Controlled on the PH and ionic concentration

Controlled drug delivery systems that are considered
to deliver drugs at predetermined rates for predefined timeframe, have been
utilized to control the limitations of conventional drug formulations. In some
cases drug has to be delivered in response to pH in the body, it would be
invaluable if the medication could be controlled in a way that correctly
matches the physiological needs at appropriate circumstances at the predefined
target sites. The scope of fluids in different sections in the GIT may offer
environmental stimuli that are responsive to drug release ph. Stimuli-responsive
polymers are one of the most important excipients in in DDS and pharmaceutical
formulations. These are designed to produce specific and desired pH
concentration activated response according to body physiological environment
variations.

PH sensitive drug delivery systems (PSDDS) supply the
drug at particular time according to the pathophysiological need of the body
and gives enhanced patient compliance and therapeutic efficacy that is the
reason it is gaining significance.  

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

Polymers

All the PH sensitive polymers consist of pendant
acidic (carboxylic acid and sulfonic acids) and basic (ammonium salts) groups
that either accept or discharge protons in response to changes in environmental
PH. The polymers having substantial number of ionizable groups are called
polyelectrolytes

The charge density of the polymers is dependent on the
PH and ionic concentration of the external solution (in which the polymer is
introduced). Swelling or de-swelling of the polymer can be caused by modifying
the pH of the solution.

pH
sensitive ionization of polyelectrolytes. Poly (acrylic acid) at the top and
poly (N, N-diethylaminoethyl methacrylate) bottom

1.      At
low pH poly-acidic polymers are un-swollen as the acidic groups will be
protonated and hence unionized.

2.      With
increasing pH poly-acidic polymers are going to swell

3.      In
polybasic polymers with diminishing pH ionization of basic group is going to
increase

4.      Derivatives
of acrylic acid are mostly used pH sensitive polymers.

Methodologies for PH Sensitive Drug Delivery

Properties of PH Sensitive Hydrogel and Mechanism

Hydrogels are made up of cross linked polyelectrolytes
that have large differences in swelling properties relying upon the environmental
scale of PH. The pendant acidic or basic groups on polyelectrolytes experience ionization
however it is difficult due to electrostatic effects applied by different
adjacent ionized groups, creating the apparent dissociation constant (ka) completely
different from that of corresponding monoacid or monobase, ionizable groups that
are present on polymer chains leads to swelling of the hydrogels. The swelling
of the polyelectrolyte hydrogels happens due to the electrostatic repulsion that
is among charges present on the polymer chain, the extent of swelling is
affected by means of any condition that lessen electrostatic repulsion such as
pH, ionic strength and counter ions type. The swelling and pH responsiveness of
polyelectrolyte hydrogels can be maintained by usage of neutral comonomers such
as 2-hydroxyethyl methacrylate and methyl methacrylate.

Different hydrophobicity is provided by different
comonomers to the polymer chain, as a result distinct pH sensitive behaviour is
shown.

Example

Hydrogels made up of poly methacrylic acid attached
with poly ethylene glycol have special pH sensitive properties. The acidic
protons of carboxylic acid of PMA at low pH interact with ether oxygen of PEG
via hydrogen bonding resulting in condensation of hydrogels. At high PH the
carboxylic groups of PMA become ionized, the resulting complexation ends up in
swelling of the hydrogels.

Applications of pH sensitive hydrogels

Controlled drug delivery

PH Sensitive hydrogels are usually used to expand
controlled release formulations for oral administration. The pH in stomach
(