GUAR GUM- COLON SPECIFIC PROPERTIES
Colon has recently become accepted area an increasing important site for the drug delivery as it is the site of achieving both the local and systemic drug delivery. Various techniques has been developed for target the drugs to colon, the drugs should reach the colon in a non degraded form. The drugs must first pass through the upper parts of GIT, where the drugs should be stable.
Natural polysaccharides are extensively used in the development of the solid dosage forms for delivery of pharmaceutical drugs to the colon. Most of these natural gums are hydrophilic in nature and causes the premature release of drug. These polysaccharides are get degraded by means of the colonic bacteria1.
Guar gum is the naturally occurring galactomannan polysaccharide derived from the Cyamopsis tetragonolobus. It is made up of linear chain of v-d mannopyranose joined by v-(1-4) linkage with a-D- galactopyranosyl units attached by 1,6- links in the ratio of 1:2.
- It is available in white to yellowish white in colour, odourless
- It gains Film forming property
- Stable at wide variety of PH ranges
- Used as thickening agent also
Guar gum has been used as a
- Polymer drug conjugate,
- Coating agent(compression coating ) and
- Matrix agent.
Guar gum gets hydrates and swells in cold water forming viscous colloidal dispersions or sols. Due of its gelling nature it retards the release of drug from the tablets.Bacteriods & Ruminococcus are responsible for structural breakdown of guar gum.
Guar gum is used to deliver of drugs to the colonic site because of its drug release retarding property and the susceptibility to microbial degradation in the large intestine.
MECHANISM OF DRUG RELEASE:
- POLYMER + DRUG (TABLET)
- RESISTANCE OF POLYMER TOWARD THE ENVIRONMENT OF UPPER PARTS OF GIT
- PASSAGE OF DRUG TOWARDS COLON
- STRUCTURAL BREAKDOWN OF GUAR GUM BY THE COLONIC BACTERIA
- RELEASE OF DRUG
Being of hydrophilic nature of guar gum, it swells in dissolution media causes premature release of drug. So, in order to reduce the enomorous swelling nature of guar gum various chemical modifications of guar gum has been developed in order to increase of hydrophobicity, in some cases it used in formulation by combining with the conventional hydrophobic polymers2.
Various chemical modifications are as follows:
- Phosphate cross linked guar gum
- Borax cross linked guar gum
- Crosslinked carboxymethylated guar gum
- Carbomylmethylated guar gum
- Hydroxy propyl guar gum
Guar gum as Hydrogel was not suitable for colonic drug delivery because of fast delivery. Increases the crosslinking density leads to reduction in solvent uptake.
Borax guar gum is a biodegradable in nature, which is cross linked with borax. The time required to for degradation of this borax guar gum showed that release of drug would be in proximal colon3.
Phosphated cross linked guar gum showed the reduction of enomorous swelling nature of guar gum.
Carboxymethylated guar gum is one of the chemically modified guar gum, which increase the solubility of guar gum, the anionic nature of this carboxymethylated guar gum is when cross linked with the oppositely charged ionic compounds helpful for reduction of swelling nature and promotes colonic delivery4.
Carboxymethylated guar microspheres were also developed by dropping of CMG in divalent or trivalent metal ions. This cross linking nature helps in protecting the drug from environmental conditions of Upper GIT.
The cross linked structures are resistant to dissociation in acidic PH but slowly degrade in intestine. The crosslinking efficiency of trivalent ions was found to be more, due to of higher valency5.
1. Th.F.Vandamme et. al "The use of polysaccharides to target colon" Carbohydrate polymers 4892002) 219-231.
2. Reddy Y.P et., al Review Polymers in colon drug targeting Indian drugs 47(3) March 2010.
3. Sharma, B.R., Kumar, V.,&Soni, P.L.(2004). Carbomylethylation of guar gum. Carbohydrate polymers 58,449-451
4. Vikas et.,al "Investigations on chitosin-Carboxymethyl guar gum complexes interpolymer complexes for colon colon delivery of fluticasone" International journal of Drug delivery 2 (2010) 242-250.
5. VR Sinha et. al Polysaccharides in colon specific drug delivery International journal of pharmaceutics 224 (2001) 19-38.