAGES OF GASTRORETE TIVE DRUG DELIVERY SYSTEMS
This type of drug delivery systems is especially very useful in the treatment of the
disorders related to the stomach. As the prime objective of such systems is to produce a
gastro retentive product. Or a product which has an enhanced retention time in the
stomach.
Prolonged gastric retention improves bioavailability, reduces drug waste, and improves
solubility for drugs that are less soluble in a high pH environment.
Gastro retention helps to provide better availability of new product with new therapeutics
possibilities and substantial benefits for patients.

All those molecules with considerably short half-life can be administered in this manner
to get an appreciable therapeutic activity.
This is a primary manner in which the bioavailability of a therapeutic agent can be
enhanced, especially all those drugs which get metabolized in the upper GIT.
They also have an advantage over the conventional system as it can be used to over-
come the adversities of gastric retention time as well as the gastric emptying time. As
these systems are expected to remain buoyant on the gastric fluid without affecting the
intrinsic rate of emptying because their bulk density is lower than that of the gastric
fluids.
The duration of treatment through a single dose, this releases the active ingredient over
an extended period of time.
The active entity is delivered to the site of action, thus minimizing or eliminating the side
effects.

LIMITATIO OF GASTRIC RETE TIO

Floating systems are not feasible for those drugs that have solubility or stability
problems in gastric fluids.
Drugs such as Nifedipine, which is well absorbed along the entire GI tract and which undergo
significant first-pass metabolism, may not be suitable candidates for FDDS since the slow gastric
emptying may lead to reduced systemic bioavailability. Also there are limitations to the
applicability of FDDS for drugs that are irritant to gastric mucosa.
One of the disadvantages of floating systems is that they require a sufficiently high level of fluids
in the stomach, so that the drug dosages form float therein and work efficiently.
These systems also require the presence of food to delay their gastric emptying.





Puneet Gupta (M.Pharm) Neelam Singh (M.Pharm)
guptapuneet18@gmail.com singhneelam16@gmail.com


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