Chitosan microspheres: A potential carrier for drug delivery
08 Nov 2017
Conventional dosage forms of drugs may sometimes lead to undesirable fluctuations in the drug concentration ultimately leading to altered efficacy and safety of the drug. Hence, there is a corresponding need for safer and more effective methods and devices for drug delivery. Consequently, novel drug delivery systems (NDDS) have emerged that offer multiple drug delivery solutions such as: oral drug delivery systems, parenteral and implant drug delivery systems, pulmonary and nasal drug delivery, transmucosal drug delivery, transdermal and topical drug delivery, delivery of proteins and peptides, etc. Newer formulation approaches have been investigated including liposomes, PEGylated nanoliposomes, nanostructured lipid carriers (NLCs), poly(lactide-co-glycolide) (PLGA) nanospheres, chitosan nanoparticles, conjugates, oral solid dispersion, β-cyclodextrin complexs etc.
Chitosan (CS) based drug formulations are being widely used to achieve targeted drug delivery. Chitosan can be adopted in several ways, including as a coating agent, gel former, controlled-release matrix, with desirable properties such as mucoadhesion and permeation enhancement to improve the oral bioavailability of drugs. The microsphere-based therapy facilitates targeted drug release through the choice and formulation of various drug-polymer combinations. The desired release profile is achieved through microencapsulation technology and by varying the copolymer ratio, molecular weight of the polymer, etc. in the microsphere therapy. It increases the life span of active constituents and controls the release of bioactive agents. Microspheres can also be used for controlled release of insoluble drugs because of large surface to volume ratios with their smaller particle size. The system can also be used to improve the bioavailability of degradable substances such as proteins. As a drug carrier, CS has been widely examined for many possible routes of administration due to its favorable biological properties such as nontoxicity, biocompatibility, biodegradability and antibacterial characteristics. The effectiveness of CS microsphere delivery system has been established in several clinical studies such as improved in vitro intraocular bioavailability of ganciclovir, improved in vitro bioavailability of sumatriptan through intranasal route etc.
The release of drugs from CS particulate system involves three different mechanisms: (a) erosion, (b) diffusion, and (c) release, from the surface of particles. Due to its high molecular weight, CS has lower solubility and it forms a high viscous gel layer upon contact with the dissolution medium. The drug release was found to be 75-95% up to 3 hours in the microspheres of CS with 250-500 μm and 56-90% up to 5 hours with microspheres 500-1000 μm
Commercially, CS is produced by deacetylation of chitin- a natural polysaccharide. Also, it has been used by modification of basic structure to obtain polymers with a wide range of properties. N-trimethylene chloride is a modified version and a quaternary derivative of CS with superior aqueous solubility, intestinal permeability as well as a higher absorption of neutral and cationic peptide analogue over a wide pH range. Esters such as, CS succinate, CS phthalate can be prepared with different solubility profile from CS. These forms of esters are insoluble in acidic conditions and provide sustained release in basic conditions.
Chitosan microspheres have several applications in novel drug delivery systems including GI-delivery-systems, colon and intestinal drug delivery, opthalmic drug delivery, oral, buccal and sublingual drug delivery, nasal and transdermal drug delivery, vaginal drug delivery, vaccine delivery system, gene delivery system etc. Recently, it was studied as a new inhaled formulation of pirfenidone (PF) – a pyridine, synthetic compound, used to treat idiopathic pulmonary fibrosis (IPF).
Overall, CS exhibits a wide variety of physicochemical and biological properties. Apart from pharmaceuticals, it has been applied in other industries like agriculture, textile, cosmetics, water management etc. Due to its biocompatibility, non-toxicity, biodegradability and antibacterial characteristics, CS can be an attractive biopolymer for delivering a wide variety of drugs in a controlled/sustained manner, and can be successfully used for site specific drug delivery resulting in enhanced efficacy and safety.
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