Preparation and Evaluation of Certain Hydrophilic Drug- Loaded Microspheres

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1 Research Paper Preparation and Evaluation of Certain Hydrophilic Drug- Loaded Microspheres Prof. Dr. Mohamed Aly Kassem 1, Mona Ibrahim Abdel- Tawab El Assal 2 and Aly Al-Saeed Al-Badrawy 3 * 1 Professor of pharmaceutics and Industrial Pharmacy, Faculty of pharmacy - Cairo University 2 Lecturer in Pharmaceutical Technology Department, Faculty of Pharm. Sciences and Pharm. Industries- FUE University 3 Pharmacist in Army Medical Services * ali_badrawy_82@yahoo.com Abstract Microencapsulation is a useful method for prolonging drug release from dosage forms and reducing adverse effects. Recently, dosage forms that can precisely control the release rates and target drugs to a specific body site have made an enormous impact in the formulation and development of novel drug delivery systems. Microspheres are defined as spherical polymeric particles. These microspheres constitute an important part of these drug delivery systems, by the virtue of their small and uniform size and efficient carrier characteristics. It would, therefore, be advantageous to have means for providing an intimate contact of the drug delivery system with the absorbing membranes. This preliminary study shows that optimum polymer concentration, crosslinker concentration and stirring speed are 3%, 7.5% and 400 rpm respectively, the optimum conditions to prepare microspheres by ionotropic gelation with high drug entrapment efficiency are: drug concentration 1.5% w/v, curing time 15 minutes and the concentration of another poly anionic polymer (sodium carboxymethyl cellulose) 0.3% w/v. In phosphate buffer (ph 7.4) the rapid swelling and erosion of the microspheres have greatly contributed in facilitating the drug release rate. Different mathematical models of drug release were obtained for the microspheres indicating that the drug release from the microspheres is controlled by first order kinetics. Keywords: Drug Release, Entrapment Efficiency, Microspheres, Orifice Ionotropic Gelation Technique, Sodium Alginate, Sodium Carboxymethyl Cellulose (Na CMC) 1. Introduction Biodegradable polymers are a newly emerging field. A vast number of biodegradable polymers have been synthesized recently and some microorganisms and enzymes capable of degrading them have been identified. Biodegradable polymers can be defined as natural or synthetic materials capable of adhering to a biological substrate. Such materials can be incorporated in formulations to retain the dosage form at the absorbing epithelial membrane, thereby prolonging drug release and thus decreasing dosage frequency when compared to a more conventional dosage form (Prajapati et al, 2008). It can be achieved by coupling bioadhesion characteristics to microparticles and developing novel delivery systems referred to as bioadhesive microparticles. Bioadhesive microparticles include microspheres and microcapsules (having a core of the drug) of µm in diameter and consisting either entirely of a bioadhesive polymer or having an outer coating of it, respectively (Prajapati et al, 2008). Encapsulation using sodium alginate by orifice ionotropic gelation technique is most often carried out by the dispersion of the alginate/ encapsulant solution onto a gelation medium of calcium chloride. Contact between the alginate and the calcium in solution, induces immediate interfacial ionic polymerization of the alginate via binding of calcium within the cavities of the guluronic residues, Available online at 82

2 thus forming a polyanionic microcapsule (Vandenberg et al, 2001). Two processes can explain the release of a drug from a particle: diffusion and erosion. The drug could diffuse out of the microspheres, following the water phase that fills the matrix of the microspheres. Drug could also be released from the microspheres through the erosion of the matrix (Pourjavadi et al, 2006). In this study, we examined that natural biodegradable polymers such as sodium alginate, sodium carboxymethyl cellulose, can serve the goals of protecting the drugs i.e. ferrous sulphate, ferrous fumarate, from acidic degradation and also act as controlled drug delivery system (Vandenberg et al, 2001). The objectives of this study are to formulate sustained release microspheres by orifice ionic gelation technique using natural biodegradable polymer (sodium alginate) and certain hydrophilic anti-anaemic drugs i.e. ferrous sulphate & ferrous fumarate. In addition to that the purpose of this study was to determine the optimum parameters for alginate microspheres preparation i.e. polymer concentration, crosslinker concentration, stirring speed and improvement of entrapment efficiency of drug loaded alginate microspheres, in vitro drug release from drug loaded microspheres. 2. Materials and Methods 2.1. Materials Sodium alginate (NaAlg), purchased from Al-Shark Al-Awsat Co. (Cairo, Egypt). Calcium chloride dehydrate, purchased from Gama group (Cairo, Egypt). Sodium carboxymethyl cellulose (Na CMC), purchased from Al-Shark Al-Awsat Co. (Cairo, Egypt). 1, 10 phenanthroline (O-Phenanthroline), purchased from Al-Shark Al-Awsat Co. (Cairo, Egypt). Ferrous sulphate heptahydrate and ferrous fumarate were of analytical grade and purchased from Al- Gumhoria Co. (Cairo, Egypt). Marketing capsules as (Fefol-Z, GlaxoSmithKline pharmaceuticals) and (Tandem capsules, US Pharmaceutical Corporation, USA) Methods Determination of Optimum Formulation Conditions Determination of Optimum Polymer Concentration Serial concentrations i.e. 2%, 3%, 4%, 5% w/v, of sodium alginate solution were prepared and then used to formulate microspheres while keeping crosslinker concentration and stirring speed at fixed values i.e. 7.5% w/v and 400 rpm, respectively. Sodium alginate solutions were added to crosslinker solution dropwise using polyethylene syringe (needle size 26 G.) and kept for 30 minutes in this solution. Prepared droplets were stirred, filtered, washed with distilled water and dried in hot air oven at 60 C (Prajapati et al, 2008) Determination of Optimum Crosslinker Concentration Serial concentrations i.e. 2.5%, 5%, 7.5%, 10% w/v, of crosslinker solution were prepared and then used to formulate microspheres while keeping sodium alginate concentration and stirring speed at fixed values i.e. 4% w/v and 400 rpmrespectively (Soni et al, 2010) Determination of Optimum Stirring Speed Stirring of prepared droplets in the crosslinking medium was made at different speeds i.e. 200,400,600 rpm, while keeping sodium alginate solution and crosslinker concentration at fixed values of 4%, 7.5% w/v respectively (Al-Kassas et al, 2007) Determination of Microsphere Diameter (Particle Size) The size of the microspheres was determined using an optical microscope fitted with an ocular micrometer. The ocular micrometer was calibrated with a stage micrometer. The average diameter calculated was obtained from a total of more than 50 microspheres (Das et al, 2008) Determination of Factors Affecting Entrapment Efficiency Determination of Optimum Drug Concentration Serial concentrations i.e. 0.5, 1, 1.5, 1.75 % w/v, of drug solution like ferrous sulphate, ferrous fumarate, were mixed with sodium alginate concentration of 3 % w/v and stirred till homogenous solution formed. This solution was added drop-wise to crosslinker solution i.e. 7.5 % w/v, using polyethylene syringe (needle size 26 G) and kept for 30 minutes in crosslinking solution. Prepared droplets were stirred, at the speed of 400 rpm, filtered, washed with distilled water and dried in hot air oven at 60 o C (Lucinda- Silva et al, 2010). The dried microspheres were estimated by a UV- Spectrophotometric method. Accurately weighed 50 mg of microspheres were suspended in 100 ml of phosphate Available online at 83

3 buffer of ph 7.4±0.1. The resulting solution was kept for 24 hours and was stirred for 15 minutes next day. The solution was filtered, after suitable dilution; the drug content in the filtrate was analyzed at 508 nm (Lucinda- Silva et al, 2010). The obtained absorbance was plotted on the standard curve to get the exact concentration of the entrapped drug. Calculating this concentration with dilution factor, we get the percentage of actual drug encapsulated in microspheres (Lucinda-Silva et al, 2010). The drug entrapment efficiency was determined using relationship as follow: Amt. of Entrapped Drug = Initial Drug Wt. in Microsphers Preparation Drug Wt. Escaped in Gelation Medium Theo. Loading Effici.(%) = Initial Drug wt. / Microspheres wt x 100 Act. Loading Effici. (%) = Entrapped Drug wt. / Microspheres wt x 100 Encapsulation Effici. (%) = Actual Loading / Theoretical Loading x 100 OR Encapsulation Effici. (%) = Entrapped Drug wt. / Initial Drug wt. x Determination of Optimum Curing Time Several solutions of sodium alginate of 3 % w/v), Na CMC of 0.3 % w/v), drug concentration of 1.5 % w/v, were mixed and stirred well till homogenous solution formed. This solution was added dropwise to crosslinker solution (i.e. 7.5% w/v) using polyethylene syringe (needle size 26 G) and kept for 5, 15, 30 minutes in crosslinking solution. Prepared droplets were stirred (400 rpm), filtered, washed with distilled water and dried in hot air oven at 60 o C (Manjanna et al, 2009). The drug entrapment efficiency was calculated as aforementioned before Determination of Optimum Na-CMC Concentration Serial concentrations i.e. 0.1, 0.2, 0.3, 0.4 % w/v solution of Sodium carboxymethyl cellulose (Na CMC) were mixed with sodium alginate concentration of 3 % w/v), drug concentration of 1.5 % w/v) and stirred till homogenous solution wsa formed. This solution was added dropwise to crosslinker solution of 7.5 % w/v using polyethylene syringe (needle size 26 G) and kept for 30 minutes in crosslinking solution. Prepared droplets were stirred at 400 rpm, filtered, washed with distilled water and dried in hot air oven at 60 C (Ma et al, 2008). The drug entrapment efficiency was calculated as aforementioned before Morphological Characterization of Loaded Composite Microspheres The morphology of the prepared microspheres was examined using Scanning Electron Microscopy (SEM) where the samples were mounted directly onto the SEM using double-sided sticking tape and were gold spray coated (Al-Kassas et al, 2007) In Vitro Drug Release Study from the Prepared Formulations Determination of Drug Amount per Unit Weight of Microspheres (Drug Content) Taking high entrapment efficiencies of the two drugs used i.e. ferrous sulphate, ferrous fumarate, and most unimodal distribution of size into account, the microspheres prepared under the optimum experimental conditions and using the best encapsulation parameters were classified into 4 batches as follow: Batch 1: Ferrous sulphate / ca-alginate microspheres Batch 2: Ferrous sulphate / composite (ca-alginate/ Na CMC) microspheres Batch 3: Ferrous fumarate / ca-alginate microspheres Batch 4: Ferrous fumarate / composite (ca-alginate/ Na CMC) microspheres Specific amount (200 mg) of dry microspheres was vigorously stirred in a beaker containing 50 ml of phosphate buffer (ph 7.4) to extract the drug from microspheres. The aqueous solution was then filtered and assayed by UV spectrophotometer at value of 508 nm (Singh et al, 2009). The obtained absorbance was plotted on the standard calibration curve of drug i.e. ferrous sulphate, ferrous fumarate, to get the exact concentration of the drug. Calculating this concentration with dilution factor, we get the percentage of actual drug content in microspheres (Singh et al, 2009) as: Microspheres samples drug free (blank) were also prepared and their aqueous solution was collected and used as blank in UV measurement and the mean value of three replicate determinations is reported In-vitro Release Study The release profiles of ferrous sulphate, ferrous fumarate, from prepared microspheres were examined in three different buffer solutions to mimic the physiological gastrointestinal tract media. The medium of ph 1.2 (900 ml 0.1 N HCL) represents the gastric condition for 2 hours and then the second medium would be of ph 4.5 for 2 Available online at 84

4 hours while the medium of ph 7.4 (simulated intestinal fluid, SIF) for 6 hours represent the intestinal condition. The dissolution process was carried out by using USP paddle dissolution apparatus (Pourjavadi et al, 2006). The drug loaded microspheres (equivalent to 150 mg of the drug) was put into empty soft gelatin capsules in the basket, rotated at a constant speed at 75 rpm and maintained temperature at 37 o C. At scheduled time intervals, the sample (3 ml) was withdrawn and replaced with the same volume of fresh medium. The withdrawn sample was filtered, diluted and estimated for the drug at 508 nm spectrophotometrically (Pourjavadi et al, 2006). The drug release behaviour from the prepared formulations, was compared with commercial sustained release dosage forms i.e. Fefol-Z capsules & Tandem capsules, containing ferrous sulphate (150 mg) and ferrous fumarate (162 mg) respectively Analysis of Kinetic Model of Drug Release from the Prepared Microspheres In order to know the mechanism of drug release from the microspheres, the experimental cumulative release data were fitted on various release models commonly used to describe the release kinetics from microspheres such as: Zero order, First order, Higuchi kinetic models at ph 1.2, 4.5 and 7.4 using multiple linear regression analysis (sigma plot 11 software). The release rate constant (K) and correlation coefficient (r 2 ) close to unity was taken as order of release. The following models were fitted: cumulative % drug release versus time (zero order kinetic model); log cumulative % drug remaining versus time (first order kinetic model) and cumulative % drug release versus square root of time (Higuchi model) (Pourjavadi et al, 2006). 3. Results 3.1. Optimum Formulation Conditions Optimum Polymer Concentration When sodium alginate concentration was increased from 2 to 5 % (w/v) the particle diameter increased from (285±36 µm) to (402±68 µm). From Table 1, for microspheres prepared with sodium alginate solution (3% w/v), showed a unimodal distribution (SD= ±12 µm) with a mean particle diameter of (326 µm), indicating relatively homogeneous size (Chen et al, 2006) Optimum Crosslinker Concentration Table 1 shows that the mean particle size of the microspheres increased with increase in the crosslinker concentration, when crosslinker concentration increase from 2.5% w/v to 7.5% w/v, the mean particle size (mean diameter) was also increased from 332±43 µm to 367±17 µm. However, concentration of the crosslinker above 7.5% w/v caused formation of irregular lumps due to extensive crosslinking of the guluronic acid unit of sodium alginate (Rastogi et al, 2007) Optimum Stirring Speed Table 1 shows that the influence of the stirrer rotational speed during the crosslinking step on particle size was evaluated, and it was shown that increasing the rotational speed decreased the mean diameter of microspheres reaching a minimum at 600 rpm. At 600 rpm, a lower mode value was obtained, but a broader distribution increased the mean size (El-Gebaly, 2002). At 400 rpm, the standard deviation relative to the mean was (SD=13 µm) and at 600 rpm this value increased to be (SD = 44 µm) (Silva et al, 2006) Drug-Unloaded (Free) Calcium Alginate Microspheres under Optimum Conditions The microspheres were prepared by ionotropic external gelation technique. Sodium alginate was dissolved in deionised water at a concentration of 3 % w/v, using magnetic stirring. The dispersion was left for 30 minutes to remove any air bubbles that may have been formed during the stirring process. The bubble free sodium alginate dispersion (50 ml) were added drop wise via a polyethylene syringe (needle size 26 G) into 50 ml of calcium chloride solution (7.5 % w/v) and stirred at 400 rpm for 30 min. The droplets from the dispersion instantaneously gelled into discrete matrices upon contact with the solution of gelling agent (Singh et al, 2009). After specified curing time and stirring speed, the gelled microspheres were separated by filtration, washed with 3 x 50ml volumes of deionised water, finally dried at 60 o C for 2 hours in a hot air oven (Prajapati et al, 2008) Factors Affecting Entrapment Efficiency Optimum Drug Concentration Table 2 shows that an increase of the initial drug concentration caused the increasing of entrapment efficiency from % to 66.8 % for drug concentration of 0.5 % and 1.5 % w/v, respectively, for ferrous fumarate; however the entrapment efficiency for ferrous sulphate increased from % to % for drug concentration of 0.5 % and 1.5% w/v, respectively (Shankar et al, 2009) Optimum Curing Time From Table 2, it was observed that increasing crosslinking time from 5 to 30 minutes, the drug entrapment efficiencies were found to be in the range of 68.5% to Available online at 85

5 76.03% for ferrous sulphate and 61.3% to 68.8% for ferrous fumarate (Manjanna et al, 2009). It was found that constant drug loading was achieved at 15 minutes, with no higher decrease in entrapment efficiency after this curing time i.e. 15 minutes (Manjanna et al, 2009) % as Na CMC concentration increases from 0.1 to 0.3%, while the value is down to 77.4% when the concentration of Na CMC reaches up to 0.4%. Similarly, the entrapment efficiency increased from 70.09% to 75.62% for ferrous fumarate as Na CMC concentration Table 1. Effect of Sodium Alginate Concentration, Calcium Chloride Concentration and Stirring Speed on Particle Size Diameter S. No. Formulation Sodium Alginate Conc. (% w/v) Factors Affecting Particle Size Diameter Calcium Chloride Conc. (% w/v) Stirring Speed (rpm) Mean Diameter (µm) ± SD 1 F ± 36 2 F ± 12 3 F ± 43 4 F ± 68 5 F ± 43 6 F ± 56 7 F ± 17 8 F Irregular shapes 9 F ± F ± F ± 44 Table 2. Effect of Drug Concentration, Curing Time and Na CMC Concentration on Drug Entrapment Efficiency S. No. Formulation Factors Affecting Entrapment Efficiency Entrapment Efficiency (%) Mean Mean Diameter Diameter (µm) ± SD (µm) ± SD Drug Conc. (%w/v) Curing Time (min.) Na CMC Conc. (% w/v) Ferrous Sulphate Microspheres Ferrous Fumarate Microspheres 1 F ±42 348± F ±35 362± F ±27 386± F ±39 411± F ±52 298± F ±36 348± F ±27 377± F ± ± F ± ± F ± ± F ± ± Optimum (Na CMC) Concentration From Table 2, it was revealed that the entrapment efficiency for ferrous sulphate increased from 78.40% to increases from 0.1 to 0.3% while the value is down to % when the concentration of Na CMC reaches up to 0.4 % (Vandenberg et al, 2001). It was found that increasing Na CMC concentration in the sodium alginate Available online at 86

6 solution above 0.3 % w/v, made encapsulation extremely difficult, as the viscous nature of the polymer mixture induced excessive microsphere aggregation caused by the increase of viscosity (Vandenberg et al, 2001) Drug-Loaded Alginate-Na CMC (Composite) Microspheres under Optimum Conditions The microspheres were prepared by ionotropic external gelation technique. Sodium alginate, Na CMC and the drugs i.e. ferrous sulphate, ferrous fumarate were dissolved in deionised water at concentrations of 3%, 0.3% and 1.5% w/v respectively using magnetic stirring. The dispersion was left for 30 minutes to remove any air bubbles that may have been formed during the stirring process. The bubble free dispersion (50 ml) was added drop wise via a polyethylene syringe (needle size 26 G) into 50 ml of calcium chloride solution (7.5% w/v) and stirred at 400 rpm for 15 minutes. The droplets from the dispersion instantaneously gelled into discrete matrices upon contact with the solution of gelling agent (Singh et al, 2009). After specified stirring time and stirring speed, the gelled microspheres were separated by filtration, washed with 3 x 50 ml volumes of deionised water, finally dried at 60 o C for 2 hours in a hot air oven (Prajapati et al, 2008) Morphological Characteristics of Microspheres From Figure 1, the composite microspheres prepared by orifice-ionic gelation method were found to be discrete, spherical and free flowing. The microspheres were uniform in size, with size range of 300 to 450 µm. The drug content was found to be uniform in a batch of microspheres (Singh et al, 2009). the molecular level in the microsphere matrices. In addition, pores with diameter of a few micrometers and severe wrinkles are present. Appearance of spots was observed on the surface of microspheres is attributed to the presence of some drug crystals on surface (Roy et al, 2009 and Singh et al, 2009). Figure 1. Optical Microscopic Image for Alginate Microspheres 3.3. In Vitro Release from Drug Loaded Calcium- Alginate and Composite Microspheres Figure 3 reveals that, for calcium alginate microspheres (Batch 1 & 3), the microspheres show negligible drug release in acidic medium i.e. ph 1.2 (< 10% w/w for Batch 1 & < 8% w/w for Batch 3). For composite (Batch 2 & 4), the microspheres show slightly slower drug release in acidic medium (< 5% w/w for Batch 2 & < 4% w/w for Batch-4) (Dhanaraju et al, 2009). At mild acidic medium of ph 4.5, it was found that the rate of drug release from all batches would be slightly higher than that in the high acidic medium of ph 1.2. Figure 2. SEM for Alginate Microspheres From Figure 2, SEM analysis revealed that acceptable spherical morphology was observed, but also flattened, disk-shaped particles. The surface appears smooth with low porosity. The surface of the microspheres was rough due to higher concentration of drug uniformly dispersed at At alkaline medium ph 7.4, it was found that for calcium alginate microspheres (Batch 1 & 3), the microspheres show prolonged release of the drug at the end of 6 hours. Batch 1 (ferrous sulphate calcium alginate microspheres) releases % and Batch 3 (ferrous fumarate ca-alginate microspheres) releases % of the drug (Dhanaraju et al, 2009). At the same time composite microspheres (Batch 2 & 4) showed better sustainity of the drugs in phosphate buffer; Batch 2 (ferrous sulphate composite microspheres) releases % and Batch 4 releases 82.22% of the drug in the same time and at the same ph (Manjanna et al, 2009) Analysis of Kinetic Model of Drug Release from the Prepared Microspheres Figures 4 & 5, shows the plots of percent of drug released vs t (square root of time). These plots were not linear as Available online at 87

7 first order plots with a correlation factor (r), rather lower than first order but indicating that the drug release mechanism from the microspheres was some how, according to first order kinetics (Pourjavadi et al, 2006). alginate and formation of large droplets during addition of polymer solution to the gelling agent (Manjanna et al, 2009). Increase in particle size was also observed with increase in the concentration of the crosslinker. However, Percent of cumulative release (%) Time (hours) Batch-1 Batch-2 Batch-3 Batch-4 Fefol-Z capsules Tandem capsules Figure 3. In vitro Drug Release Pattern of Microspheres Compared to Commercial Sustained Release Dosage Forms 2.5 Percent (%) of drug remained Time (hours) Figure 4. First Order Plots of Drug Release from Microspheres (*) Ferrous Sulphate Calcium Alginate Microspheres ( ) Ferrous Fumarate Calcium Alginate Microspheres ( ) Ferrous Sulphate Composite Microspheres ( ) Ferrous Fumarate Composite Microspheres 4. Discussion 4.1. Optimum Formulation Conditions The proportional increase in the mean particle size of microspheres increased with the amount of polymer in the formulations. This could be attributed to an increase in relative viscosity at higher concentration of sodium when formulations were tried with higher concentration of crosslinker above (7.5 % w/v), microspheres with irregular shapes were obtained. This could be due to the instant gelling of sodium alginate on addition of calcium chloride (Soni et al, 2010). At high stirring the increased shearing stresses generated in the mixture tended to divide the droplets and finally induced a decrease in the mean particle size (El-Gebaly, 2002). A higher mixing rate (more than Available online at 88

8 600 rpm) did not further reduce the mean diameter, because high turbulence caused frothing and adhesion to container wall (Manjanna et al, 2009). At alkaline medium i.e. ph 7.4, the rapid swelling and erosion of the beads have greatly contributed in facilitating the drug release rate. It has been reported that the swelling Percent of drug released (%) Square root of time (hours) Figure 5. Higuchi Model Plots of Drug Release Mechanism (*) Ferrous Sulphate Calcium Alginate Microspheres ( ) Ferrous Fumarate Calcium Alginate Microspheres ( ) Ferrous Sulphate Composite Microspheres ( ) Ferrous Fumarate Composite Microspheres 4.2. Factors Affecting Entrapment Efficiency It was observed that entrapment efficiency was dependent on initial drug concentration. This behaviour is probably more related to the technological difficulty of preparing a stable suspension at concentrations above of 1.5 % w/v than to the ability of drug incorporation by the alginate microspheres (Shankar et al, 2009). Increasing the crosslinking time resulted in a decrease in the drug entrapment efficiencies, since prolonged exposure in the curing medium caused greater loss of drug through crosslinked alginate microspheres (Manjanna et al, 2009). It is obvious that the addition of Na CMC significantly increased the entrapment efficiencies. The reason for this phenomenon can be explained as Alginate Na CMC complex blocks the large pore of calcium alginate gel matrix (Singh et al, 2009) In-vitro Release from Drug Loaded Calcium- Alginate and Composite Microspheres At acidic medium ph 1.2, the polymer (sodium alginate, Na CMC) would be protonated into the insoluble but swelling form, this displays properties of swelling that explains the low aliquot of the release. The slow release of drug from composite microspheres may be due to the greater viscosity of the gel matrix in dissolution medium or may be due to the fact that the higher porosity of alginate microspheres results in faster release of drugs (Dhanaraju et al, 2009). of microspheres in presence of Ca +2 capturing agent depends on the progressive displacement of Ca +2 ions within the microspheres. It has also been reported that the swelling can be enhanced by the presence of phosphate ions, which act as calcium sequestrant (Manjanna et al, 2009) Analysis of Kinetic Model of Drug Release from the Prepared Microspheres The drug release mechanism from the microspheres was according to first order kinetics (Pourjavadi et al, 2006). In the case of diffusion process, parameters such as the area of diffusion, diffusion path length, porosity, concentration gradient and diffusion coefficient influence the rate of diffusion. In order to have a constant rate of release through diffusion (zero order), the above-mentioned parameters must remain constant. In the case of microspheres, some of these parameters such as porosity and diffusion path length are varying during the release process and hence zero order release was not observed (Pourjavadi et al, 2006). 5. Conclusion 1. The optimum conditions to prepare microspheres, which have most unimodal size distribution, are polymer concentration as 3% w/v), crosslinker concentration as 7.5% w/v and stirring speed should not exceed 400 rpm. Available online at 89

9 2. The optimum conditions to prepare microspheres by ionotropic gelation with high drug entrapment efficiency are: drug concentration 1.5 % w/v, curing time 15 minutes and the concentration of another poly anionic polymer Na CMC 0.3 % w/v. 3. Composite microspheres showed slightly slower drug release in acidic medium. 4. Different mathematical models of drug release were applied for the microspheres indicating that the drug release from the microspheres is controlled by first order kinetics. References Al-Kassas, R.S., Al-Gohary, O.M., and Al-Faadhel, M.M. (2007) Controlling of systemic absorption of gliclazide through incorporation into alginate beads. International Journal of Pharmaceutics, 341, pp Chen, L., and Subirade, M. (2006) Alginate whey protein granular microspheres as oral delivery vehicles for bioactive compounds. Biomaterials, 27, pp Das, M.K., and Maurya, D.P. (2008) Evaluation of diltiazem hydrochloride loaded mucoadhesive microspheres prepared by emulsification internal gelation technique. Acta Poloniae Pharmaceutic -Drug Research, 65, pp Dhanaraju, M.D., Sundar, V.D., Nandhakumar, S., and Bhaskar, K. (2009) Development and evaluation of sustained delivery of diclofenac sodium from hydrophilic polymeric beads. J. Young Pharm., 1, pp El-Gebaly, I. (2002) Development and in vitro evaluation of novel floating chitosan microcapsules for oral use: comparison with non-floating chitosan microspheres. International Journal of Pharmaceutics, 249, pp Lucinda-Silva, R.M., Salgadob, H.RN., and Evangelista, R.C. (2010) Alginate chitosan systems: In vitro controlled release of triamcinolone and in vivo gastrointestinal transit. Carbohydrate Polymers, 81(2), pp Ma, N., Xu, L., Wang, Q., Zhang, X., Zhang, W., Li, Y., Jin, L., and Li, S. (2008) Development and evaluation of new sustained-release floating microspheres. International Journal of Pharmaceutics, 358, pp Pourjavadi, A., Barzegar, Sh., and Mahdavinia, G.R. (2006) MBA-crosslinked Na-Alg/CMC as a smart fullpolysaccharide superabsorbent hydrogels. Carbohydrate Polymers, 66, pp Prajapati, S.K., Tripathi, P., Ubaidulla, U., and Anand, V. (2008) Design and Development of Gliclazide Mucoadhesive Microcapsules: In Vitro and In Vivo Evaluation. AAPS PharmSciTech., 9, pp Rastogi, R., Sultana, Y., Aqil, M., Ali, A., Kumar, S., Chuttani, K., and Mishra, A.K. (2007) Alginate microspheres of isoniazid for oral sustained drug delivery. International Journal of Pharmaceutics, 334, pp Roy, A., Bajpai, J., and Bajpai, A.K. (2009) Development of calcium alginate-gelatine based microspheres for controlled release of endosulfan as a model pesticide. Indian Journal of Chemical Technology, 16, pp Shankar, N.B., Kumar, N.U., and Balakrishna, P.K. (2009) Formulation Design, Preparation and In vitro Evaluation of Mucoadhesive Microcapsule employing control release Polymers to enhance gastro retention for Oral delivery of Famotidine. Int. J. PharmSciTech., 2, pp Silva, C.M., Ribeiro, A.J., Figueiredo, M., Ferreira, D., and Veiga, F. (2006) Microencapsulation of Hemoglobin in Chitosan-coated Alginate Microspheres Prepared by Emulsifi cation/internal Gelation. The AAPS Journal, 7, pp Singh, C., Jain, K.A., Kumar, C., and Agarwal, K. (2009) Design and in-vitro evaluation of mucoadhesive microcapsules of pioglitazone. J. young pharm., 1, pp Soni, M.L., M. Kumar, M., and Namdeo, K.P. (2010) Sodium alginate microspheres for extending drug release: formulation and in vitro evaluation. International Journal of Drug Delivery, 2, pp Vandenberg, G.W., Drolet, C., Scott, S.L., and Noue, J. (2001) Factors affecting protein release from alginate chitosan coacervate microcapsules during production and gastric/ intestinal simulation. Journal of Controlled Release, 77, pp Manjanna, K.M., Shivakumar, B., and Kumar, P. (2009) Formulation of oral sustained release aceclofenac sodium microbeads. International Journal of PharmTech Research, 1, pp Available online at 90