INTRODUCTION:

Between 1940s and 1960s, the concept of microencapsulating technology began as an alternative means of delivering drugs¹. It continued guest for more refined system, in 1980s polymer membrane technology came to be known at forefront. Further, the process of targeting and site specific delivery with absolute accuracy has been shown to be achieved by attaching bioactive molecule to liposome’s, bio-erodible polymer, implants, monoclonal antibodies and various particulate carriers (e.g. Nanoparticles and Microspheres, etc)

The micro particulates delivery system are considered and accepted as a reliable means to deliver the drug to the target site with specificity and to maintain the desired concentration at the site of interest without untoward effects

Poor patient compliance is the single common reason for the failure of chemotherapy of tuberculosis. One useful method to ensure compliance is to supervise the administration of drug, which is not always practical.

An alternative approach is to utilize the carrier delivery system in a sustained release manner at therapeutic concentration over a period of time. This strategy helps to improve patient compliances. To minimize toxicity and improve patient’s compliance, extensive progressive efforts have been made to develop various implants, microparticles and various other carrier based drug delivery systems to reduce the dosing frequency, which forms an important therapeutic strategy to improve patients outcomes ^{2, 3}.

The natural polymers like alginate have been used to develop drug delivery system for entrapping the delivering drugs orally.⁴Sodium alginate a salt of alginic acid, has ability to form a gel in the presence of divalent cations like calcium. This gel shrinks at acidic pH and erodes at alkaline pH. Therefore, it can be used effectively to deliver drug to the intestine. Thus an objective of the present study was to develop an alginate based oral drug delivery system for rifampicin, in order to improve patient compliance and minimize potential toxicity.

Table 1. Coat composition, microencapsulation efficiency of the microparticles

Formulations	Core: coat ratio	Encapsulation efficiency (%)
F1	2:1	74
F2	2:2	69
F3	2:3	80
F4	2:4	64

EXPRIMENTAL METHODS:

MATERIALS:

Rifampicin was received as a gift sample from Micro Labs Ltd,Hosur, India. Sodium Alginate was kindly supplied by Alkem Laboratory Mumbai, India All other chemical were purchased from Qualigens fine chemicals, Mumbai, India. And all are of laboratory grade.

METHODS:

1. PREPARATION of MICROPARTICLES:

Alginate microparticles were prepared by the method of Rajaonarivony et al. with slight modifications⁵. The principle involves cation-induced controlled gelification of alginate. Briefly, calcium chloride (0.5ml,18mM) was added to 9.5 ml of sodium alginate solution (0.06%w/v) containing Rifampicin. 2 ml of chitosan solution (0.05%w/v) was added, followed by stirring for thirty min. and storage at room temperature overnight. Drug loaded microparticles were recovered by centrifugation at 8000 rpm for 35 min. and washed thrice with distilled water. The ratio of core -coat materials used was 2:1, 2:2, 2:3 and 2:4. All other formulations were prepared in the similar manner.

Fig 1. In-vitro release profile of pure drug rifampicin

2. evaluation of entrapment efficiency:

The drug loading capacity of alginate microparticles was detected by soaking them in phosphate buffer solution after filtering through nylon disc filter. The concentration of drug was analyzed by UV-spectrophotometer at λ 475 nm⁶.

Drug entrapment efficiency capacity was calculated using the formula,

Drug entrapment efficiency =

estimated % drug content_ × 100

Theoretical % drug content

3. DISSOLUTION STUDIES:

In-vitro release study was carried out by rotary shaking method for 72 hrs in the physiological fluid (pH 7.4 phosphate buffer solution) samples were withdrawn at appropriate intervals and fresh sample were replaced. The withdrawn samples were diluted and absorbance was analyzed by an UV spectrophotometer (Shimadzu-1700) at 457 nm. The drug content was calculated using the equation generated from standard calibration curve.

Fig 2. In-vitro release profile of the prepared microparticles F1, F2, F3, F4

4. Drug excipient compatibility study⁷:

Drug excipient compatibility was detected by Fourier-transfer infrared spectroscopy analysis. FTIR spectra were recorded on FTIR (SHIMADZU CORP, Japan) samples were compressed with potassium bromide and scanned between 4000-400 cm^-1

5. Particle size analysis:

Particle size analysis was performed with the help of laser channel beam (CIS-50, Anskermid, Nitherland). The mean particle size was detected.

6. Scanning electron microscopy ANALYSIS:

To detect the surface morphology of the microparticles, SEM was performed using scanning electron microscope (JEOL-JSM-6306, Japan) with a 10-kv accelerating voltage.

Fig 3. SEM photograph of pure drug

7. Drug release kinetics⁸:

The In-vitro dissolution data were fitted to the Korsmeyer and Peppas equation⁸

M_t/ M_∞ = k.t _n

Where Mt/ M_∞represents the fraction of drug released at time t; k is the release rate constant; n is diffusion coefficient

Table 2. Mathematical modeling and drug release kinetics of formulated microparticles

Formulations	n	k	Mechanism
F1	0.511	0.963	Anomalous
F2	0.501	0.983	Anomalous
F2	0.416	0.890	Fickian
F4	0.741	0.999	Anomalous

RESULTS AND DISCUSSION:

ENTRAPMENT EFFICIENCY:

The entrapment efficiency of rifampicin within alginate based microparticles is shown in (Table. 1). Some drug was lost to the external phase during preparation and recovery. The results in Table. 1 also indicates that the loading efficiency in the alginate based microparticles depends upon the preparation conditions. The incorporation efficiency of drug appeared to be low at all cross linking densities. The highest drug % entrapment was observed for the formulation F3 (80%). This fact is well supported by Wang, D. et. al. 1997.⁹

The in-vitro release studies of microparticles in physiological fluid are shown in Fig 2 and Fig 3. Formulations F1, F2, F3, and F4 show the 88.5, 76.5, 82.76 and 40.76 % drug release at the end of 72 hrs. This showed better sustained release profile when compared to release of pure drug sample which was almost 87% in 3 hrs. The data clearly indicate the drug release can effectively be controlled by varying the ratio of core -coat materials of the microparticles.

The rate of release of rifampicin from alginate based microparticles followed a biphasic kinetics mechanism; an initial fast release mainly caused from the dissolution of non encapsulated drug from the surface of the microparticles, followed by a much slower release rate controlled by the rate of swelling of polymeric matrix and the simultaneous diffusion of Rifapicin from the interior of microparticles.

The concentration of sodium alginate used in the microparticles preparation can modify the release behavior of the drug from the produced microparticles. When a more concentrated polymer solution was initially employed for synthesis of the microparticles, the drug was more effectively entrapped into the polymer matrix, but it resulted in slow release rate, but when lower concentration of Sodium alginate was used the higher release rate was observed in the formulation¹⁰.

FTIR studies revealed that there was no shift in the peaks. Indicating there is no interaction between rifampicin and other ingredients used.

The microparticles prepared were found to be small and free flowing. The resulting microparticles were characterized for their surface morphology by SEM analysis (Fig 3and Fig 4) and particles found to be non spherical and rough surfaced because of less water solubility. The size analysis revealed the mean particle size of microparticles as 0.74µm with a standard deviation of 0.05µm.

Fig 4. SEM photograph of best formulation F1

The dissolution data was treated with different kinetic equations to interpret the order of release shown in Table 2 .The n value for formulation F1, F2, F4 are 0.511, 0.501, 0.741 respectively; this indicates that the formulation follows the Anomalous type of mechanism but the n value for the formulation was 0.416 which indicated Fickian diffusion mechanisms

CONCLUSION:

The sustained release profile of rifampicin by loading in to alginate microparticles was successfully developed using a cation-induced gelification alginate technique.

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Received on 23.11.2008 Modified on 25.12. 2008

Research J. Pharm. and Tech.2 (2): April.-June.2009,; Page 301-303