Chitosan is a linear polymer of D-glucosamine, [(1-4)-2-amino-2-deoxy-ß-D-glucan], which is a polyaminosaccharide (1). It is obtained by alkaline N-deacetylation of chitin as shown in scheme (1) (2).The exoskeleton of naval crustaceans like crabs, shrimps, and krill are the main sources for the chitin. The availablity of chitin considerd after the cellulose polymer in life(3). Chitosan is safely interface and eliminate from the human body (4). Also, the studies that carried out in Japan permited its use in rations (5).
As mentioned in periodics, in the previous fifteen years. the pharmaceutical uses of chitosan in various types of drug delivery systems are valuable. The causes behind application of this polymer in that concentration result from, its superior biodegradability and biocompatibility, in addition to its postively charge and the ease of contact with it functional moities. Regarding economic, the application of chitosan in pharmaceutical preparations has the ability for competetion against the other avialable. In tablet production, chitosan has been utilized in direct method of manufacturing. Also, it is found that, chitosan increase the rate of dissolution of slightly soluble drugs. Furthermore, it is usefull in the preparation of sustained-release aspirin tablet(4).
Drug Delivery Systems
The drug delivery may be expressed as the uses of material principles to manage the body temporal and spatial position of medicine moities for therapeutic effect. After the drug taken, a minute portion of contained quantity attach the specialised sensory spot and the rest practicaly exhausted by passing into the incorrect organ, eliminated from the required one very fast, or dammeged through the way of coming.
The demand on Drug delivery has been increased excessively in last decades. The actions of polymer in drug delivery system as mentioned in the literatures as follow:
Sustained the activity of drug by dispersion with matrices. 
Targeting the towered the specific tissue such as tumors 
Direct the therapeutic genes into cells 
Window the drug intake at the required position of gastrointestinal tract. 
Control the release of drug at specific temperature or pH. 
The uniform distribution of the loaded drug along the gastrointestinal tract, with minimum local irritation are the main benefits, for microencapsulate solid dosage form. There are differnet techniqes used for the preparation of chitosan microspheres, such as precipitation, anionic cross-linking, chemical cross-linking, thermal cross-linking, co-acervation and emulsification ionic-gelation.
Ciprofloxacin, a fluoroquinolone was used to study the effect of chitosan on the release kinetics. It has strong antibacterial action toword uropathogens with four hours elimination half-life. It is combined with metronidazole to treat the comlexed infections of gastrointestinal tract, diarrhoea caused by infection, typhoid fever (enteric fever), and simple type of gonorrhoea in the cervics and urethra. A formulation of proloned-release ciprofloxacin yelied time coverage as equal as for that produced by two times a day of ordinary rapid drug release, and give a higher blood drug concentration with low within patient changeability(11).
In 1995, another study was conducted using piroxicam as model drug, for the preparation of gel bead of chitosan. This method was considered more valuable in the preparation of sustained-release products. The beads of chitosan containing piroxicam were produced through the complexation of chitosan with sodium tripolyphosphate. The gel spheres were formed, as a result of linking between the postive charge of the amine group in the molecule of chitosan with the negative charge revers ion. A dispersion of piroxicam in 15% w/v of chitosan in acetic acid solution, the resultant was added drop by drop into slowely shaked of 1% w/v tripoly phosphate solution until the pH drived to 5. 1%v/v solution of formuladehyde used for solidifying the product, followed by washing using distilled water within air drying for three succesive times.
The release rate was studied, and the results indicate that it is decreased with an increasing in the molecular weight of chitosan types. Also, the data shown that there is no difference in the release versus time figures among the beads containn various type of chitosan (12).
Another application for chitosan was in mucoadhesive drug delivery systems. Although the poly acrylate polymers are known for their brilliant mucoadhesive possessions. They have the ability to form a hydrgels with mucoadhesive properity, so this type is differ from the other. It can be expected that the present polymers or even the creatised with exterior properties have a mucoadhesion more than that for Polycarbophil gels. The analysis of the data and their related theories, concluded that the mucoadhesive relate to tough hydrogen-bond forming groups such as (-OH, -COOH), strong negative charges, heavy molecular weight, adequate elasticity of polymer chain and possessing a surface energy that favor the distribution on the mucus. Laterely, the last three properities were presented to be possible in theories concerning mucoadhesion. but, more commonly, the known mucoadhesives have the anion and ability hydrogen-bond forming abilities, although, should not be considered a widespread. Instead, polymers with a positive charge and hydrogels it has the capability to build up extra electrostatic with anion of the mucosal membranes(13).
The release of carboxyfluorescein from chitosan capsules were utilized using small changes in the USP basket method. And, the insulin absorption from the intestine was assessed by determining the levels of plasma insulin with its lowering action on the blood glucose after oral route administration of chitosan capsules containing insulin. The carboxyfluorescein release from capsules was identified in simulating gastric fluid (pH 1), or for intestinal fluid (pH 7).
The reaction of chitosan with succinic and phthalic anhydrides individually. The produced semisynthetic polymers were qualified as potential media for colon-site specific, sodium diclofenac was utilized as dispersable drug model for per oral administeration. The resultant matrices were included within tablets, the release rate was studied in vitro, indicate that the release was decreased at the low pH (1) and it was quite well at alkaline media. So, it is concluded that these systems are more usefull to be use in colon site specific release.
The expermental works of chitosan capsules for colon-specific insulin delivery, showed that this system has a resistance action at upper gastrointestinal tract, in contrast, at the rat colon, a metabolism by microorganism. This confirm its capability to act as carrier for targeting the drug towored the colon releas for proteins and non protein drugs.
In addition, chitosan possess the phenomena that make a system with pH dependent release gels as mentioned in the litretures(14).