This document discusses gastroretentive drug delivery systems (GRDDS), which are designed to retain a dosage form in the stomach and release the drug in a controlled manner. It begins by outlining the advantages of GRDDS and appropriate candidate drugs. It then discusses various approaches to GRDDS, including high density systems, floating systems, swelling/expanding systems, and mucoadhesive/bioadhesive systems. The document concludes by mentioning some references on GRDDS.

1. ZAHID HUSAIN
M.Pharm (Pharmaceutics)
Faculty of Pharmacy, IU, Lucknow

2. CONTENTS
 INTRODUCTION
 APPROPRIATE CANDIDATE DRUGS FOR
GRDDS
 ADVANTAGES
 LIMITATIONS
 APPROACHES
 CONCLUSION
 REFERENCES

3.  Oral drug delivery is widely used in
pharmaceutical field to treat the diseases.
 Some drugs are absorbed at specific site only
,these require release at that specific site.
 Gastro retentive drug delivery(GRDDS) is one of
the site specific drug delivery for the delivery of
the drugs at stomach.
 It is obtained by retaining dosage form into
stomach and drug is being released at controlled
manner at specific site.

4.  Drugs acting locally in the stomach.
E.g. Antacids and drugs for H. Pylori viz., Misoprostol.
 Drugs that are primarily absorbed in the stomach.
E.g. Amoxicillin
 Drugs that is poorly soluble at alkaline pH.
E.g. Furosamide, Diazepam,Verapamil, etc.
 Drugs with a narrow absorption window.
E.g. Cyclosporine, Levodopa, Methotrexate etc.

5.  Drugs which are absorbed rapidly from the GI
tract.
E.g. Metronidazole, tetracycline.
 Drugs that degrade in the colon.
E.g. Ranitidine, Metformin.
 Drugs that disturb normal colonic microbes
E.g. antibiotics against Helicobacter pylori.

6.  Enhanced bioavailability
 Sustained drug delivery/reduced frequency of
Dosing
 Targeted therapy for local ailments in the
upper GIT
 Reduced fluctuations of drug concentration
 Improved selectivity in receptor activation
 Reduced counter-activity of the body
 Extended effective concentration.
 Minimized adverse activity at the colon.

7.  The drug substances that are unstable in the
acidic environment of the stomach are not
suitable candidates to be incorporated in the
systems.
 These systems require a high level of fluid in
the stomach for drug delivery to float and
work efficiently.
 Not suitable for drugs that have solubility or
stability problem in GIT.

8.  Drugs which are irritant to gastric mucosa are
also not suitable.
 These systems do not offer significant
advantages over the conventional dosage
forms for drugs, which are absorbed through
out GIT.

9.  High-density systems. (HDS)
 Floating systems. (FS)
 Swelling and expanding systems. (SS)
 Mucoadhesive & Bioadhesive systems.(AS)

11.  Gastric contents have a density close to water
(1.004 g cm−3). When the patient take high-
density pellets , they sink to the bottom of the
stomach where they become entrapped in the
folds of the antrum and withstand the peristaltic
waves of the stomach wall.
 A density close to 2.5 g cm−3 seems necessary
for significant prolongation of gastric residence
time.
 Barium sulphate , zinc oxide, iron powder, and
titanium dioxide are examples for excipients
used.

12. These have a bulk density lower than the gastric
content.They remain buoyant in the stomach
for a prolonged period of time, with the
potential for continuous release of drug.
They Include:
 Hydrodynamically balanced systems (HBS)
 Gas-generating systems
 Volatile liquid/ vacuum containing systems
 Raft-forming systems
 Low-density systems

13.  Carbonates or
bicarbonates, which react
with gastric acid or any
other acid (e.g., citric or
tartaric) present in the
formulation to produce CO2
, are usually incorporated in
the dosage form, thus
reducing the density of the
system and making it float
on the media.

14.  Single layer matrix tablet is prepared by incorporating
bicarbonates in matrix forming hydrocolloid gelling
agent like HPMC, chitosin, alginate or other polymers
and drug.
 Bilayer tablet can also be prepared by gas generating
matrix in one layer and second layer with drug for its
SR effect.
 Triple layer tablet also prepared having first swellable
floating layer with bicarbonates, second sustained
release layer of drug and third rapid dissolving layer of
bismuth salt.

15.  System is incorporated with an inflatable chamber
which contains liquid ether -gasifies at body
temperature to cause the chamber to inflate in
stomach.
 Inflatable chamber is loaded with a drug reservoir
which can be a drug, impregnated polymeric then
encapsulated in a gelatin capsule.

16.  Comprised of both an osmotic pressure controlled drug delivery device and an
inflatable floating support in a biodegradable capsule.
 In stomach, the capsule quickly disintegrates and release the intragastric
osmotically controlled drug delivery device .
 Inflatable support forms a deformable hollow polymeric bag containing liquid
that gasifies at body temperature to inflate the bag.
Consists of 2 compartments:
 Drug reservoir
 Osmotically active compartment.

17.  System can be float by flotation chamber,
which may be vacuum or filled with air or a
harmless gas.
 Drug reservoir is encapsulated inside a
microporous compartment.

18.  Prepared by incorporating a high level (2075%w/w) gel forming
hydrocolloids.
E.g.:- Hydroxy ethyl cellulose, hydroxy propyl cellulose, HPMC & Sod.
CMC into the formulation and then compressing these granules into
a tablets or capsules.
 It maintains the bulk density less than 1.

19.  This system is used for delivery
of antacids and drug delivery for
treatment of gastrointestinal
infections and disorders.
 The mechanism involved in this
system includes the formation
of a viscous cohesive gel in
contact with gastric fluids,
forming a continuous layer
called raft.

20.  Polymers used commonly: Polycarbonates,
Cellulose acetate, Calcium alginate, Eudragit
S, agar and methoxylated pectin etc.

21. 1. UNFOLDED SYSTEMS
2. SWELLABLESYSTEMS
The swelling is usually results
from osmotic absorption of
water.
The device gradually
decreases in volume and
rigidity as a result depletion of
drug and expanding agent
and/or bioerosion of polymer
layer, enabling its elimination.

22.  The basis of mucoadhesion is that a dosage form can
stick to the mucosal surface by different mechanisms.
 Examples for Materials commonly used for
bioadhesion are poly acrylic acid, chitosin, Polymethyl
vinyl ether, tragacanth, sodium alginate etc.

23.  N. K. Jain, Gastroretentive drug delivery
systems: Garima Chawla, Piyush Gupta and
Aravind K. Bansal, editors. Progress in
controlled and novel drug delivery systems.
New delhi.
 S.P.vyas, roop K.khar controlled drug delivery
concepts and advances page no.196-217.