FORMULATION AND IN-VITRO EVALUATION OF FLOATING MICROBALLOONS OF STAVUDINE

Felix Sunday Yusuf

Contec Global Agro Limited, Abuja, Nigeria.

                       Corresponding author:  Email: Phelixsunday@yahoo.com

   DOI: http://doi.org/10.22270/ujpr.v1i1.R3

ABSTRACT

Objective of present study involves preparation and evaluation of floating microballoons of Stavudine. It is a potent antiviral agent, used for treatment of human immunodeficiency virus (HIV) infection. In present study Stavudine is used as a model drug, to increase its residence time in the stomach without contact with the mucosa. The microballoons were prepared by the emulsion solvent diffusion technique using different ratio of polymers (Eudragit S100, Ethyl cellulose and PVP K 30) as carriers. The yield of microballoons was up to 68.32-80.22%. The cumulative percent drug release after 24 hrs of the Stavudine microballoons was in the range of 53.62 to 87.45%. 

Keywords: Emulsion solvent diffusion method, floating drug delivery system, floating microballoons, Stavudine.

INTRODUCTION

The main purpose of any drug delivery system is effective control of disease, minimum side effects and better patient compliance in the cost effective way¹.

Dosage forms retained in the stomach are called gastro retentive drug delivery systems.

Gastroretentive drug delivery is an approach to prolong gastric residence time, thus targeting site-specific drug release in the upper gastrointestinal tract for local or systemic effects. Gastroretentive dosage forms can remain in the gastric region for long periods and hence prolong the gastric retention time of drugs².

Floating drug delivery systems have a bulk density lower than gastric fluids and thus remain buoyant in stomach for a prolonged period of time, without affecting the gastric emptying rate³.

Microballons, refer to hollow microsphere in gastro-retentive drug delivery based non-effervescent approach. They are spherical empty particles without core made up of synthetic polymers or natural proteins, ideally having a size less than 200μm. They float immediately upon contact with gastric fluid and gives promising approaches for increasing the bioavailability of drugs with absorption windows in upper small intestine and stomach⁴.

Stavudine is a potent antiviral agent belongs to the class of nucleoside reverse transcriptase inhibitors. It is used along with other drugs for treatment of human immunodeficiency virus (HIV) infection. It decreases the amount of HIV in blood⁵.

While Stavudine administered orally as a capsule and an oral solution, it has a very short half-life (1.30hrs).

Thus there is need of frequent administration of large doses of it to maintain therapeutic concentration^6,7.

Moreover use of Stavudine is associated with many limitations such as adverse effects due to accumulation of drug during multi dose therapy, poor patient compliance, and high cost^8,9.

The objective of the present study was to prepare floating microballoons of Stavudine to overcome these problems and to increase its gastric residence time in the stomach, consequently enhance its bioavailability and increase patient compliance.

MATERIALS AND METHODS

Stavudine was received as gift sample from ASPEN Pharmacare NIG. LTD, Eudragit S 100 from BOLAR Pharmaceuticals Ltd, and EC from Drugfield Pharmaceuticals Ltd, Nigeria. All other chemicals were of analytical grade.

DEVELOPMENT OF FLOATING MICROBALLOONS

Stavudine floating microballoons were prepared by emulsion solvent diffusion method¹⁰. 200 mg Stavudine and polymers in different ratio were mixed in ethanol by using blending solvent dichloromethane and heavy liquid paraffin. The slurry was introduced into 250ml beaker containing 0.2% Tween 80. The stirring was done

for 2hrs at 1000-1200 rpm by mechanical stirrer equipped with four bladed propellers, to evaporate the volatile solvent. After evaporation of solvent, microballoons were collected by filtration, washed with water and dried at room temperature in a desiccator for 24 h.

EVALUATION PARAMETERS

1. % Yield of microballoons: Percentage yield of microballoons was calculated using the following formula¹¹.
2. Microballoons size: The size was measured using an optical microscope and the mean microballoons diameter was calculated by measuring 100 particles with the help of a calibrated ocular micrometer¹².
3. Sphericity of the microballoons

Sphericity, of prepared microballoons were taken on a black paper using camera lucida¹³.

Circulatory factor (S) was calculated using,

Where A is area (cm²) and, P is the perimeter of the circular tracing

4. Drug entrapment efficiency

Accurately weighed 10 mg of crushed microballoons were dissolved in 0.1N HCl, and then transferred to 100 ml volumetric flask. The volume was made up to 100 mL with 0.1N HCl. The solution was filtered using Whatman filter paper no. 41. The samples were assayed for drug content using UV spectrophotometry at 265nm¹³.

The amount of drug entrapped in the microballoons was calculated by the following formulae:

5. Assessment of in-vitro buoyancy

The floating microballoons about 100 mg were spread over the surface of the dissolution medium of 900 ml simulated gastric fluid (SGF, pH 2.0), which is placed in USP dissolution apparatus II.

The medium temperature was maintained at 37°C and was agitated by paddle at 100 rpm¹⁵. After agitation the microballoons that floated over the surface of the medium and those that settled down at bottom of the flask were recovered separately and dried. The percentage of floating microballoons was determined by the following equation: 

Where WF  and WS are the weight of floating and settled microballoons respectively.

6. In-vitro drug release studies

The in-vitro dissolution studies were carried out by using USP II paddle type dissolution apparatus. Accurately 100 mg of  microballoons was introduced into 900 ml of 0.1 N HCl (pH 2), used as a dissolution medium, maintained at a temperature of 37°C, and a rotational speed of 100 rpm. Samples were withdrawn at predetermined time intervals of every one hour for twelve hours. The samples were analyzed UV spectrophotometrically at 265 nm to determine the percentage of drug release¹⁶.

RESULTS AND DISCUSSION

Eight floating microballoons formulations of Stavudine were prepared by using different polymers i.e. Eudragit S100, EC and PVP K30, in different ratio

by emulsion solvent diffusion method.

The mean particle diameter of the microballoons was between 230.23-238.33µm. In general as the polymer concentration increases, the particle size also increases. This is because the viscosity of the polymer solution increases with increasing polymer concentration, which in turn decreases the stirring efficiency. The sphericity factor obtained for the microballoons lies in the range of 1.04-1.14. The sphericity value nearer to 1 indicates that the prepared formulations were spherical in nature.

High incorporation efficiencies are seen with lower concentrations of polymer with the drug.  The percentage entrapment efficiency of the microballoons was between 74.64-85.37%.  

The percentage yield of the microballoons was between 68.32-80.22%.      

The purpose of preparing floating microballoons was to extend the gastric residence time of a drug.

The floating ability test was carried out to investigate the floatability of the prepared microballoons. The mean percentage buoyancy of the microballoons was between 69.23-82.53%. In-vitro buoyancy studies reveal that in spite of stirring the dissolution medium for more than 12 hrs formulations were still continued to float without any apparent gelation, thus indicating that microballoons exhibit excellent buoyancies which can be attributed to the pores and cavities present in them.

 In general with increase in the amount of polymers there is an increase in the buoyancy percentage. The increase in the buoyancy percentage may be attributed to air which caused swelling because of increased amount of the polymers present. The good buoyancy behavior of the microballoons may be attributed to the hollow nature of the microballoons.

The cumulative percent drug release after 24 hrs of the Stavudine microballoons was 53.62 to 87.45%.  Maximum percent release was shown by formulation containing Eudragit S 100 and Ethylcellulose of batch MB4. It was also observed that the drug release generally decreased as the polymer ratio increased. The release of the drug was retarded due to the hydrophobic and insoluble nature of the polymers used.  The increased density of the polymer matrix at higher concentrations results in an increased diffusion path length. This may decrease the overall drug release from the polymer matrix. Furthermore, smaller microballoons are formed at a lower polymer concentration and have a larger surface area exposed to dissolution medium, giving rise to faster drug release.

Statistical analysis

Experimental results were expressed as mean±SD. Student’s t-test and one-way analysis of variance (ANOVA) were applied to check significant differences in drug release from different formulations. Differences were considered to be statistically significant at p < 0.05.

CONCLUSION

In present study 8 different Stavudine floating microballoons formulations were prepared with a view of improving its oral bioavailability and giving a prolonged release of drug. The microballoons show satisfactory yield and impressive drug entrapment efficiency. Release properties were satisfactory and the formulations  hold promise for further development into drug delivery systems for oral administration of Stavudine.

In vitro drug release studies showed that the drug release was more in case of formulations MB4. Stavudine floating microballoons formulations of batch MB4 was concluded as the optimum formulations among the all 8 formulations based on different parameters. However there is need of in-vivo study to justify the development of Stavudine floating microballoons.

CONFLICT OF INTEREST

No conflict of interest was associated with this work.

REFERENCES

1. Moes AJ. Floating delivery and other potential gastric retaining systems. Current Status on Targeted Drug Delivery to the Gastrointestinal Tract , Capsugel Symposia Series. 1993; 97-112.
2. Sahoo SK, Mallick AA, Barik BB, Senapati PC. Formulation and in vitro evaluation of eudragit microspheres of stavudine. Trop J Pharm Res. 2005; 4: 369–375.
3. Kawashima Y, Niwa T, Takeuchi H, Hino T, Ito Y. Preparation of multiple unit hollow microspheres (microballoons) with acrylic resins containing tranilast and their drug release characteristics (in vivo). J Control Release. 1991; 16:279–90.
4. Behera BC, Sahoo SK, Dhal S, Barik BB, Gupta BK. Characterization of glipizide-loaded polymethacrylate microspheres prepared by an emulsion solvent evaporation method. Trop J Pharm Res. 2008; 7: 879–885.
5. Potnuru S, Sundaramoorthy K, Vetrichel Van T, Design of biodegradable polymer nanoparticles for oral drug delivery of stavudine: in-vitro dissolution studies and characterization. Int J Pharm T. 2010; 3(1): 1360-1372.
6. Yasmin Begum M, Sankar Dasari, M Sudhakar, BVS Lakshmi, K Manga. Development and evaluation of co-encapsulated Stavudine and Lamuvudine niosomes for the controlled delivery. Der Pharmacia Sinica. 2012; 5(1):1-10.
7. Wangsomboonsiri W, Mahasirimongkol S. Association between HLA-B4001 and lipodystrophy among HIV-infected patients from Thailand who received a stavudine-containing antiretroviral regimen. Clinical infectious diseases. 2010; 50 (4): 597–604.
8. Horwitz JP, J Chua, DaRooge M. Nucleosides. IX. The formation of 2, 3′-unsaturated pyrimidine nucleosides via a novel β-elimination reaction. J Org Chem. 1996; 31: 205.
9. Yuasa H, Takashima Y, Kanaya Y. Studies on the development of intragastric floating and SR preparation application of calcium silicate as a floating carrier, Chem Pharm.1996; 44:1361-1366.
10. Singh Bandana, Kanoujia Jovita, Pandey Manisha, Saraf Shubhini, Formulation and Evaluation of Floating Microspheres of Famotidine. Int J of Pharm Tech Research. 2010; 2(2), 1415-1420
11. Singh Bandana, Kanoujia Jovita, Pandey Manisha, Saraf Shubhini, Formulation and Evaluation of Floating Microspheres of Famotidine. Int J of PharmTech Research. 2010; 2(2), 1415-1420
12. Singh B, Kanoujia J, Pandey M, Saraf S. Formulation and evaluation of floating microspheres of famotidine. Int J of PharmTech Research. 2010; 2(2), 1415-1420
13. Venkatesh G, Srinivasa M, Kiran Kumar. Radhika PDL. Formulation and in-vitro Evaluation of mucoadhesive microspheres loaded with stavudine using hydrophilic macromolecular polymers. Research J Pharm Dos techn. 2014; 6(2), 99-104.
14. Venkatesh G, Ganesh NS. Formulation and evaluation of mucoadhesive microspheres macromolecular polymers using Flurbiprofen as model drug” Der pharmacia Lettre. 2012; 4(5): 1560-1566.
15. Kulkarni RV, Sreedhar V, Mutalik S, Setty CM. Interpenetrating network hydrogel membranes of sodium alginate and poly(vinyl alcohol) for controlled release of prazosin hydrochloride through skin. Int J Biol. Macromol. 2010; 47, 520–527.

16. Sato Y, Kawashima Y, Takeuchi H, Yamamoto H. In vivo evaluation of riboflavin containing microballons for floating controlled drug delivery system in healthy human volunteers. J Control Release. 2003; 93:39-47.

Table 1: Composition of floating microballoons formulations of Stavudine

Table 2: Characterization of floating microballoons formulations of Stavudine 

Figure 1:  Percentage drug released from microballoons of batch MB1 to MB4

Figure 2:  Percentage drug released from microballoons of batch MB5 to MB8