Microencapsulation and InvitroCharacterization of Acrylate Microspheres for Controlled Release of Ambroxol Hydrochloride
Hemant H Gangurde*, Nayana S Baste, Mayur A Chordiya, Chandrasekhar
D Upasani
Department of Pharmaceutics, SSDJ College of Pharmacy, Nasik,
Maharashtra, India
*Corresponding author: Hemant H Gangurde, SSDJ College
of Pharmacy, Neminagar, Chandwad-423 101, Nasik, Maharashtra, India. Tel:
+919423115957; Email: hhgangurde@gmail.com
Received Date: 10 December, 2016; Accepted Date: 25
December, 2016; Published Date: 03 January, 2017
The aim of
present study was to formulate microspheres of Ambroxol hydrochloride by solvent
evaporation technique using acrylic polymers Eudragit RS100 and Eudragit RL100.
Both the polymers were compared for microencapsulation efficiency, drug content
and in vitro drug release. X-RD, DSC
and FTIR confirmed the absence of any drug polymer interaction. All the batches
yielded microspheres with excellent topographical characteristic. The results
of two ways ANOVA suggested statistically significant effect of aluminium tristearate
and polymer concentration on encapsulation efficiency and drug release.
Keywords: Ambroxol
hydrochloride; Eudragit RS100; Eudragit RL100; Solvent Evaporation Method
Introduction
Ambroxol is an active N-desmethyl metabolite of the mucolytic
bromohexine. It is indicated for acute and chronic disorders of respiratory
tract, where there is copious thick secretion or mucus production. It has
biological half-life of 3-4 h. It is absorbed in throughout GIT. Its
bioavailability is 70-72%. Usual initial dose of Ambroxol hydrochloride is 30
mg three times a day. Therefore, to reduce frequency of dosing as well as to
increase bioavailability and enable better compliance, formulating sustained
release dosage form is necessary [1-3]. In literature several sustained release formulations of Ambroxol
hydrochloride have been reported that are based on tablet, capsule or sol
dosage forms allowing once daily administration
[4-7].
In the present study, we examine the potential for the sustained
delivery of Ambroxol by forming microspheres. These multiparticulate solid
dosage forms have a number of advantages such as more uniform distribution of
the drug in the gastrointestinal tract, more uniform drug absorption, reduced
local irritation and elimination of unwanted intestinal retention of polymeric
material [8].
Microencapsulation of hydrophilic drugs have one major
disadvantage of low loading efficiency. One method of ensuring high entrapment
efficiency of is to use W/O emulsion solvent evaporation method which having
hydrophobic processing medium [9]. Eudragit RL100 and Eudragit
RS100 are hydrophobic copolymers synthesized from acrylic acid and methacrylic
acid esters, with RL having higher content of functional quaternary ammonium
groups than RS [10].
Percentage Yield Value of
Microspheres
The percentage yield value of microspheres was determined from
the ratio of amounts of solidified total microspheres to total solid material
used in the inner phase, multiplied by 100.
Drug Entrapment Efficiency
Weighed quantity of microspheres were crushed and suspended in
distilled water to extract drug. After 24 h, filtrate was assayed
spectrophotometric ally at 244.4 nm for drug content. The encapsulation
efficiencies were calculated by using following relationship:
Encapsulation efficiency = (Drug entrapped /Theoretical drug content)
× 100 (1)
Average particle diameter and size distribution of microspheres
were determined by laser diffractometry using a Mastersizer Micro V
2.19(Malvern Instruments, Malvern UK). Approximately 10 mg of microspheres were
dispersed in 10 ml distilled water containing 0.1% tween 80 for several minutes
using an ultrasonic bath. Then aliquot of the microspheres suspension was added
into recirculation unit, which was subsequently circulated 3500 times per
minute. Each sample was measured in triplicate for the analysis. Particle size
was expressed as equivalent volume diameter. The particle size distribution was
also expressed in terms of SPAN factor determined as:
SPAN = d 90- d 50 (2)
d 10
Where d10, d50 and d90 are the diameter sizes and the given percentage value is
the percentage of particles smaller than that size. A high SPAN value indicates
a wide size distribution [12].
Scanning Electron Micrography (SEM)
The microspheres were scanned using scanning electron microscope
(Leica-Stereoscan-440). For the SEM, the microspheres were mounted directly on
to the SEM sample stub using double sided sticking tape, and coated with gold
film thickness of 200 mm under reduced pressure of 0.001 mm of Hg. The shape
and surface characteristic of the microspheres was observed under electron
micro analyzer and photographs were taken using SM 4504 camera.
X-Ray Diffractometry (XRD)
X-ray powder diffractometry was carried out to investigate the
effect of microencapsulation process on crystallinity of drug. Powder XRD was
carried out using XRD (Philips-PW-1050) with filter Ni, CuKa radiation, voltage 40 kV
and a current of 20 mA. The scanning rate employed was 1°/min over the 5° to 50° diffraction angle (2q)
range. The XRD patterns of drug powder, polymer, aluminium tristearate and
drug-loaded microspheres were recorded.
Differential Scanning
Calorimetry (DSC)
The DSC analysis of pure drug, polymer, aluminium tristearate and
drug-loaded microspheres were carried using DSC (Mettler TC 11, TA Processor)
to evaluate any possible drug polymer interaction. The samples (6 mg each) were
placed into a pierced aluminium sample container. The studies were performed
under a static air atmosphere in the temperature range of 50°C to 500°C, at a
heating rate of 10°C/min.
The peak temperatures
were determined after calibration with standard.
Fourier-Transform Infrared Spectroscopy
Drug-polymer interactions were studied by FTIR spectroscopy. The
spectra were recorded for pure drug, polymer, aluminium tristearate and
drug-loaded microspheres using FTIR spectrophotometer (Jasco FTIR-410). Samples
were prepared in KBr disks (2 mg sample in 200 mg KBr). The scanning range was
400-4000 cm-1 and the resolution
was 2/cm.
Drug Release Studies
Microspheres equivalent to 75 mg Ambroxol hydrochloride were
filled in a capsule [13] and in vitro drug release was
studied using USP Apparatus I with 900 ml of dissolution medium at 37.5±0.1°C for 12 h at 100 rpm. 0.1N HCl (pH 1.2) was used as dissolution
medium for the first 2 h, followed by pH 6.8 phosphate buffers for further 10
h. 5 ml of sample was withdrawn after every hour, and was replaced with an
equal volume of fresh dissolution medium. Collected samples were analyzed at
244.4 nm by spectrophotometric ally. The study was performed in triplicate.
Dissolution study was also conducted for marketed capsule MucoliteR SR. (M1)
Release Kinetics
Data obtained from in vitrorelease studies were fitted to various kinetics equations [14] to find out the mechanism of drug release from
microspheres. The kinetics models used were zero order, first order, Higuchi
models, and Baker Lonsdale. The rate constants were also calculated for the
respective models.
Results and Discussion
Microspheres Morphology and
Drug Encapsulation
The shape and surface morphology of microspheres were observed
by scanning electron microscopy. Eudragit RS100 microspheres have spherical,
discrete, non-porous structure with rugged polymeric surface (Figure 1) whereas Eudragit RL100 microspheres were spherical,
discrete, with distinct pores on the surface and also showed accumulation of
free aluminium tristearate particles on the surface. (Figure 2)
The method showed good encapsulation efficiency. Percent drug
encapsulated was found to be in a range of 82-95% for Eudragit RS100, and
76-93% for Eudragit RL100. From (Table 2) data it was observed
that with increase in polymer concentration drug encapsulation efficiency was
increased. Eudragit RL100 showed low encapsulation efficiency as compared to
Eudragit RS100 because it is more permeable than RS100. Drug encapsulation
efficiency was slightly increased as the aluminium tristearate concentration
was increased because dispersing agent reduces the interfacial tension between
the two immiscible phases of the emulsion and reduces the extent of collision
and coalescence between the microspheres during their solidification[15].
Effect on Particle Size
Particle size analysis done by laser diffraction revealed that
Eudragit RS100 microspheres were in the range of 26.62- 43.01 mm with SPAN factors ranging
between 1.24-1.64 whereas Eudragit RL100 microspheres were in the range of
23.08- 44.18 mm with SPAN factors ranging
between 1.32-1.59. (Table 2) It was found that
the size of microspheres was increased as the concentration of inner phase
polymer was increased while the concentration of dispersing agent was kept
constant. Because this increased concentration of polymer solution increases
viscosity of inner phase droplets and gives difficulty in dispersion and subdivision
of droplets[14]. But the variations of the concentrations of aluminum
tristearate did not affect the particle size of microspheres. SPAN factors for
all the batches ranges in between 1.24-1.64, which indicates narrow size of
distribution.
In vitro Drug Release
In vitro dissolution
results showed that the microspheres prepared with a different core-coat ratio
gave better-sustained action. Eudragit RS100 and Eudragit RL100 gave sustained
action over 10 h and 4 h respectively. It was seen that the rate of drug
release from the microspheres depended on the polymer concentration of the
prepared devices. From Figure 3 and 4 it was observed that an inverse
relationship exists between polymer concentration and drug release rate from
the prepared microspheres. In all cases of polymers, it was seen that
microspheres containing 10% polymer released the drug more rapidly, while those
with 20% polymers exhibited a relatively slower drug release profile. Drug
release from Eudragit Rs100 microspheres was slow as compared to Eudragit RL100
microspheres this is due to the fact that Eudragit RL00 contains more
functional quaternary ammonium groups (10%) than Eudragit RS100 (5%) gives the
microspheres membrane a more open structure. Moreover, Eudragit RL100 is
strongly hydrophilic which causes easy diffusion of the dissolution medium and
hence good leaching of the drug. Due to strong permeability and greater
porosity of Eudragit RL100 the release of drug was more as compared to the
Eudragit RS100[16].
In case of effect of dispersing agent on drug release it was
seen that drug release decreases with increasing concentration of aluminium
tristearate at a constant polymer concentration. The decrease in drug release
is due to hydrophobicity of the dispersing agent. The increasing amount of
dispersing agent led to accumulation of free aluminium tristearate particles on
to the surfaces of microspheres.
In vitro dissolution
results showed that the RS2, RL6 microspheres gave better-sustained action up
to a period of 12 h. Hence these formulations were optimized and studied for
compatibility between drug and polymer.
Release Kinetics
From (Table 3) all the Eudragit
RS100 microspheres except RS1 and RS2 follows zero order kinetics (R2>0.9823) whereas the remaining
two gives best fit with Higuchi’s equation (R2>0.9919). Whereas for Eudragit
RL100 microspheres all the formulations showed best fit with zero order
kinetics (R2>0.9749)
The release mechanism of Ambroxol hydrochloride from various
formulations was determined by computing release exponent values ‘n’ from
Korsmeyer Peppas equation. From n value, RS1 microspheres showed Fickian
diffusion and remaining RS2 to RS9 anomalous type, which refers to a
combination of both diffusion and erosion controlled-drug release whereas RL1
to RL3 showed Fickian diffusion and RL4 to RL9 showed anomalous type. The
marketed preparation showed best fit with Higuchi’s equation (R2=0.9945) and exponent value of
0.54 indicating transport mechanism was anomalous type. The values of K showed
decreasing trend perceptible with increasing level of either polymer or
aluminium tristearate. It is already documented in literature that K is trait
function of polymer properties such as solubility, viscosity and molecular
weight [17].
Similarity factor (f2) and difference factor (f1) were calculated for optimized microspheres considering
marketed capsule as the reference standard. It was found that f1 and f2value for RS2 were 66.21 and
4.66 whereas for RL6, 64.56 and 4.50 respectively. This suggested that
microspheres RS2 and RL6 showed similarities of dissolution profiles with that
of marketed capsule (Figure 5)
t70%,of RS2, RL6 and marketed
capsule was 6.32h, 6.87h, and 6.34h respectively which suggested that
microspheres RS2, RL6 showed release profiles comparable with that of marketed
capsule.
Using two-way ANOVA statistically significant difference of both
the polymer on drug release, encapsulation efficiency and drug release was
found. (p=0.001-0.023). The effect of aluminium tristearate on the paricle
sizes obtained by both polymers was not found statistically significant. (p >0.05) but on encapsulation efficiency and drug release it was
significant. (p= 0.0014-0.020)
X-Ray Diffractometry (X-RD)
Characteristic crystalline peaks of Ambroxol hydrochloride were
observed at 2q of
12.13, 6.84, 5.64, 5.08, 4.34, 4.20, 3.94, 3.82, 3.71, 3.65, 3.31, 3.24, 3.16,
3.05, 2.95, 2.81, 2.62, 2.42 and 2.06 indicating the presence of crystalline
Ambroxol hydrochloride. Peaks of Ambroxol chloride are also present in RS2, RL6
microspheres even if reduced in intensity. This declination of drug
crystallinity reduces the intensity of peaks
[18]. Typical X-RD patterns of
Ambroxol hydrochloride loaded Eudragit RS100 and Eudragit RL100 microspheres
are shown in (Figure 6).
Differential Scanning Calorimetry
(DSC)
The characteristic endothermic peak for Ambroxol hydrochloride
was obtained at 243.0°C, which was also obtained in
RS2, RL6 microspheres with slender change. For RS2 it obtained at 238.5°C, for RL6 at 232.6°C, which showed, that drug is
dispersed in microspheres. Typical DSC patterns of Ambroxol hydrochloride
loaded Eudragit RS100 and Eudragit RL100 microspheres are shown in (Figure 7).
Fourier Infrared Spectroscopy
(FTIR)
The characteristic peaks of aromatic NH2, aliphatic NH,
aliphatic OH and aromatic C=C of pure drug were almost identical with those of
RS2, RL6 and EC2 microspheres which indicated that absence of any polymer drug
interaction. Typical FTIR patterns of Ambroxol hydrochloride loaded Eudragit
RS100 and Eudragit RL100 microspheres shown in (Figure 8).
Conclusion
In conclusion, the attempt to microencapsulate Ambroxol
hydrochloride was successful. The method showed good encapsulation efficiency
with high yield value. Aluminium tristearate and polymer concentration were
clearly effective on encapsulation efficiency, and in vitro drug release.
Particle size was affected by only polymer concentration not aluminium
tristearate. Due to low permeability Eudragit RS100 showed more encapsulation
efficiency and slow drug release as compared to Eudragit RL100.
Acknowledgments
The authors are grateful to Dr. D.V. Derle, Principal NDMVP’s
College of Pharmacy, Nashik for his valuable guidance and Glen mark
pharmaceuticals Ltd. Nasik for providing gift sample of Ambroxol hydrochloride.
Figure 1: Scanning
electron micrograph of Optimized RS2 microspheres at 1.00 KX.
Figure 2: Scanning electron
micrograph of optimizedRL6 microspheres at 1.00 KX magnifications.
Figure 3: In
vitro
dissolution profile of Ambroxol hydrochloride loaded Eudragit RS100
microspheres
Figure 4: In vitro dissolution
profile of Ambroxol hydrochloride loaded Eudragit RL100 microspheres
Figure 5: Comparativein vitro dissolution profile of optimized RS2 and
RL6 microspheres with marketed capsule M1
Figure 6: X-ray diffract
grams of Ambroxol hydrochloride (A), Eudragit RS100 (B), Eudragit RL100 (C),
Aluminium tristearate (D), RS100 microspheres (E), RL100 microspheres (F).
Figure 7: DSC curvesof
Ambroxol hydrochloride (A), EudragitRS100 (B), Eudragit RL100 (C), Aluminium
tristearate (D), RS100 microspheres (E), RL100 microspheres. (F)
Figure 8: FTIR spectra of
Ambroxol hydrochloride (A), EudragitRS100 (B), Eudragit RL100 (C), Aluminium
tristearate (D), RS100 microspheres (E), RL100 microspheres (F).
Batch code† |
Variable level
|
||
Polymer concentration (%)‡ |
Dispersing agent concentration (%)‡ |
||
RL1 |
RS1 |
10 |
3 |
RL2 |
RS2 |
15 |
3 |
RL3 |
RS3 |
20 |
3 |
RL4 |
RS4 |
10 |
2 |
RL5 |
RS5 |
15 |
2 |
RL6 |
RS6 |
20 |
2 |
RL7 |
RS7 |
10 |
1 |
RL8 |
RS8 |
15 |
1 |
RL9 |
RS9 |
20 |
1 |
|
† RS: EudragitRS100 and RL: Eudragit RL100 ‡ The concentrations of dispersing agents and polymer were calculated from dispersed inner phase volume (%w/v). Each formulation contained 1 g of Ambroxol HCl.
|
Table 1: Formulations of Ambroxol Hydrochloride Microspheres
Batch code
|
YV (%) |
EE (%) |
d † |
SPAN |
RS1 |
82.26 |
82.862±0.548 |
27.67±0.127 |
1.373 |
RS2 |
92.24 |
83.461±0.403 |
26.62±0.204 |
1.555 |
RS3 |
83.55 |
86.427±1.236 |
30.48±0.089 |
1.525 |
RS4 |
87.96 |
89.758±0.619 |
38.11±0.094 |
1.246 |
RS5 |
85.72 |
90.982±0.645 |
29.32±0.249 |
1.588 |
RS6 |
92.89 |
91.407±0.528 |
32.46±0.042 |
1.642 |
RS7 |
96.25 |
92.625±0.765 |
43.01±0.346 |
1.424 |
RS8 |
90.59 |
93.827±1.380 |
35.63±0.076 |
1.566 |
RS9 |
85.03 |
95.424±0.636 |
38.33±0.418 |
1.282 |
RL1 |
86.66 |
76.16±0.509 |
28.79±0.035 |
1.518 |
RL2 |
85.00 |
78.72±0.858 |
23.08±0.287 |
1.350 |
RL3 |
84.52 |
81.75±0.502 |
32.50±0.548 |
1.498 |
RL4 |
86.91 |
82.31±0.657 |
39.20±0.426 |
1.431 |
RL5 |
98.96 |
86.70±0.799 |
29.48±0.054 |
1.324 |
RL6 |
97.4 |
88.26±0.758 |
31.84±0.016 |
1.598 |
RL7 |
89.35 |
91.42±.009 |
40.34±0.388 |
1.337 |
RL8 |
74.43 |
92.56±0.825 |
32.96±0.064 |
1.495 |
RL9 |
85.60 |
93.60±0.848 |
44.18±0.092 |
1.447 |
* YV indicates yield value; EE, encapsulation efficiency (n=3) † Values shown represent the equivalent volume diameter (µm). (n=3)
|
Table 2: Physical Properties of Microspheres.
Kinetic models
|
|||||
Batch code |
Zero order |
Higuchi model |
Peppas model |
||
R2 |
K0 (%mg/h) |
R2 |
Kh (%mg/h1/2) |
n |
|
RS1 |
0.986 |
5.838 |
0.9974 |
31.793 |
0.3847 |
RS2 |
0.9882 |
5.961 |
0.9919 |
28.942 |
0.5278 |
RS3 |
0.9974 |
5.931 |
0.9828 |
27.325 |
0.5991 |
RS4 |
0.9823 |
5.142 |
0.9281 |
23.324 |
0.6431 |
RS5 |
0.9962 |
4.470 |
0.9561 |
20.882 |
0.5828 |
RS6 |
0.9971 |
3.936 |
0.9629 |
17.981 |
0.6084 |
RS7 |
0.9976 |
3.991 |
0.9722 |
16.985 |
0.7297 |
RS8 |
0.9987 |
3.246 |
0.967 |
13.452 |
0.7654 |
RS9 |
0.9899 |
3.070 |
0.9387 |
11.298 |
0.803 |
RL1 |
0.9749 |
10.135 |
0.9362 |
48.755 |
0.3812 |
RL2 |
0.9836 |
9.192 |
0.9677 |
43.688 |
0.4068 |
RL3 |
0.9909 |
7.868 |
0.9868 |
36.840 |
0.4433 |
RL4 |
0.9981 |
6.830 |
0.985 |
33.290 |
0.4586 |
RL5 |
0.9993 |
6.701 |
0.9774 |
31.569 |
0.5051 |
RL6 |
0.9901 |
5.732 |
0.9873 |
29.003 |
0.4743 |
RL7 |
0.9933 |
5.575 |
0.981 |
26.881 |
0.5675 |
RL8 |
0.9961 |
5.170 |
0.9747 |
23.503 |
0.6176 |
RL9 |
0.9962 |
4.674 |
0.9578 |
20.799 |
0.6384 |
Table 3: In vitro Release Kinetic Parameters of Ambroxol Hydrochloride Loaded Eudragit Microspheres.
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