Formulation
and Evaluation of Mucoadhesive Microcapsules of Glimepiride
J. Satyanarayana*, A. Pavan Kumar, V. Sai
Kishore and T.E. Gopala Krishna Murthy
Bapatla College of Pharmacy, Bapatla-522101
*Corresponding Author E-mail: juluri.satya@gmail.com
ABSTRACT:
The main objective of this present research is to
achieve oral controlled release of Glimepiride and to enhance the
gastrointestinal resident time, for this purpose mucoadhesive microcapsules
were formulated by employing both ionic gelation method and emulsification
gelation method by using sodium alginate and HPMC as coating polymers.
Formulated microcapsules were properly evaluated and comparision between two
methods were focused. In this present research influence of method on rate of
drug release and concentration of polymer coat on rate of drug release from the
Glimepiride microcapsules were studies. The rate of drug release was found to
be decreased by increasing the concentration of the coat polymer. The rate of
drug release was found to be less for microcapsules formulated by
Emulsification Gelation Method than compared to microcapsules formulated by Ionic
Gelation Method.
KEYWORDS: Glimepiride, HPMC, Sodium alginate, Mucoadhesive
Microcapsules, Emulsification Gelation Method, Ionic Gelation method.
INTRODUCTION:
Drug delivery systems (DDS) that can
precisely control the release rates or target drugs to a specific body site
have had an enormous impact on the health care system. Carrier technology
offers an intelligent approach for drug delivery by coupling the drug to a
carrier particle such as microspheres, nanoparticles, liposomes, etc. which
modulates the release and absorption characteristics of the drug. Microspheres
constitute an important part of these particulate DDS by virtue of their small
size and efficient carrier characteristics. However, the success of these novel
DDS is limited due to their short residence time at the site of absorption. It
would, therefore, be advantageous to have means for providing an intimate
contact of the DDS with absorbing membranes. It can be achieved by coupling
mucoadhesion characteristics to microspheres and developing novel delivery
systems referred to as “mucoadhesive microspheres.1” Glimepiride is
the only third generation sulphonyl urea, which lowers the blood glucose level
in the healthy subjects as well as in patients with type 2 diabetes2.
Glimepiride belongs to biopharmaceutical classification- II with drug pKa: 6.2
showing small intestine as the major absorption site. To enhance the intestinal
residence time and to achieve the oral controlled release of Glimepiride,
mucoadhesive microcapsules were formulated and evaluated
MATERIALS AND METHODS:
Glimepiride was gift sample obtained from
Medley Pharmaceuticals Ltd., Daman Unit , Andheri East, Mumbai, India. Hydroxy
Propyl Methyl Cellulose ( HPMC) 3000-5600cps, Methanal, Hydro Chloric acid,
Sodium Hydroxide, Potassium Di Hydrogen Ortho Phosphate, Calcium Chloride,
Sodium Alginate, Qualigens fine chemicals, Mumbai . All other materials used
were of analytical grade.
PREPARATION OF MICROCAPSULES BY IONIC
GELATION METHOD3,4:
Mucoadhesive alginate beads of Glimepiride
were prepared with a coat consisting of alginate and a Mucoadhesive polymer
HPMC and prepared by ionic gelation process.Sodium Alginate (0.5 g) and
HPMC(0.5 g) were dissolved in purified water to form a homogeneous polymer
dispersion. Core material, Glimepiride (containing equivalent to 1.0 g) was
added to the polymer dispersion and mixed thoroughly to form a smooth viscous
dispersion. The resulting dispersion was added drop wise in to 40 ml of 15% w/v
solution of calcium chloride for ionic gelation (or curing) reaction. The
resulting beads were separated and dried at 45 OC for 12 hrs. In case of 1:1.5,
1:2 and 1:3 core: coat ratios, the corresponding HPMC polymer get varied
respectively.
PREPARATION OF ALGINATE BEADS BY
EMULSIFICATION GELATION
METHOD:
In emulsion gelation technique5
sodium alginate (0.5 g), muccoadhesive polymer HPMC(0.5 g) were dissolved in 32
ml of water. The drug (1 g) was added to the polymer solution and mixed
thoroughly. The polymer dispersion was then added in a thin string to 50 ml of
heavy liquid paraffin contained in a 250 ml beaker, while stirring at 500 rpm
to emulsify the added dispersion as fine droplets. A Remi make medium duty
stirrer with speedometer (RQ 121/D) was used for stirring. Then 20 ml of
calcium chloride solution (15% w/v) was transferred into the emulsion while
stirring at 500 rpm for 15 min to produce spherical microcapsules. The
microcapsules were collected by decantation and washed repeatedly with
petroleum ether. The product was then air dried to obtain discrete microcapsules.
Different proportions of core:coat materials namely 1:1.5, 1:2 and 1:3 core: coat
ratios, the corresponding HPMC polymer get varied respectively.
EVALUATION OF FORMULATED MICROCAPSULES:
Size Distribution and Size Analysis:
For size distribution analysis, 250 mg of
the microcapsules of different sizes in a batch were separated by sieving,
using a range of standard sieves. The amounts retained on different sieves were
weighed. The mean particle size of the microcapsules was calculated by the
formula6.
Evaluation of Flow Properties:
The flow properties7of different mucoadhesive alginate beads were studied by
measuring the angle of repose, bulk density, Tapped Density, compressibility index and
Hausner ratio
Estimation of Glimepiride:
Accurately 100 mg beads were weighed and
transferred in to a mortar. Powdered and dissolved in 100 ml of pH 7.8
phosphate buffer, suitably diluted the absorbance of the resulting solution was
measured at 236 nm8.
Entrapment Efficiency:
Entrapment efficiency was calculated using
the formula
Estimated percent drug content was
determined from the analysis of 100 mg alginate beads and the theoretical percent drug content
was calculated from the employed core:coat ratio in the formulation of alginate beads7.
Wall Thickness:
Wall thickness of alginate beads was determined by the method of Luu et al
using the equation.9
Where h is the wall thickness,
is the
arithmetic mean radius of the alginate beads, d1 is the density of the core material, d2
is the density of the coat material p is the proportion of the medicament in
the alginate beads
SEM Analysis:
The samples for the SEM analysis
were prepared by sprinkling the microspheres on one side of the double adhesive
stub. The stub was then coated with fine gold dust. The microspheres were then
observed with the scanning electron microscope (Leica Electron Optics,
Cambridge, USA) at 10 kv.
Drug Release Studies:
Release of Glimepiride from the alginate
beads, was studied in phosphate buffer of pH 7.810 (900 ml) using
Eight Station Dissolution Rate Test Apparatus (M/s. Electrolab) with a paddle
stirrer at 75 rpm11 and at 37 OC ± 0.5 OC. A
sample of alginate beads (16/22 mesh size (855µ)) equivalent to 8 mg of
Glimepiride was used in each test. Samples were withdrawn through a filter
(0.45) at different time intervals and were assayed at 236 nm2 for
Glimepiride using Shimadzu double beam UV spectrophotometer. The drug release
experiments were conducted in triplicate.
Fig No 1: Release Profiles of Glimepiride
Microcapsules Formulated with HPMC by Employing Ionic Gelation Technique
(♦) IG 1 microcapsules formulated with
core:coat ratio 1:1
(•) IG 2 microcapsules formulated with core:coat
ratio 1:1.5
()
IG 3 microcapsules formulated
with core:coat ratio 1:2
(X) IG 4 microcapsules formulated with core:coat
ratio 1:3
Table No 1: List of Microcapsules Prepared
|
POLYMERS
USED
|
IONIC GELATION TECHNIQUE
|
EMULSIFICATION GELATION TECHNIQUE
|
|
FORMULATION CODE
|
CORE:COAT
|
FORMULATION CODE
|
CORE:COAT
|
|
Sodium alginate
+
HPMC
|
IG-1
|
1:1
|
EG-1
|
1:1
|
|
IG-2
|
1:1.5
|
EG-2
|
1:1.5
|
|
IG-3
|
1:2
|
EG-3
|
1:2
|
|
IG-4
|
1:3
|
EG-4
|
1:3
|
Table No 2: Physical Properties of
Glimepiride Beads Prepared with HPMC by Empolying Ionic Gelation Technique.
|
Formulation
|
Angle
of repose
|
Bulk
Density
(
g/cm3)
|
Carr’s
Index
|
Hausner
Ratio
|
Average
Particle Size(µ)
|
%
Drug Content
|
%
Encapsulation
Efficiency
|
|
IG-1
|
16.17
|
0.905
|
21
|
1.27
|
690.89
|
46.38
|
92.76
|
|
IG-2
|
19.21
|
0.712
|
27
|
1.38
|
702.12
|
37.45
|
93.62
|
|
IG-3
|
22.82
|
0.928
|
20.7
|
1.26
|
740.89
|
31.35
|
94.05
|
|
IG-4
|
25.1
|
0.841
|
20
|
1.24
|
789.71
|
24.06
|
96.24
|
Table No 3: Release Kinetics of Glimepiride
Microcapsules Formulated with HPMC by Employing Ionic Gelation Technique
|
Formulation
|
Correlation Coefficient Values
|
n
value
|
Release Rate Constant
(mg/hr) Ko
|
Wall Thickness
(µ)
|
Permeability Coefficient
(µ.mg/hr)
|
|
Zero Order
|
First
Order
|
Higuchi
Model
|
Peppas
Model
|
|
IG-1
|
0.9932
|
0.8964
|
0.9058
|
0.9941
|
1.0157
|
0.52
|
27.48
|
14.37
|
|
IG-2
|
0.9973
|
0.8474
|
0.9043
|
0.9978
|
1.0508
|
0.46
|
38.29
|
17.69
|
|
IG-3
|
0.9961
|
0.8238
|
0.8979
|
0.9983
|
1.0817
|
0.42
|
45.42
|
19.26
|
|
IG-4
|
0.9946
|
0.7977
|
0.8909
|
0.9993
|
1.1864
|
0.39
|
55.69
|
21.50
|
Table No 4: Physical Properties of
Glimepiride Beads Prepared with HPMC by Empolying Emulsification Gelation
Technique
|
Formulation
|
Angle of repose
|
Bulk Density
( g/cm3)
|
Carr’s
Index
|
Hausner
Ratio
|
Average Particle Size(µ)
|
% Drug Content
|
% Encapsulation
Efficiency
|
|
EG-1
|
15.37
|
1.2
|
20
|
1.25
|
540.26
|
45.18
|
90.36
|
|
EG-2
|
18.75
|
1.012
|
25.0
|
1.33
|
580.34
|
36.91
|
92.27
|
|
EG-3
|
20.07
|
1.2
|
25
|
1.30
|
600.48
|
31.45
|
94.35
|
|
EG-4
|
23.33
|
0.911
|
25.9
|
1.28
|
650.42
|
24.12
|
96.48
|
Table No 5: Release Kinetics of Glimepiride
Microcapsules Formulated with HPMC By Employing Emulsification Gelation
Technique
|
Formulation
|
Correlation
Coefficient Values
|
n
value
|
Release
Rate Constant
(mg/hr)
Ko
|
Wall
Thickness
(µ)
|
Permeability
Coefficient
(µ.mg/hr)
|
|
Zero Order
|
First
Order
|
Higuchi
Model
|
Peppas
Model
|
|
EG-1
|
0.9992
|
0.8671
|
0.9324
|
0.9984
|
0.9513
|
0.45
|
27.48
|
12.36
|
|
EG-2
|
0.9995
|
0.8248
|
0.9246
|
0.9996
|
0.9837
|
0.44
|
38.29
|
16.84
|
|
EG-3
|
0.9998
|
0.8127
|
0.9225
|
0.9991
|
1.0043
|
0.38
|
45.42
|
17.25
|
|
EG-4
|
0.9997
|
0.7791
|
0.9176
|
0.9986
|
1.0797
|
0.34
|
55.69
|
18.93
|
Fig No 2: Release Profiles of Glimepiride Microcapsules
Formulated with HPMC by Employing Emulsification Gelation Technique
(♦) EG 1 microcapsules formulated with
core:coat ratio 1:1
(•) EG 2 microcapsules formulated with core:coat
ratio 1:1.5
()
EG 3 microcapsules formulated
with core:coat ratio 1:2
(X) EG 4 microcapsules formulated with core:coat
ratio 1:3
Fig No 3 : SEM Photographs of Glimipiride
Microcapsules Formulated with HPMC By Employing Different Techniques.
a) Ionic Gelation Technique.
b) Emulsification Gelation Technique.
In-vitro Wash-off Test:
The mucoadhesive property of the microspheres was evaluated by an in vitro
adhesion testing method known as the in vitro wash-off method. Freshly
excised pieces of intestinal mucosa (2×2cm) from sheep were mounted onto glass
slides (3 × 1 inch) with cyanoacrylate glue. Two glass slides were connected
with a suitable support. About 50 microspheres
were spread onto each wet rinsed tissue specimen, and immediately thereafter
the support was hung onto the arm of a USP tablet disintegrating test machine.
When the disintegrating test machine was operated, the tissue specimen was
given a slow, regular up-and-down movement in the test fluid at 37°C contained
in a 1 L vessel of the machine. At the end of 30 minutes, at the end of 1 hour,
and at hourly intervals up to 8 hours, the machine was stopped and the number
of microspheres still adhering to the tissue
was counted. The test was performed at both gastric pH (0.1N HCl, pH 1.2) and
intestinal pH (phosphate buffer, pH 7.8).
RESULTS AND DISCUSSIONS:
Produced microcapsules are showing good flow
properties and drug content, % encapsulation was showed in Table No 2 and 4.
The wash off test was relatively rapid in phosphate buffer than in acidic
fluid. The results of wash off test show fairly good mucoadhesive property see
Table No 7. When the amount of drug release values were plotted against time
straight lines were obtained in all the cases indicating that the rate of drug
release from these microcapsules followed zero order kinetics. To ascertain the
mechanism of drug release from various microcapsules plot of log %Released vs
log time (peppas plots) were drawn. The plots were found to be linear with all
microcapsules and the exponential coefficient values 0.9513 to1.186 indicating
non-fickian transport release mechanism. The results indicated that the release
rate was found to decrease with increase in concentration of coating material
applied. The wall thickness of microcapsules was found to be increased with the
increase in concentration of coating material applied. There exists a good
correlation ship in between wall thickness and release rate constant.
COMPARISION OF IONIC GELATION AND
EMULSIFICATION GELATION TECHNIQUES:
To compare ionic gelation and emulsification
gelation techniques the microcapsules formulated with 1:3 core: coat ratio and
having a size of 16/22 mesh (855µ) were compared. The microcapsules formulated
with ionic gelation and emulsification gelation techniques showed significant
differences in their release rate and permeability coefficient values.
Emulsification gelation techniques was found to be more suitable for sustained
release as it yielded slow release of the drug glimepiride and offered low
permeability coefficient.
Table
No 6: COMPARISION OF THE GLIMEPIRIDE MICROCAPSULES PREPARED WITH HPMC.
|
SODIUM
ALGINATE+
MUCOADHESIVE
POLYMER
|
REGRESSION EQUATION
(IONIC
GELATION)
|
REGRESSION
EQUATION
(EMULSIFICATION
GELATION)
|
RELEASE RATE
CONSTANT KO (mg/hr) (IONIC GELATION)
|
RELEASE RATE
CONSTANT KO(mg/hr) (EMULSIFICATION GELATION)
|
|
HPMC
|
y = -0.004x +
0.642
|
y = -0.004x +
0.576
|
0.39
|
0.34
|
Table No 7: In vitro Wash-Off Test
Data of Glimepiride Microcapsules Formulated with HPMC by Employing Different
Techniques
|
Formulations
|
Percent of
Alginate Beads Adhering to Tissue at 5 Times (hr)
|
|
0.1N HCL, pH
1.2
|
Phosphate
Buffer , pH 7.8
|
|
1
|
2
|
4
|
6
|
8
|
1
|
2
|
4
|
6
|
8
|
|
IG-1
|
70
|
65
|
61
|
54
|
50
|
83
|
80
|
75
|
70
|
65
|
|
IG-2
|
72
|
68
|
65
|
58
|
52
|
85
|
82
|
78
|
72
|
68
|
|
IG-3
|
74
|
70
|
68
|
60
|
54
|
90
|
85
|
82
|
78
|
72
|
|
IG-4
|
76
|
72
|
65
|
62
|
54
|
92
|
88
|
84
|
80
|
76
|
|
EG-1
|
73
|
69
|
65
|
64
|
60
|
86
|
85
|
82
|
80
|
74
|
|
EG-2
|
76
|
72
|
67
|
62
|
58
|
88
|
84
|
81
|
78
|
76
|
|
EG-3
|
78
|
74
|
70
|
64
|
61
|
96
|
88
|
84
|
82
|
80
|
|
EG-4
|
80
|
78
|
72
|
68
|
66
|
94
|
90
|
86
|
84
|
82
|
|
ETHYL
CELLULOSE
|
85
|
60
|
20
|
---
|
---
|
87
|
65
|
22
|
---
|
----
|
CONCLUSION:
The rate of drug release, permeability
characteristics and mucoadhesive properties was also influenced by type of the
method adopted for the formulation. Emulsification gelation technique is much
preferable technique, to prepare microcapsules as it yielded less permeable and
more mucoadhesive microcapsules. Ionic gelation method < Emulsification
gelation method.
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