Hydrogels synthesis of biodegradable hydrogels because of their more

Hydrogels that are
responsive to both temperature and ph can be made simply incorporating
ionisable and hydrophobic functional groups to the same hydrogels. When a small
amount of anionic monomer such as acrylic acid is incorporated in a
thermoreversible polymer, the LCST of the hydrogel depends on the ionization of
pendant carboxyl groups. As the ph of the medium increases above the pka of
carboxyl groups of the polyanions, the LCST shifts to higher temperatures due
to the increased hydrophilicity and charge repulsion. Terpolymer hydrogels
containing NIPPAAm, acrylic acid and 2-hydroxyethyl methacrylate were prepared
for the pulsatile delivery of streptokinase and heparin as a function of
stepwise ph and temperature changes.

Other
Applications

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Ph
sensitive hydrogels have been used in making biosensors and permeation
switches, the ph sensitive hydrogels for these applications are loaded with
enzymes that change the local microenvironment inside the hydrogels. One of the
enzymes used is glucose oxidase that transforms glucose into gluconic acid. The
formation of gluconic acid lowers the local ph, thus affecting the swelling of
ph sensitive hydrogels.

Limitations
and Improvements

One of the
limitations of synthetic ph sensitive polymers is non-biodegradability. For
this reason polymers made up of non-biodegradable polymers are removed from
body after use. The non-biodegradability is not a problem in certain
applications such as in oral drug delivery but it becomes a serious limitation
in other applications such as the development of implantable drug attention has
been focused on the development of biodegradable, ph sensitive hydrogels based
on peptides, proteins and polysaccharides.

Dextran was
activated with 4-aminobutyric acid for crosslinking with 1, 10 diaminodecane
and also grafted with carboxylic groups. The modified dextran hydrogels showed
a faster and higher degree of swelling at high ph conditions and changing the
ph between 7 and 2 resulted in cyclic swelling-deswelling. It is noted that the
dextran hydrogels may not be exactly biodegradable, since the body or certain
sites in body may not have the enzyme to degrade dextran molecules. The natural
polysaccharides are not usually biodegradable in human body.

Synthetic
polypeptides are also used in the synthesis of biodegradable hydrogels because
of their more regular arrangement and less versatile amino acid residues than
those derived from the natural proteins. Example of such synthetic polypeptide
hydrogels include poly aspartic acid poly L-lysine and poly glutamic acid.

Enteric
coated systems

Enteric-coated
formulations are suitable vehicles to modify the release of active substances
such that release at specific target areas in the gastrointestinal tract and
preventing its release in stomach. The major aim of enteric coating is the
protection of drugs that are sensitive or unstable at acidic ph. This is
particularly important for drugs such as enzymes and proteins because these
macromolecules are rapidly hydrolyzed and inactivated in acidic medium.
Macrolide antibiotics such as erythromycin are rapidly degraded by gastric
juices. Acidic drugs like NSAID’s are also enteric coated to prevent local
irritation of the mucosa.

Another
purpose of enteric coating is drug targeting as in case of 5-aminosalicylic
acid or the prodrugs sulfasalazine. In these cases, enteric coating is applied
such that the drug concentration is increased in the lower parts of the GI
Tract. Although the use of enteric coating to achieve modified drug release is
known for long but it has always been criticized as to its true value of
providing protection and targeted release of coated active agents.

Dosage
Forms

In general,
film coated dosage forms can be divided into two forms multiple unit and single
unit dosage forms. Single unit dosage form contains tablets, film coated
capsules and other forms. Multiple units contains granules, capsules, pellets
and compressed film coated particles.

 

 

 

Advantages

Following are the
advantages

1.       Drug directly available at the target site

2.       Decreased dose to be administered

3.       Decreased side effects

4.       Improved drug utilization

5.       Improved patient compliance

6.       Lower daily cost to the patient due to
fewer dosage units are required by the patient in therapy

7.       Protection of mucosa from irritating drugs

8.       Drug loss is prevented by extensive drug
pass metabolism

 

 

Example of novel
drugs

PH-sensitive hydrogels based on polyethylene glycol and
methacrylic acid (MAA) macromonomer (PEGMEMA) entrapping diliazem HCL were
synthesized inside soft gelatin capsules for use as a new dosage form for oral
administration of drug. for the evaluation of their swelling and release
behaviour in two media, different monomers were used:  at ph 7 stimulating the higher ph environment
of the intestine while at low ph stimulating the acid ph of the stomach. Both
the processes DIL-HCL release and swelling are dependant on Ph and composition
of monomer. Hydrogels with intermediate compositions showed diminished DIL·HCl
release at pH 1.2. Similar shaped release profiles were found for the four
hydrogels compositions at ph 7. At this neutral ph slow protonation of the
carboxylate groups of MAA led to the swelling front and a dry core that is
observed by MRI. As a result of this swelling, release curves exhibited a long
period of zero order kinetics. So, this shows that the system could be a
suitable candidate for developing a zero order release dosage form for oral
administration of DIL-HCL. The dissolution and swelling processes were analysed
by different mathematical approaches.

2) the development of a novel colon-specific drug delivery system with
methacrylate derivatives of 5-ASA using drug release properties and PH
sensitive swelling. 5-ASA film coated tablets were prepared for colon specific
delivery. During this method 5-ASA core tablets were first prepared then coated
with dispersion containing Eudragit RS and dessterrifed pectin,
polygalacturonicacidor its sodium and potassium salts. Negligible drug release
occurred during the first five hours where the coated tablets were in small
intestine and stomach. After that, the release of 5-ASA from coated tablets
occurred linearly as a function of time because of the action of pectinolytic
enzymes. 

 

NOVEL COLON SPECIFIC DRUG DELIVERY SYSTEM: A REVIEW

http://www.sciencedirect.com/science/article/pii/S1742706110003375

 

 

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