Invitro Evaluation and Optimization of Controlled Release Chitosan Beads of Metformin Hydrochloride
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Invitro evaluation and optimization of controlled release chitosan beads of Metformin hydrochloride
Manjisa Choudhury, Tanaya Sarma, Samridh Srivastava, Vino S.
School of Bio Sciences and Technology, VIT University, Vellore - 632014, Tamil Nadu, India
manji.choudhury@gmail.com; +91-9626413610
Abstract
Beads of chitosan, in the free and metformin HCl encapsulated forms were prepared by Chitosan/ TPP polyelectrolyte complex. The particles were further stabilized by crosslinking with glutaraldehyde. The size of the particles was found to be in the range of 1.0 to 2.0 mm. Both free and metformin HCL encapsulated Chitosan beads were analyzed by FTIR, Differential Scanning Calorimetry and X-ray diffraction studies. The rate of drug release was investigated by in vitro dissolution studies using UV spectroscopy. The results indicate that these Crosslinked chitosan beads are capable of controlled and sustained release of meformin HCL upto a maximum time of 12 h in PBS at pH 7.4.
Keywords: Chitosan, Metformin HCl, Controlled drug delivery, In-Vitro release.
Introduction
Large number of active compounds is discovered that could serve as therapeutics but very few candidates show clinical success. Their poor activity in vivo is often due to the reason of their low bioavailability. Bioavailability is basically the rate and the extent at which a drug enters and affects the target tissue (Kidane, 2005). When a drug is administered systemically, its bioavailability is typically low and the concentration of the drug in the blood plasma can quickly drop below a desired effective level which further requires re-administration of the drug. This will result in decreased compliance of the patient and the possibility of an overdose will be increased (Wang 2005).
Alternatives have been taken into consideration to regulate the bioavailability of the therapeutic agents. This is provided by controlled drug delivery systems. In such delivery systems, a polymeric network is used where an active therapeutic is incorporated into this network of polymers in a fashion such that there is release of the drug from the material in a predefined manner (Jogani, 2008). There is a variety of natural and synthetic polymers that have been analyzed as drug carriers (Hoffman, 2002).
Polymers are important in sustained release drug delivery systems because mostly all of the drug delivery system use polymers as carriers. Polymers are categorized majorly into three groups which include mucoadhesive polymer, biodegradable polymers or bioerodible, and soluble polymers (Agoes, 2008). Today, there are a wide variety of multifunctional polymers, which includes permeation-enhancers, enzyme-inhibitor, efflux pump-inhibitor and mucoadhesive (Vigl, 2009).
Chitosan is a multifunctional polymer. The features of chitosan include mucoadhesive properties, permeation-enhancers, and enzyme-inhibitor (Vigl, 2009). Chitosan is obtained from deacetylation of chitin, possessing a free amino group that makes it polycationic in nature (Khan et al., 2002). Its mucoadhesive property is due to the electrostatic interactions between positively charged chitosan and negatively charged mucosal surface. Each monomer of chitosan consists of one primary amino group and two free hydroxyl groups. The free amino group is positively charged and subsequently reacts with the surface/mucus that is negatively charged (Bernkop-Schnurch et al., 2004).
There are various modifications made to enhance the mucoadhesive properties of the existing polymers. One modification is immobilization of thiol groups to the mucoadhesive polymers to form disulfide bonds with cysteine-rich sub domains of mucus glycoproteins. In contrast to the earlier mucoadhesive polymers which were attached to the mucus gel layer through noncovalent bonding, the new generation mucoadhesive polymers are capable of forming covalent bonds to the layer of mucus (Bernkop-Schnurch et al., 2004).
The modification of the thiol group attachment has also been done to chitosan. This is done by immobilizing thiol on chitosan backbone, thus known as thiolated chitosan. This was done to improve the solubility of chitosan, mucoadhesive property, and the property of permeation (Bernkop- Schnurch, 2005). The improved properties of mucoadhesive thiolated chitosan are expected to increase the contact time of the drug in the gastrointestinal tract so that it can increase the bioavailability of the drug.
A drug that has less maximum bioavailability is metformin hydrochloride, a type of blood glucose-lowering biguanide compound. Metformin is widely used for the management of type 2 diabetes therapy. The mechanism of action of metformin hydrochloride is not understood completely yet but still these compounds are known to reduce hepatic glucose output, reducing the rate of intestinal glucose absorption and increasing glucose uptake by muscle cells (McEvoy, 2004). There are many problems associated with Chronic therapy involving metformin hydrochloride (HCl), the most notable being the high dose (1.5 to 2.0 g/day), low bioavailability (60%) and the high incidence of gastrointestinal side effects (30% of cases).
Hence, continued efforts are being made to increase the dosage forms formulation of metformin HCl in order to achieve optimal therapy, especially focusing on the sustained release drug. The formula of this dosage form should be made to stay longer in the stomach, the drug release slowly in order to be absorbed gradually in the intestine. The release of drugs that is slow but complete in the stomach is expected to increase the bioavailability of drugs, lower doses, and reduce side effects in the gastrointestinal tract. Multi-unit formulations such as microparticles for oral use is considered to release the drug at a controlled rate and stay in the stomach for a long time, so to minimize the occurrence of dose dumping (Patel et al.,2006).
Materials and methods
2.1 Materials
Chitosan, Sodium Tripolyphosphate (TPP), Acetic Acid, Metformin Hydrochloride (Mw 165.2) were all commercially available and used as received.
2.2 Preparation of Chitosan Beads
A 5% of aqueous solution of chitosan was dissolved in acetic acid at room temperature under agitation. A total of 10ml of the solution was dropped through a syringe needle into 50ml of crosslinking solution under gentle agitation. The crosslinking solution contained 10% TPP. The beads were further stabilized by crosslinking with glutaraldehyde. The flask was incubated in a shaker for an hour. After a certain time, the beads were separated by filtering and washed with distilled water. The beads were dried in oven for an hour at 60 oC and further kept for drying overnight at room temperature.
2.3 Preparation of standard curve for Metformin Hydrochloride
The absorption spectrum of Metformin HCL as measured using spectrophotometer. The spectrum revealed a peak at 239nm. A standard curve was obtained at 239nm by plotting a graph concentration vs O.D.
2.4 Loading of Metformin Hydrochloride
The model drug (Metformin hydrochloride) was added to a 5% aqueous solution of chitosan prepared by dissolving in acetic acid at room temperature under agitation. A total amount of 20ml of the solution was dropped through a syringe needle into 50ml of crosslinking solution under gentle agitation. The crosslinking solution contained 10% TPP. The beads were further stabilized by crosslinking with glutaraldehyde. The flask was incubated in a shaker for an hour. After a certain time, the beads were separated by filtering and washed with distilled water. The beads were dried in oven for an hour at 60 oC and further kept for drying overnight at room temperature.
2.5 Encapsulation efficiency of drug loaded chitosan beads
The encapsulation efficiency was calculated by weighing 50mg of the drug loaded beads and suspending them in a conical flask containing 25ml of Phosphate Buffer Saline (PBS), pH 7.4. The suspension was incubated on an orbital shaker for 24hrs, 50rpm at room temperature. The concentration of Metformin HCL was determined by measuring the absorbance at 239nm by using UV-Vis Spectrophotometer. Metformin HCL loaded chitosan beads were subjected to in vitro release in PBS.
Encapsulation Efficiency (%) = _________________________ x 100
2.6 Morphological characterization using SEM (Scanning Electron Microscopy)
The surface topography of the prepared beads was analyzed using scanning electron microscope. The chitosan beads were coated with gold film under vacuum using a sputter coater.
2.7 X- ray Powder Diffraction (XRD) Studies
The powder X-ray diffraction patterns were traced employing X-ray diffractometer for the samples using Ni filtered radiation (l=15.4nm, 40kV and 30mA).
FTIR measurements were taken at an ambient temperature. Known amount of samples were grounded thoroughly with Potassium Bromide (KBr) and the pellets were formed under a hydraulic pressure of 600kg/cm2.
DSC analysis of the samples was carried out using a differential scanning calorimeter. The samples were heated under nitrogen atmosphere on an aluminium pan at a heating rate of 200C/min in the temperature range of 50-2000C.
Figure 1: Standard curve plotted between OD values and Metformin HCL concentration
3.2 SEM of Chitosan Beads
[pic]
Figure 2: SEM micrograph of TPP/ Chitosan beads
Crosslinked chitosan beads were prepared and utilized as a carrier for the drug, Metformin HCL. The encapsulation efficiency of Metformin HCL loaded chitosan beads was calculated and found to be 83%.
Various known concentrations of Metformin HCL (drug) solutions were prepared for the analysis in UV-Vis Spectrophotometer. Initially to predict the particular wavelength giving the maximum absorbance for the drug, a scan of its absorption spectra with different wavelength was done. A standard curve was obtained by plotting a graph between OD and concentration of the drug at the wavelength which reveals its maximum absorption. The concentration of the unknown was predicted from the standard plot. The wavelength for maximum absorbance is 239nm.
The chitosan beads were qualitatively analyzed through Scanning Electron Microscopy (SEM). Here, the particles were sprinkled on an adhesive aluminium stab and then was surface coated with gold to a thickness of ~ 300Ao using a sputter coater. The scanning electron micrographs revealed a fairly good spherical form and slightly roughened surface texture of the chitosan beads. The diameter of the beads was in the range of 1 to 2mm.
The XRD, FTIR and DSC analysis was done and the results of these analyses are awaited.
Conclusion
Chitosan is a naturally occurring polysaccharide possessing excellent biodegradable and biocompatible characteristics. It has a unique polymeric cationic character and gel and film forming properties due to which it has been regarded as a potential candidate in the development of drug delivery systems. Chitosan beads were prepared by crosslinking with glutaraldehyde to enhance the stability of the beads. Tripolyphosphate (TPP) is a polyanion and can interact with cationic chitosan with electrostatic forces. Metformin loaded chitosan beads were prepared with an encapsulation efficiency of 83%. The further analyses reveal that this system has a potential application for the controlled release of Metformin HCL.
References
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