Floating micro particles of Stavudine: An Exceptional approach for Gastric retention and Sustainable drug action
Ande Hemanth Kumar, Preethi Sudheer*, Ashwini M.
Dept. of Pharmaceutics, Krupanidhi College of Pharmacy, #12/1, Chikkabellandur,
Carmelram Post, Bangalore, 560035, Karnataka, India.
*Corresponding Author E-mail: preetisudheer@gmail.com
ABSTRACT:
Stavudine is synthetic analog of reverse transcriptase inhibitor possessing a short half-life of 0.8 to 1.5 hours. Therefore frequent administration of the medication is required which results in poor patient acceptability The following research work aims to prepare the floating microparticles of stavudine with an intention to increase the gastric retention time. Microparticles were prepared via emulsion solvent diffusion method utilizing Eudragit S 100 and Eudragit L 100 as the rate controlling polymers. The influence of these polymers and its compositions on various formulation parameters in addition to the in vitro release characteristics of the microspheres was investigated. The particle size of the prepared microparticles were found to be in the range of 108.25µm to 152.41µm. Free flowing particles which are spherical free flowing with a buoyancy ≥12 hour in the simulated gastric fluid were obtained. The drug content of the selected micro particles (F12) showed an encapsulation efficiency of up to 85.28±0.18%. In vitro release profiles of floating microspheres indicated a sustained drug release up to 14 hours. Thus, the present formulations could be a superior alternative to conventional oral therapy due to the sustained drug action.
KEYWORDS: Eudragit, Buoyancy, In vitro release, kinetics, Stavudine.
INTRODUCTION:
Various approaches prolongs the gastric retention include floating drug delivery systems, swelling and expanding systems, polymeric bioadhesive systems, modified-shape systems, high density systems and other delayed gastric emptying devices etc4,5. Gastric floating drug delivery systems (GFDDS) remain buoyant in the virtue of its low bulk density6.
Floating microparticles are spherical or irregular shaped particles without a core. In the process of buoyancy over gastric contents, the drug release is controlled at a desired rate, thus prolongs the gastric retention. This can avoid fluctuations in plasma drug concentration, there by greater safety of the drug therapy is assured.7
In the present investigation, Stavudine has been selected as model candidate for the formulation of GFDDS. Stavudine is one of the commonly prescribed antiviral drug which comes under nucleoside reverse transcriptase inhibitor category. Stavudine has short biological half-life of 0.5- 1.5 hours that necessitates it to be administered in 2 or 3 doses of 40mg per day8 To overcome these drawbacks, the present study is focused on the formulation of floating microparticles with prolonged gastric retentive behavior.
MATERIAL AND METHODS:
Preparation of microparticles:
Floating microparticles were prepared by emulsion solvent diffusion method. Weighed amount of drug was dissolved in a solvent system of ethanol: dichloromethane (1:1) at room temperature. The aqueous phase consisted of 200ml of aqueous solution of 0.75% w/v polyvinyl alcohol, maintained at constant temperature of 400C. The polymer solution was added to aqueous under magnetic stirring at a speed of 300rpm for 1 hour. The microparticles then obtained was filtered, washed with water and dried overnight at 400C9. The formulation chart is given in table 1.
Table: 1 Formulation chart
|
Formula |
Drug (mg) |
Eudragit S (mg) |
Eudragit L(mg) |
Eudragit S and Eudragit L(mg) |
Ethanol: DCM |
PVA (%w/v) |
|
F1 |
250 |
250 |
- |
- |
1:1 |
0.75 |
|
F2 |
250 |
500 |
- |
- |
1:1 |
0.75 |
|
F3 |
250 |
750 |
- |
- |
1:1 |
0.75 |
|
F4 |
250 |
1000 |
- |
- |
1:1 |
0.75 |
|
F5 |
250 |
- |
250 |
- |
1:1 |
0.75 |
|
F6 |
250 |
- |
500 |
- |
1:1 |
0.75 |
|
F7 |
250 |
- |
750 |
- |
1:1 |
0.75 |
|
F8 |
250 |
- |
1000 |
- |
1:1 |
0.75 |
|
F9 |
250 |
- |
- |
250 |
1:1 |
0.75 |
|
F10 |
250 |
- |
- |
500 |
1:1 |
0.75 |
|
F11 |
250 |
- |
- |
750 |
1:1 |
0.75 |
|
F12 |
250 |
- |
- |
1000 |
1:1 |
0.75 |
Evaluation of microparticles:
Particle size analysis:
By the use of an optical microspore, 100 microparticles were counted. After spreading the microparticles uniformly on a slide, diameter was measured along the longest axis and the shortest axis (cross shaped measurement) and the average of these two readings is taken as diameter.10
Surface electron microscopy:
The surface morphology was studied using surface electron microscope, model JSM 6100 JEOL at 20 kV. After gold-sputtering photo, graphs were scanned under the microscope10.
Determination of percentage yield:
After collecting the microparticles, the ‘percentage yield was calculated by the following formula
Weight of microparticle
Yield (%) ------------------------------------------------------------ x 100
Total expected weight of drug and polymer
Bulk Density:
Bulk density was determined by calculating by the volume occupied by a known amount of microparticles in a graduated cylinder and is calculated using the following formula.
Weight of microparticle
Bulk density = ------------------------------
Bulk Volume
Compressibility index (Carr’s index) and Hausner Ratio:
The compression nature and the flow behavior of microparticles were determined by Carr’s index and Hausner ratio respectively from the following formulas.
Tapped density – Bulk Density
Carrs Index = ------------------------------------------ x 100
Tapped density
Tapped density
Hausner ratio = ------------------------ x 100
Bulk Density
Angle of repose (θ):
The smooth surface behavior of microparticles were assessed by angle of repose. The height (h) and radius(r) of the heap were measured after passing a known weight of microparticles from funnel with a circular base to a flat surface. The angle of repose was calculated using the formula11.
Angle of repose (θ) = tan-1 (h/r)
Determination of drug content and entrapment efficiency:
A known amount of microparticles was digested with 50 ml of 0.1N HCl, and filtered. The filtrate was suitably diluted with 0.1N HCl and absorbance was measured at 266 nm using spectrophotometer (UV 1700, Shimadzu, Japan) at 266 nm against 0.1N HCl as blank. The entrapment efficiency is given by11.
Initial weight of drug – weight of free drug
Drug entrapment (%)= -------------------------------------------------- x 100
Initial weight of drug
Floating behavior (%buoyancy):
About 50 mg of the microparticles were placed in 100 ml of simulated gastric fluid (0.1N HCl), under magnetic stirring for 14 hours. The buoyant microparticles was separated by filtration and dried. Buoyancy (%) was calculated by the following formula12.
Weight of floating microparticles after time
Buoyancy (%) = --------------------------------------------------------- x100
Initial weight of microparticles
Differential scanning calorimetry (DSC):
The drug excipient interactions were determined by differential scanning calorimeter; MDSC 2920 Mettler-Toledo, USA DSC. Both pure drug and micro particles (1 to 5mg) was packed in aluminum lid which in turn was placed in the sample cell and an empty pan was used as reference. Thermogrmas were recorded at a temperature of 0°C - 300°C under a heating rate of 5°C /minute under nitrogen flow of 50ml/minute13.
In vitro drug release studies:
The microparticles loaded on to metallic mesh, was placed into the basket assembly of USP type I apparatus. The drug release studies were carried out in 900ml 0.1N HCl at 37°C and at an rpm of 100. At specific time intervals, 1ml aliquots were withdrawn, replaced with fresh buffer and analyzed UV spectrophotometrically at the λ max of 266nm after suitable dilution against blank 0.1N HCl.14.
Release kinetics:
The results of in vitro release profiles obtained for the best formulation was fitted into various kinetic models to understand the release mechanism zero, first-order kinetic model, Higuchi’s model and Korsmeyer-Peppas equation.15
RESULTS AND DISCUSSION:
Particle size:
The mean particle size was diverse due to variation in the polymer blend used for the preparation of microparticles.
The size of micro particles was found to be proportionately increased with the increase in the polymer concentration. The results shown in the table 2. This result might be attributed to the fact that higher polymer concentration lead to an increase in the in the viscosity of the polymer phase. Thus an augmented interfacial tension brought about the coagulation of droplets of emulsified phase. The particle size was in the ranged between 108.25±3.21 to 152.41±2.31μm.
Flow behavior of microparticles:
The microparticles were evaluated for bulk density, Carr’s index, Hausner’s ratio and angle of repose. Carr’s index of anywhere less than 15% indicates excellent flow behavior and good compaction properties. This is again substantiated by angle of repose less than 300. The results indicated an excellent flow behavior of the microparticles in comparison to the neat sample. This improvement in flow properties suggested its handling ability, packing properties; there by it may ease the encapsulation process and ease of compression; thus improved tablettability in comparison to pure drug crystals.
Table 2: Data for characterization of stavudine floating microparticles
|
Product code |
Mean particle size(μm) |
Bulk Density(gm/ml) |
Carr’s Index |
Hausner’s ratio |
Angle of repose(θ) |
|
F1 |
108.25±3.21 |
0.166±0.01 |
3.48±0.13 |
1.03±0.06 |
24.25±0.51 |
|
F2 |
115.31±2.56 |
0.201±0.03 |
7.37±0.16 |
1.07±0.03 |
25.54±0.32 |
|
F3 |
124.44±2.23 |
0.216±0.01 |
4.84±0.18 |
1.05±0.04 |
26.95±0.62 |
|
F4 |
136.35±4.19 |
0.250±0.02 |
4.94±0.22 |
1.05±0.02 |
26.23±0.21 |
|
F5 |
112.11±1.15 |
0.202±0.04 |
9.00±0.13 |
1.09±0.04 |
26.95±0.55 |
|
F6 |
118.13±1.16 |
0.208±0.02 |
5.02±0.14 |
1.05±0.02 |
25.91±0.68 |
|
F7 |
142.15±1.58 |
0.216±0.03 |
1.81±0.21 |
1.01±0.08 |
25.25±0.85 |
|
F8 |
151.19±1.92 |
0.225±0.05 |
1.31±0.21 |
1.01±0.07 |
24.35±0.62 |
|
F9 |
138.25±1.54 |
0.233±0.01 |
2.10±0.14 |
1.02±0.05 |
26.95±0.57 |
|
F10 |
141.33±1.26 |
0.241±0.02 |
2.42±0.12 |
1.02±0.04 |
28.50±0.26 |
|
F11 |
152.41±2.31 |
0.252±0.03 |
4.18±0.31 |
1.01±0.02 |
27.70±0.61 |
|
F12 |
148.27±2.36 |
0.266±0.03 |
3.97±0.25 |
1.04±0.04 |
27.31±0.35 |
Drug entrapment efficiency:
Entrapment efficiency is an important parameter which suggests the suitability of the process employed, processing conditions and concentration of the agents used in the preparation of microparticles. As shown in the figure1, loading efficiency for the microparticles was in the range of 55.25±0.81% to 85.28±0.18%. It was also observed that microparticles prepared by combination of both polymers was much higher values in comparison product prepared from individual polymers. (Fig 3)
The surface morphology:
The surface morphology and shape of stavudine loaded floating microparticles by SEM analysis revealed discrete spherical nature of the microparticles as given in fig. 1.
Figure: 1 Scanning electron micrograph of F4 and F12
Buoyancy:
In vitro floating efficiency of the microparticles are expressed as percentage buoyancy. The percentage buoyancy ranged from 68.25±1.3% to 81.28±3.1%. The results indicated that the microspheres prepared with the combination of Eudragit S and Eudragit L showed a higher buoyancy, this can be attributed to the synergistic action of the combination of polymers on the swelling property. The figure 2 represents buoncy test and figure 3 represents percentage bouncy.
Figure: 2. Buoyancy test
Figure: 3. Evaluation of microparticles
Differential scanning calorimetry (DSC):
Thermograms of pure drug exhibited a sharp endothermic peak was observed at 172oC and also it is observed that there was slight shift in the similar endothermic peak to 170oC. This confirms that there was no drug polymer interaction. The results are given in the figure 4.
Figure: 4 DSC thermogram of (a) Pure stavudine (b) F12 formula
In vitro drug release and kinetics of drug release:
In vitro drug release was carried out to compare the release rate from the formulation prepared using different ratio of polymers. The cumulative amount of stavudine released as a function of time from different formulations is depicted in figure 5. An extended drug release was observed from all most all formulations for up to 14 h. The results indicated that formulation prepared from the blend of Eudragit S and Eudragit L showed superior release characteristics. Maximum release up to 91.13±0.16% was seen with F12 formulation. To understand the mechanism of drug release from microparticles, the in vitro release data obtained for F12 were fitted to various kinetic models including zero order, first order, Higuchi and Korsmeyer-Peppas release models. The zero order plots were found to be fairly linear as indicated by high regression value of 0.978 for F12. The n value 1.0012 obtained from the Korsmeyer-Peppas model showed that the formulation F12 followed the super case-II transport, which indicated that drug release from floating microparticles by diffusion controlled polymeric relaxation.
Figure: 5 Cumulative percentage drug release profile from Stavudine floating microparticles F1-F4, F5-F8, F9-F12
CONCLUSION:
Novel floating Stavudine loaded floating microparticles were successfully prepared by solvent evaporation method using the polymers Eudragit S 100, Eudragit L 100 and Combination of these two. The low density of the microparticles can be attributed for their good floating ability which is evident from the percentage buoyancy. In-vitro drug release studies, showed that by changing the ratio of polymer, drug release can be controlled.
Drug release kinetics performed for the ideal formulations, fitted best with zero order and a Korsemeyer peppas release mechanism. Based on the above observations, it could be concluded that the formulated floating microparticles of stavudine with combination of polymer Eudragit S 100, Eudragit L 100 can be accepted and considered physiologically safe and capable of exhibiting controlled release properties over period of 14 hours. They may be beneficial in minimizing the occurrence of side effects, by decreasing the frequency of dosing and increasing the residence time in stomach thus increasing the therapeutic effectiveness of the Stavudine.
ACKNOWLEDGMENT:
Authors thank management, Krupanidhi college of Pharmacy for their encouragement and support.
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Received on 16.01.2020 Modified on 01.04.2020
Accepted on 04.05.2020 © RJPT All right reserved
Research J. Pharm. and Tech. 2021; 14(7):3816-3820.
DOI: 10.52711/0974-360X.2021.00661