Formulation Development and Evaluation of Glibenclamide Microcapsules Using Solvent Evaporation Technique

 

Shivhare UD*1, Kale MK1, Bhusari KP1, Madankar VS1 and Godbole MD2

1Sharad Pawar College of Pharmacy, Hingna Road, Wanadogri, Nagpur-440110.

2Kamla Nehru College of Pharmacy, Borkhedi (Gate), Butibori, Nagpur-441108.

 

ABSTRACT

In  the  present  study,  microcapsules  containing  glibenclamide  were  prepared  by  solvent  evaporation  method  and characterized by sieve analysis and scanning electron microscopy. The microcapsules were analyzed for % encapsulation efficiency, physical properties and in-vitro release pattern. Different batches of microcapsules were prepared by altering the drug:polymer ratio. The size of microcapsules were in the range of 180-250 µ m they were spherical in shape as evidenced by photo micrographs and scanning electron microscopy. The % drug entrapment was in the range of 58-83% and showed sustained drug release over a period of 12 hour.

 

 KEY WORDS     Microcapsules, glibenclamide, solvent evaporation                                                                                               

 

INTRODUCTION:

The basic goal of any therapy is to achieve a steady-state blood or tissue level that is therapeutically effective and non-toxic for an extended period of time. Controlled drug delivery is often used to reduce frequency of dosing, to reduce side effects and thereby obtain a maximum therapeutic effect.

 

One  of  the  methods of  controlling the  rate  of  drug release is by microencapsulation.1 Microspheres can be defined as solid spherical particles ranging from 1 to 5000µ m.  These  particles  consist  of  core  material, which is the drugs and a coating material. The coat material can be of various types ranging from natural polymers, such as albumin, cellulose acetate2, ethyl cellulose, chitosanand synthetics such as poly (vinyl alcohol)4, poly (lactide-co-glycolide)and a combination of two polymers  such as chitosan-sodium carboxy methyl cellulose6, alginate-chitosan7 etc. Glibenclamide is an antidiabetic drug used in diabetic mellitus. Normal dosage regimen varies from 2.5 mg to 20 mg in divided dosage. Biological half life of drug is 3-5 hour. As it requires frequent dosing to maintain the therapeutic effect, it was chosen as a model drug for the present study. Various methods have been reported for microencapsulation, of which solvent evaporation method was utilized to prepare microcapsules, which was characterized by sieve analysis and scanning electron microscopy. From this study, the optimum conditions  for  preparation  of  drug  loaded microcapsules were established and different batches of microcapsules with varying drug: polymer ratios were prepared and they were characterized by sieve analysis and scanning electron microscopy. The microcapsules were analyzed for drug entrapment and in vitro release pattern.

 

MATERIALS AND METHODS:

The  following  materials  were  used  in  the  formulation:

Glibenclamide (APA,  as  a  model  drug,  Somaiya Organa chemicals Pvt. Ltd., Mumbai), Ethyl cellulose (Wockhardt Ltd.)   and   Cellulose   acetate   (Zim   Labs.).   All   other ingredients, such as magnesium stearate, and chemicals used were of A.R. grade.

 

Evaluation of raw materials

Identification   and   Standardization   of   drug   and   other excipients were carried out as per the official procedures mentioned in respective monographs.

 

Microcapsules preparation

Microcapsules preparations using cellulose acetate:

Cellulose acetate (1 gm) was dissolved in acetone (30 ml) and  subsequently glibenclamide (1  gm)  was dispersed in cellulose acetate. Magnesium stearate (0.5 gm) was added into this solution and stirred for half an hour. Mixture was added  in  a  thin  stream  in  the  stirring  500  ml  of  liquid paraffin containing span (4 ml) at 1100 rpm. After 6 hour, the dispersion medium was filtered and prepared microcapsules were washed with several volumes of petroleum ether (60-80 ml) and air-dried. Different batches of microcapsules with varying drug:polymer ratios were prepared by the same procedure.

 

Dissolution testing

Dissolution testing of prepared microcapsules was carried out in dissolution testing apparatus (U.S.P. XXIII) in 7.6 pH phosphate buffer solution. Microcapsules equivalent to 50 mg of glibenclamide were weighed and placed in a rotating basket (100 mesh size). The organ bath was maintained at 370  + 10 and fluid was agitated with stirrer at 100 rpm. Sample solution (2.0 ml) was withdrawn by single mark pipette at regular intervals of time (after every 1 hour) and volume withdrawn (2.0 ml)  was replaced with fresh quantities of  fluid. Sample  was analyzed spectrophotometrically at 203.5 nm.

 

TABLE 1: COMPOSITION AND PHYSICAL CHARACTERISTICS OF MICROCAPSULES

Formulatio
n Code	Drug
(core)	Polymers
(coat)	Drug    :    Polymer
Ratio	Sieve analysis
22/44	%     encapsulation
efficiency	Bulk density
F1	

Glibenclamide	Ethyl cellulose	1:1	89.47	76.80	0.631
F2		
Cellulose acetate	1:1	92.85	83.13	0.633
F3			1:1.5	60.00	80.00	0.625
F4			1:2	66.66	70.00	0.627
F5			1:2.5	95.91	58.20	0.393

 

TABLE 2: IN-VITRO DRUG RELEASE PROFILE OF MICROCAPSULES

Time

in hour

Percent drug released

Formulation

F1

F2

F3

F4

F5

1

12.37

52.21

39.25

36.26

29.21

2

17.88

61.15

40.12

45.26

31.43

3

32.62

69.01

42.92

53.86

43.44

4

42.00

72.37

44.86

56.31

49.13

5

45.28

79.91

58.97

62.69

56.01

6

47.31

85.88

75.71

67.80

58.12

7

56.90

91.20

86.52

70.12

65.16

8

69.15

93.68

89.42

74.32

66.39

9

76.38

95.22

93.56

81.88

67.08

10

77.62

99.64

97.68

88.94

69.01

11

80.53

99.7

98.71

95.05

69.88

12

80.50

99.53

98.47

94.76

68.22

 

manner (99.53%) up  to  12 hour  and  was considered for validation studies. Five different batches of formulation F2 were prepared and were evaluated for physical properties of microcapsules. One-way ANOVA test was applied to study the variance between the batches.

 

Study of drug release kinetics

To   study   the   drug   release   kinetics   of   the   examined microcapsules of  formulation F2,  the  dissolution profiles were analyzed according to zero order, first order, Higuchi’s equation, and Peppa’s equation. Co-efficient of correlation (r) value nearest to I was used for the selection of the most appropriate model.7

 

Study of Physical Properties of Microcapsules

Sieve  analysis:  The  particle  sizes  of  the  prepared microcapsule   were   determined   by   employing   the sieving method.

 

Bulk density: Weighed quantity of the prepared microcapsules was filled in 10 ml graduated cylinder. The initial volume was noted, the cylinder was tapped on wooden surface for three times at the interval of 2 second from the height of an inch. The final volume was recorded and bulk density was calculated from the following formula –

 

Weight of samplein (gm)

 

Fig. 1: In-vitro drug release profiles of glibenclamide loa

 

Scanning electron microscopy (SEM)

The microcapsules were observed under a scanning electron microscope (SEMLeica, JXA-840 A). The microcapsules were mounted directly on to the SEM sample stub, using double-sided sticking tape, and coated with gold film (thickness 200 nm) under reduced pressure (0.001 torr).

 

Stability Studies

Microcapsules were kept in small airtight glass containers

 

Bulk density=

Final volumeafter tapping (cm3 )

and stored at different temperatures at 370  in incubator and at 500 in the oven for a period of 45 days. The samples were analyzed for  percent encapsulation efficiency and  release

 

Percent   encapsulation   efficiency:   Microcapsules

equivalent to 50 mg of glibenclamide were weighed and  crushed,  then  dissolved  in  50  ml  of  phosphate buffer solution (pH 7.6), filtered. This solution (1ml) was diluted to 100 ml with phosphate buffer solution (pH 7.6) to obtain the final solution.

 

Validation

Formulation F2 containing drug and cellulose acetate in 1:1 ratio was found to release the drug in sustained characteristics were studied using dissolution method.

 

RESULTS AND DISCUSSION:

The   purpose   of   the   present   study   was   to   prepare microcapsules of glibenclamide, by using cellulose acetate and ethyl cellulose as coating materials, with the help of solvent evaporation technique. Results of raw material analysis indicated that the  drug, polymers and excipients pass the identification tests specified in official books. The physical parameters of drug as well as excipients concluded that these were considerably good to formulate microcaplues. For the preparation of microcapsules of glibenclamide, cellulose acetate was chosen as a coating polymer, which forms a semipermiable  capsular  film  over  the  encapsulated drug. Solvent evaporation technique was used for the preparation of  microcapsules of  glibenclamide. This technique is easy, less mechanical and do not require expensive equipments as compared to the other techniques.

 

TABLE 3: IN-VITRO RELEASE PROFILE OF GLIBENCLAMIDE LOADED MICROCAPSULES AT pH-7.6

Time

(hour)

In-vitro release profile

F21

F22

F23

F24

F25

2

41.00

42.14

40.29

39.50

42.00

4

59.80

60.18

61.69

59.72

59.87

6

69.72

67.15

66.18

69.97

70.12

8

92.52

92.17

95.42

92.12

96.18

10

99.55

99.48

99.48

99.79

99.61

 

slowed release of drug is due to diffusion of drug from the matrix, which got swollen in medium. Percentage release was calculated from the standard calibration curve of drug in same dissolution medium. The table 2 shows the cumulative percent drug release from glibenclamide microcapsules. Results indicated that there were no significant changes in release amongst the different batches. Thus the formula F2 was found to be better as compared to other.8

 

TABLE 4: IN-VITRO RELEASE KINETIC DATA OF GLIBENCLAMIDE MICROCAPSULES

Formulation

Zero order equation

First order

equation

Higuchi’s equation

Peppas equation

F2

0.3441

0.9381

0.9340

0.9943

 

After  selecting  acetone  as  the  solvent  and  liquid paraffin  as  a  dispersion  medium,  various glibenclamide: cellulose acetate ratio and glibenclamide: ethyl cellulose ratio as 1:1, 1:1.5, 1:2 and 1:2.5 were prepared. They were analyzed for percent encapsulation efficiency. All the formulations showed satisfactory encapsulation efficiency.

 

All the prepared microcapsules of glibenclamide were then subjected to evaluation of its physical properties, in-vitro release profile and stability.

 

After  selecting  acetone  as  the  solvent  and  liquid paraffin  as  a  dispersion  medium,  various glibenclamide: cellulose acetate ratio and glibenclamide: ethyl cellulose ratio as 1:1, 1:1.5, 1:2 and 1:2.5 were prepared. They were analyzed for percent encapsulation efficiency. All the formulations showed satisfactory encapsulation efficiency.

 

In-vitro  drug  release   was   determined  using  USP (XXIII) dissolution apparatus. The dissolution profile of various glibenclamide: cellulose acetate ratios were 1:1, 1:1.5; 1:2, 1:2.5, the drug released were as 99.53 %, 98.47 %, 94.76 %, 68.22 % respectively. And glibenclamide: ethyl cellulose ratio as 1:1 released the drug as 80.50 %, after completion of 12 hour. This indicated that increasing the quantity of cellulose acetate, retarded the drug release to the greater extent due to the increase in the coat thickness. From the in- vitro drug release profile obtained indicated a biphasic pattern i.e. initial fast release of drug called as ‘burst effect’ and later on sustained release. This occurred particularly in case of microcapsules prepared in the core:coat ratio of 1:1 (CA). The initial fast release of drug may be due to surface of microcapsules. Later Size distribution plays a very important role in determining the release characteristics of the microcapsules. Smaller the microcapsules faster will be the release rate of drug from microcapsules. So larger size microcapsules are preferred for production of sustained release products. The size of microcapsule     ranged     between     350-840     µ m.     The microcapsules  of   cellulose   acetate   were   found   to   be spherical and regular.

 

Bulk density is indicative of the package properties of the microcapsules. It has been stated that bulk density values less than 1.2 g/cm3  indicate good flow and values greater than 1.5 g/cmindicate poor flow. It can be seen from the table 1 that, values for bulk density are less than 1.25g/cm3. This  indicates  good  flow  characteristics  of  the microcapsules.

 

Microcapsules prepared in different core:coat ratio were analyzed for its encapsulation efficiency. It was found that percentage entrapment of glibenclamide was between 58-

83% depending on core:coat ratio.

 

Formulation F2 containing drug and cellulose acetate in 1:1 ratio  was  found to  release the  drug in  sustained manner (99.53%) up to 12 hour and was considered for validation studies. Five different batches of formulation F2 were prepared and were evaluated for physical properties of microcapsules (size analysis, bulk density, percent encapsulation efficiency).To the means of results of physical properties of microcapsules of different batches, One-way ANOVA test was applied to check the variance between the batches. One way ANOVA test showed consistent and reproducible results with no significant difference between the batches. Hence, the process was validated and formula F2 was found to be better as compare to other.

 

Study of drug release kinetics

In  order  to  study  the  drug  release  kinetics  of  the  most promising microcapsules, the dissolution profile of F2 was analyzed according to zero order, first order, Higuchi’s and Peppa’s Korsmeyer’s plot respectively. From the table 4, it was observed that, the formulation did not follow a zero order release pattern. When the data was plotted according to first order equation, the formulation showed a fair linearity. Release of drug from microcapsules containing hydrophilic polymers generally involves factors of diffusion and the drug diffusion at a comparatively slower rate as the distance for diffusion increases which is referred as square root kinetics or Higuchi’s kinetics. In our study, the in-vitro release data from the formulation could be best expressed by Higuchi’s equation, as the plots showed high linearity. To confirm the diffusion mechanism, the data were fit into  Korsmeyers  equation,  the  formulation  showed good linearity, indicating that diffusion is dominated mechanism of drug release from the formulation.

 

FIG. 6A: SCANNING ELECTRON MICROGRAPH SHOWING SINGLE UNIFORM MICROSPHERE

 

FIG. 6B: SCANNING ELECTRON MICROGRAPH SHOWING DISCRETE MICROSPHERE

 

Scanning electron microscopy

SEM photographs of cellulose acetate microcapsules indicated that these microcapsules are discrete, spherical, and covered with continuous and smooth coating of the polymer.

 

Stability studies of glibenclamide loaded microcapsules From the above results it was observed that there was no significant    change    in    the    physical    properties    of microcapsules. Both the batches kept at 370 and at 500 were found to have 99.61% and 99.10% of drug release after 10 hour.  Hence,  we  can  say  that,  there  were  negligible differences in the physical properties as well as drug release pattern  of  the  microcapsules  and  the  formulations  were stable

 

TABLE 6: CUMULATIVE PERCENTAGE RELEASE OF GLIBENCLAMIDE FROM VARIOUS BATCHES OF FORMULATION F2

Property

370

500

Bulk density (g/cm3)

0.631

0.630

Percent         encapsulation

efficiency (%)

82.39          ±

0.788

82.20         ±

0.321

 

Time (hour)

370

500

2

40.19

39.82

4

58.72

57.59

6

67.12

66.89

8

92.63

91.32

10

99.61

99.10

 

CONCLUSION:

After summarizing above results, it can be concluded that the ratio 1:1 of glibenclamide and cellulose acetate produced the microcapsules with all desired characteristics like sieve analysis, bulk density, and sustained the release of glibenclamide for extended period of time i.e.12 hour. The cellulose acetate formed the semipermiable membrane over the glibenclamide to give sustained delivery of the glibenclamide.

 

REFERENCES:

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Received on 17.06.2008    Modified on 10.07.2008

Accepted on 15.07.2008   © RJPT All right reserved

Research J. Pharm. and Tech. 1(3): July-Sept. 2008; Page 197-200