Chitosan Microspheres Encapsulated With   Metoprolol Succinate: Formulation and In - Vitro Evaluation


Mohanraj Palanisamy*1, Jasmina Khanam1, N Arun Kumar2 and C Rani2

1 Department of Pharmaceutical Technology, Jadavpur University, Kolkata, West Bengal.

2 Department of Pharmaceutics, Cheran College of Pharmacy, Coimbatore, Tamil Nadu.

*Corresponding Author E-mail:



The rationale of this study was to develop a sustained release microspheres formulation containing metoprolol succinate. The various batches of microspheres were prepared by cross-linking technique using chitosan polymer. The effect of stirring speed and core to coat ratio was studied with respect to entrapment efficiency and micromeritics properties. In vitro release study was performed in phosphate buffer (pH 6.8). Shape and surface analysis are also examined by scanning electron microscope. The microspheres obtained from cross-linking technique were spherical and free flow in nature. The drug content was ranges from 65.62% -72.06%. Entrapment efficiency was based on the ratio of polymer present in formulation. This is due to high loss of drug during formulation. Particle size ranged from 330 to 540µm. Microspheres was spherical in shape and having a smooth surface as the evident in Scanning electron microscopic photographs. Drug crystals was found outer surface of microspheres in formulation F1, whereas, it was absent in F4 (1:5 ratio).  In vitro release study shows a better sustained effect in F3 (1:3 ratio) over 24hrs. The release data was determined using various kinetic models and korsmeyer – peppas model showed an acceptable regression value for all composition. Thus, its follows non -fickians transport mechanism and the drug release was extended up to 96.78% over period of time. This micro particulate system proves the efficient in the delivering of drug in the system over extended period of time with minimal dose.


KEY WORDS:  Chitosan microspheres, metoprolol succinate, processing variables



Metoprolol Succinate (MS) is a β1-selective adrenergic blocking agent. When MS conventional tablets are administered with food rather than on an empty stomach, peak plasma concentrations are higher and the extent of absorption of the drug is increased. The maintenance of a constant plasma level of a cardiovascular drug is important in ensuring the desired therapeutic response. Since the half-life of MS is ~3 to 4 hours 1, multiple doses are needed to maintain a constant plasma concentration for a good therapeutic response and improved patient compliance. Conventional dosage from fails to maintains the drug plasma concentration over the extended period of time.


These result in the frequent administration of a drug with higher dose causes unwanted toxic effects and if they release the entire amount of drug so as to cause dose dumping. Various approaches are made to improve the concentration of drug in the plasma over the extended period of time.


Micro encapsulation (micro particulate delivery system) was one of the promising drug delivery system, which delivers the drugs in the controlled rate over the period of time2, 3. In order to develop the micro particulate system a variety of polymers are used. Among various polymers, chitosan is a natural polysaccharide comprising copolymers of glu-cosamine and N-acetyl glucosamine. Being biodegradable and biocompatible, chitosan has been used in the formulation of particulate drug delivery systems to achieve controlled drug delivery 4. In this present study, chitosan microspheres were encapsulated with the metoprolol succinate, and in vitro characterization was evaluated.



TABLE-1: Effect of Various Formulation Parameters on the Properties of Microspheres

Formulation Parameters


Encapsulation Efficiency* (%)

Particle Size* (µm)

Angle of Repose* (°)


Bulk Density*

(ρb) gm/cm3

Drug – Polymer Ratio



330 ± 3.12

34°65' ± 3°64'

0.435 ± 0.032



395 ± 3.68

29°82' ± 3°40'

0.422 ± 0.062



440 ± 2 .96

28°'34' ± 1°35'

0.391 ± 0.094



495 ± 3.76

28°34' ± 1°35'

0.353 ± 0.083

Stirring speed (rpm)








527 ± 4.583

23°56' ± 3°19'

0.316 ± 0.034



489 ± 4.238

26°47' ± 2°79'

0.359 ± 0.071



435 ± 2.833

28°11' ± 2°13'

0.395 ± 0.016

* Each observation is the mean (± SD) of three determinations.


TABLE-2: Release Kinetics (Regression coefficient r2) of Metoprolol succinate microspheres



Zero Order

First Order


Korsmeyer - Peppas































Metoprolol succinate was received from Polydrug Laboratories, Maharashtra, India (Mol.Wt.652.81) as a donate sample; Chitosan (Mol.Wt 600 000), was obtained from Fluka (Fluka Chemie AG, Buchs, Switzerland); Potassium dihydrogen phosphate and disodium hydrogen phosphate (Merck, Darmstadt, Germany). All other chemicals /reagents used wee of analytical grade.




 Metoprolol succinate was encapsulated by cross linking technique using chitosan polymer. In briefly, 100ml of paraffin oil containing 1ml of span 80 was allowed to stir for 30 minutes. Then the polymeric - drug dispersion was incorporated drop wise with constant stirring at 750rpm. Add 1ml of glutaraldehyde after 5minutes of dispersion incorporation and stirring was continued for 1hour at 750 -1500 rpm). Allow to stand for ˝ hour. Microspheres were settled down slowly in the dispersion. The obtained microspheres were collected by filtration and was twice with diethyl ether, dried at room temperature and stored in desiccators for further evaluation.


Accurately weighed microspheres were pulverized and shaken well with 25ml of 0.1N HCl (pH 1.2) solution. The solution was filtered and then made necessary dilution with 0.1N HCl and absorbance was noted at 280 nm using UV – VIS spectrophotometer. Encapsulation efficiency was calculated by actual drug content / theoretical drug content multiply by 100.



The size of microspheres was determined by the optical microscopy method. The bulk density was measured by


a tapping method. Cohesiveness of particles was determined by funnel method.


Fig-1: Effect of polymer-drug ratio on the cumulative release of Microspheres


Fig-2: Effect of stirring speed on the cumulative release of Microspheres



In vitro drug release from microspheres was performed using the rotating basket method as specified in USP XXIV (Electro Lab, Mumbai) at 50 rpm. Microspheres equivalent to 100mg of metoprolol succinate was wrapped in a muslin cloth and suspended in 900ml of 0.1 N HCl (pH 1.2) kept in the basket and allowed to rotate at 50 r/min. Operating temperature was maintained at 37o ± 1oC. Sample (5ml) was withdrawn at  one hour intervals up to first 2 hr. 5 ml of fresh buffer replaced the withdrawn volume to maintain sink condition. After 2 hr, dissolution medium was replaced by 900ml of fresh phosphate buffer of pH 6.8 and study was conducted till 24th hour as before and samples were withdrawn at 2hr interval. Withdrawal samples were analyzed by UV-spectrophotometer at wavelength 280 nm.


TABLE-3: Results of Drug Content for Formulation (F3) at Various Storage Conditions
























In order to know the drug release mechanism of microspheres, in vitro dissolution data were with various kinetic model equations such as Zero order, First order, Higuchi and Korsmeyer Peppas. Correlation coefficient (r2) values were calculated for linear curves obtained by the regression analysis of the above plot.



Shape and surface morphology for optimized formulation was studied using Scanning Electro Microscope (Jeol JSM – 5610, Japan) at suitable magnification at room temperature.


Stability studies 14:

 The drug loaded microspheres were stored at various storage conditions such as room temperature, 37oC, 45o / 75% RH in sealed container. The drug content was determined spectrophotometrically at 280nm at regular intervals.


Fig-3: SEM Photographs of microspheres



The microspheres encapsulated by cross linking technique were found to be spherical in nature. The effects of formulation parameters on the properties of microspheres were shown in Table 1. The properties of microspheres depend upon the drug: polymer ratio. Good encapsulation was achieved in the formulation 1:3 drug: polymer ratio indicates that 1:3 ratio has potentiality for drug encapsulation. The particle size was increased by increasing the ratio of the polymer. The cohesiveness of particle decreased by increased the polymer ratio. All the formulation shows the better sustained release over the period of time as shown in the Fig 1. The r2 values obtained by fitting with various kinetic models are as shown in the Table 2. Upon fitting with various kinetic model, Korsmeyer – Peppas model equation shows better linear regression coefficient (r2) ranges from 0.9815 – 0.9982. There was no significant change in the drug content even upon subjected to various temperature as shown in the Table 3.



Spherical particles were obtained for the formulation with optimum stirring speed. In the preparation of microspheres by cross linking method involves emulsification followed by cross linking with cross linking agent. The stirring speed plays a vital role in the formation of microspheres by emulsification of dispersing phase into the continuous medium Jeyanthi et al15. These were observed in the formulation varying stirring speed (FS1 – FS3). Spherical particles fail to form in the FS1 formulated with 750 rpm, indicates the lower diffusion pf solvent from dispersing phase into the continuous medium. Among various stirring speed, stirring at 1500rpm shows a uniform formation of microspheres and particles were discrete in nature. Initial stirring also alters the formation of spherical particle, during emulsification process. With low speed of stirring, dispersed phase escaped from the rupture and regain easily. Whereas in the case of higher stirring speed rupture in the dispersion droplets fails to regain the solid state, thus results in the formation of few microspheres. The variation in the drug entrapment was observed in all formulation may due to effect of various formulation parameters such as concentration of polymer and speed of stirring Pralhad T.T et al6. Better entrapment efficiency was achieved by increasing the ratio of the polymer. Among all the formulation, F3 shows the higher entrapment efficiency, when compared to other formulation. Constant entrapment efficiency was observed after increasing the polymer ratio to 1:4 and there was no significant change in the entrapment efficiency of microspheres formulated with respect to different stirring speed. The particle size was increased by increasing the polymer ratio resulted in the Table 1. This may due to higher viscosity of the internal phase leads to formation of larger globule. Increase in the stirring speed would break the dispersion into a fine droplet results in the reduction of particle size. Higher the particle size leads to decrease the cohesiveness and bulk density of the particles, where observed in the formulation containing higher drug: polymer ratio. The drug release from all the formulation was extended up to 24hrs as shown in Fig 1 and Fig 2. The initial burst release was more in the formulation F1 indicates the high amount of free drug crystals present in the microspheres, whereas burst release was reduced in the F4 due to absence of drug crystals on the surface of the microspheres. The release rate was decreased by increasing the concentration of the polymer and the particle size. The rapid release was observed in the formulation F1, due to low concentration of polymer and size of the particle, results in higher contact of dissolution medium due to increased surface area. Among all formulation, 97.21% of drug released in F3 (1:3 drug: polymer ratio) with 1500rpm shows better sustained effect over the period of 24hrs. The drug release mechanism from the microspheres from regression coefficient (Table 2) was erosion based mechanism as plotted against log t vs. log % drug release. When cumulative percentage of drug release vs. time was plotted for zero order release, the straight line were obtained (r2 = 0.9772 – 0.9966) indicated that the drug release followed zero order kinetics. The regression coefficient (r2) obtained from korsmeyer – peppas was in the range of 0.9815 – 0.9982. The n is less than 1 indicating that drug release follows non fickians type of transport mechanism. From overall view of the drug kinetics, we conclude that drug release kinetics varied by the concentration of polymer. From the scanning electron microscopic photographs (Fig 3), we observed the spherical nature with the smooth surface of obtained microspheres. There was no significant change in the drug content and the release of the microspheres after subjected to various storage conditions as shown in Table 3 indicates that the prepared microspheres were stable in nature. From this study, we concluded that the encapsulation of metoprolol succinate with chitosan may be promise in delivering of drug over period of time and thus it improves patient compliance.



The author would like to thank Polydrug Laboratories, Maharashtra for providing metoprolol succinate as a gift sample.



1.      Brain BH. And Robert JL. Catecholamines, sympathomimetic drugs and adrenergic receptor. Goodman and Gilman’s. The Pharmacological Basis of Therapeutics edited by Hardman JG and Limbird LE.Mcgraw – Hill, New York. 1996; 9th edn: pp 238, 1760.

2.      Giovagnoli S, Blasi  P, Ricci M, Schoubben A, Perioli L, Rossi C. Physicochemical characterization and release mechanism of a novel prednisone biodegradable microspheres formulation. J. Pharm Sci. 2008; 97: 303 – 317.

3.      Joseph NJ, Lakshmi S, Jayakrishnan A. A floating-type oral dosage form for piroxicam based on hollow polycarbonate microspheres: in vitro and in vivo evaluation in rabbits. J.Controlled Release.2002; 79: 1–79.

4.      Lewis DH. Controlled release of bioactive agents from lactide /glycolide polymers. In: edited by Chasin M, Langer R, Biodegradable polymers as drug delivery systems. Marcell Dekker Inc., New York: 1990; pp 1 - 41.

5.      Sanju D, Anil KS, and Vivek RS. Evaluation of mucoadhesive properties of chitosan microspheres prepared by different methods. AAPS PharmSciTech. 2004; 5 (4) Article 67.

6.      Pralhad TT, Rajendrakumar DK. Encapsulation of water – insoluble drug by a cross – linking technique: effect of process and formulation variables on encapsulation efficiency, particle size, and invitro dissolution rate. AAPS Pharm SciTech. 2004; 6: (1) Article 12

7.      Muge K, Tamer B. The effect of the drug/polymer ratio on the properties of the verapamil HCl loaded microspheres. Int. J. Pharm. 2003; 252: 99–109

8.      Yilmaz C, Ge J, Stefano G, Kyu-Heum N, and Patrick PD. Preparation and characterization of poly (D, L – lactide – co – glycolide) microspheres for controlled release of human growth hormone. AAPS Pharm Sci Tech. 2003; 4: Article 28.

9.      Upadhye K, Bakhles, Dixit G. Preparation and evaluation of gelatin microspheres containing ciprofloxacin hydrochloride. Ind. Drugs. 2004; 11: 665-669.

10.    USP 26 / NF 21 2003, Asian edition, 1220-1221.

11.    Hamid AM, Harris MS, Jaweria T, and Rabia IY. Once-daily tablet formulation and in vitro release evaluation of cefpodoxime using hydroxypropyl methylcellulose: a technical note. AAPS PharmSciTech. 2006; 7: Article 78

12.    Atsuko F, Ryuta F, Yorinobu Y, and Hisakazu S. Analysis of the release process of phenylpropanolamine hydrochloride from ethylcellulose matrix granules iv.1) evaluation of the controlled release properties for in vivo and in vitro release systems. Chem. Pharm. Bull. 2007; 55: 1569—1573.  

13.    Alf L, Hiromitsu Y, Hirofumi T, Yoshiaki K. Microsphere design for the colonic delivery of 5-fluorouracil. J. Controlled Release. 2003; 90: 313–322.

14.    Vijayalakshmi P, Kusum DV, Narendra C, Srinagesh S. Development of extended zero-order release gliclazide tablets by central composite design. Drug. Dev Ind Pharm. 2008; 34: 33–45.

15.    Jeyanthi R, Mehta RC, Thanoo BC, Deluca PP. Effect of processing parameters on the properties of peptide-containing PLGA microspheres. J Microencapsulation. 1997; 14: 163-174.




Received on 16.12.2008  Modified on 11.02.2009

Accepted on 15.03.2009  © RJPT All right reserved

Research J. Pharm. and Tech.2 (2): April.-June.2009; Page349-352