Formulation and Evaluation of Acyclovir Sodium Solid Lipid Microparticles

Acyclovir sodium is an antiviral drug used to treat herpes, chicken pox and herpes skin infections. Acyclovir sodium potential as an antiviral drug is limited by its low oral bioavailability (20-30%) with short half-life (2-3 hours) with poor plasma protein binding. There is an opportunity to utilize Acyclovir sodium as an antiviral drug by enhancing the bioavailability by formulation technology. In this paper solid microparticle (o/w) of Acyclovir was prepared by melt dispersion technique. The characterization of drug using scanning electron microscopy, FT-IR, particle size, percentage yield, drug loading capacity, hausner’s ratio and carr’s index, bulk density and tapped density. In vitro drug release studies using phosphate buffer has shown as formulation F5 sustained release for 17 hrs.


INTRODUCTION
Acyclovir is an antiviral drug which slows the spread and growth of herpes virus. It is also used to treat genital herpes, cold sores, shingles and chicken pox. Acyclovir has a low bioavailability of 20-30% and excreted in unchanged in urine both by filtration and secretion. Hence it is prescribed 3-4 times a day which has negative effect on patient compliance 1 . Acyclovir may also cause side effects like bleeding, purple or red pinpoint spots under skin, no urinating , painful or difficult urination, swelling in feet or ankles, feeling tired or short of breath. In order to enhance the efficacy and to improve safety formulation of solid lipid micro particles is carried out. Solid lipid micro particles are having size between in the range of 1-1000 μm with drug being dissolved, entrapped and encapsulated in micro particle matrix 2 .
The drug entrapment got upto 80% which are easily compatible with living systems since SLMs system based of biomaterials. In SLMs drug is protected from degradation as it is sealed in the biomaterial matrix. The leaching of the drug is passive mechanism and is independent of concentration of drug. As the micro particle continues get dissolved leading to slow sustained release of the drug in the stomach. The suitability of solid lipid micro particles for sustained release has been established by several authors [3][4][5] . SLMs can be prepared by Spray-drying, Spray congealing, O/W melt dispersion technique, Double-emulsion solvent evaporation, solvent evaporation, High pressure homogenization, w/o melt dispersion technique 6 . The improvement in patient can be dosing schedule can be reduced one or two times. In this paper SLMs of Acyclovir sodium of different concentrations of bio lipids are prepared using stearic acid by o/w melt dispersion techniques. The various formulations are evaluated for suitability of formulation of sustained released preparation 7 .

Material
All the reagents and chemical used are of analytical grade doubly distilled water was used in making preparation in this study. Acyclovir sodium (Helix Pharma Pondicherry, India), Stearic acid (Lipidchem Johor, Malaysia), Tween 80 (Thomas baker Mumbai, India), Dimethyl sulfoxide (SD fine chemicals, Mumbai, India).

Preparation of Solid Lipid Micro Particles containing Acyclovir Sodium
Two different methods were used for preparation of solid lipid micro particles with Dimethyl sulfoxide.

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In method 1 SLMs were prepared in o/w melt preparation technique. Stearic acid was melted on a water bath with a temperature limit of 72°C. The drug particles grounded to the fine size was dispersed with molten stearic acid aqueous phase consisting of water and tween 80 at 72°C was the molten phase was slowly added to the aqueous phase by steering and the emulsification was assisted by homogenizer for 15 minutes 8 . The dispersion rapidly cools down at 20°C by immersing the solution in ice bath. The formed micro particles were separated by the filtration by this formulation F1, F2, F3 and F4 were prepared. In another method formulation F7 and F8 were prepared by same method. However the Dimethyl sulfoxide is used instead of water and tween 80 to dissolve finally grounded acyclovir sodium ( Table 1).

Characterization of SLMs of Acyclovir Sodium:
The characterization of Acyclovir was carried out using FT-IR spectrum and Scanning Electron Microscopy 10 .

FT-IR spectrum:
The KBr disc technique was employed for preparation of sample. Pellet of 1 mg Acyclovir sodium and 100 mg dried spectroscopic grade KBr was prepared in a die with the application of pressure and pellet was analyzed using FT-IR Spectrophotometer.
Scanning electron microscopy: Scanning electron microscopy (SEM) was used to verify uniformity of particle shape and size. The samples were previously fixed on a brass stub using double-sided adhesive tape and were then made electrically conductive by coating with a thin layer of gold and palladium alloy (180-200Å) using a fine coat ion sputter (SUK PHY) (JEOL, fine coat ion sputter JFC-1100). The surface morphology of the sample was observed under a scanning electron microscope JSM-6400 (Joel, Japan) operated at 10kev pulse at different resolutions 11 .
Evaluation of SLMs Particle size: The particle sizes of the microparticles were determined by using optical microscopy method. Approximately 100 microparticles were counted for particle size analysis by using calibrated optical microscope 12

Percentage (%) yield and drug loading capacity:
The prepared microparticles were collected and weighed. The measured weight was divided by the total weight of all the excipients and drug. To calculate the drug loading capacity, weighed 10 mg drug was added to 10 ml of phosphate buffer (pH 6.8) to facilitate the microparticles to get dissolved and heated at 70°C,then the resultant solution centrifuged at 8000 rpm for 10 min. Samples were measured at an absorbance of 252 nm in double beam U.V Spectrophotometer. Percentage yield and drug loading capacity of microparticles were determined by the following equations:

In Vitro Dissolution Studies
In vitro drug release study was carried out using USP Dissolution apparatus (Type II). The formulations equivalent to weight containing 200 mg acyclovir sodium were immersed in dissolution medium. Phosphate buffer (pH 6.8) (900 ml) was used as the dissolution medium and maintained at 37 ± 0.5°C at a rotation speed of 50 rpm. Samples were withdrawn and the same amount was replaced using the same dissolution medium. The amount of the drug was quantified using double beam U.V spectrophotometer at 252 nm 14 .

Drug Release Kinetic Studies
Raw data obtained from in vitro release studies was analyzed,and it was fitted to different equations and kinetics model to calculate the percent drug release and release kinetics of acyclovir sodium from microparticles. The kinetic models used were zero-order equation, first-order, higuchi's model and korsmeyerpeppas equation 15 . for Acyclovir sodium showed in Figure 1. So presence of these characteristic peaks of Acyclovir sodium in physical mixture reveals that the drug remains intact in formulation F5 and there is no interaction between drug and stearic acid used Figure 2.

Characterization and Evaluation of SLMs
Scanning electron microscopy: Scanning electron microscopy was performed for lipid microparticles of formulation F5 to obtain more information on the particle size and morphology.
The photos of lipid microparticles shows that the formulated acyclovir sodium microparticles were of spherical shape, which were shown in Figure 3. Moreover the microparticles were observed with smooth surface, which may contribute to its release of the drug in a sustained manner compared to the microparticles having rough surface.

Evaluation of SLMs
Particle size, percentage yield and drug loading capacity: The reason behind selecting solid lipid microparticles was their ability to have better particle size (7 µm), percentage yield and to better drug entrapment. Drug loading capacity is considered as an important parameter as improper entrapment leads to the initial burst release of the drug, which hinders its sustained release property. Acyclovir sodium solid lipid microparticles of formulation F5 has shown 100% drug loading capacity as depicted in Table 2.

Bulk density and tapped density:
The bulk density and tapped density of the formulations were in range of 0.18 to 0.31 and 0.25 to 0.39 respectively. Formulation F5 was having Bulk density=0.31 and Tapped density=0.39 as depicted in Table 3.

Hausner's ratio and Carr's index:
Hausner' ratio were found to be in the range 1.07 to 1.38. Carr's Index was in the range of 6.89 to 28. Formulation F5 was having Hausner's ration 1.25 and Carr's index 20.5 as depicted in Table 3.

Angle of repose:
Angle of repose values of formulations F1 to F8 were found in range 30 to 37. The formulation F5 was having angle of repose 30 as depicted in Table 3.

In vitro Drug Release
The percentage drug release from acyclovir sodium with formulation F5 was observed by using USP Dissolution tester (Type II). These were compared with the pure acyclovir sodium drug as shown in Figure 4. The in vitro drug release showed that the solid lipid microparticles containing acyclovir sodium have sustained the drug release. Formulation F5 showed better sustained release of drug. In vitro release of formulation F5 was 75% after 17hrs shown in Table 4.

DISCUSSION
Acyclovir sodium formulations with DMSO and stearic acid and without DMSO has produced solid lipid micro particles with desirable flow properties and formulation F5 was found to be