Fast Dissolving Tablets of Aloe Vera Gel

Purpose: The objective of this work was to prepare and evaluate fast dissolving tablets of the nutraceutical, freeze dried Aloe vera gel. Methods: Fast dissolving tablets of the nutraceutical, freeze-dried Aloe vera gel, were prepared by dry granulation method. The tablets were evaluated for crushing strength, disintegration time, wetting time, friability, drug content and drug release. A 3 2 full factorial design was applied to investigate the combined effect of two formulation variables amounts of microcrystalline cellulose and mannitol. Results: The results of multiple regression analysis revealed that in order to obtain a fast dissolving tablet of the Aloe vera gel, an optimum concentration of mannitol and a higher content of microcrystalline cellulose should be used. A response surface plot was also provided to graphically represent the effect of the independent variables on the disintegration time and wetting time. The validity of the generated mathematical model was tested by preparing a check point batch. Conclusion: This investigation has demonstrated that satisfactory fast dissolving Aloe vera gel tablets can be formulated. It also showed the potential of experimental design in understanding the effect of formulation variables on the quality of fast dissolving tablets.


INTRODUCTION
The genus, Aloe, belongs to the family, Liliaceae, and includes the species Aloe barbadensis Miller, commercially known as Aloe vera.Aloe vera has been used therapeutically for many centuries and is of particular interest due to its lengthy historic reputation as a curative agent and its widespread use in supplementary therapies.Aloe gel is the colorless gel contained in the inner parts of the fresh leaves 1 .Chemical analysis has revealed that this clear gel contains amino acids, minerals, vitamins, enzymes, proteins, polysaccharides and biological stimulators.The Aloe vera gel, beginning in the 50's, has gained recognition as a base for nutritional drinks and foods [2][3][4] , as a moisturizer, and a healing agent in cosmetics 5 and OTC drugs .
Approximately one-third of the population, primarily, geriatric and pediatric populations, has swallowing difficulties, resulting in poor compliance with oral drug therapy 7 . Fast dissolving tablets offer the combined advantages of performance, convenience, rapid onset of action and patient compliance and allow administration of an oral solid dose form in the absence of water or fluid intake 8 .When placed on the tongue, it disintegrates instantaneously, releasing the drug which dissolves or disperses in the saliva 9 .They are prepared by techniques such as tablet molding, spray drying, lyophilization, sublimation, or addition of disintegrants 10 .Pharmaceutical formulators often face the challenge of finding the right combination of formulation variables that will produce a product with optimum properties.This study was undertaken to formulate a suitable fast dissolving nutraceutical tablet of freeze dried aloe vera gel (AVG), utilizing factorial design.

Other materials
Croscarmellose sodium (CCS), crospovidone (CLP) and sodium starch glycolate (SSG) were purchased from S.D. Fine Chem., Mumbai, India.Microcrystalline cellulose -Avicel PH101 -hereinafter referred to as MCC, was procured from FMC Corporation, Philadelphia, USA.Mannitol was purchased from Merck India Ltd, Mumbai, India.Anhydrous lactose, talc, magnesium stearate and hydrochloric acid were obtained from CDH Chemicals, Delhi, India.Congo red reagent and methylene blue were acquired from Nice Chemicals Pvt.Ltd, Cochin, India.

Preparation of freeze-dried Aloe vera gel (AVG)
The inner mucilaginous parenchymatous tissues of leaves of Aloe vera plants were separated out with the help of a sterile knife.and homogenized in a blender (National blender, Matushita Co. Japan) at 30 rpm.The homogenized mass was separated with a G3 sintered glass filter under vacuum, freezedried using a bench-top freeze-dryer (MC 2L, Cyberlab, USA) and subsequently stored at 4 0 C 11 .The ratio of AVG to lyophilized powder was 200:1.

Preparation of AVG tablets
A preliminary screening of the disintegrantscroscarmellose sodium (CCS), crospovidone (CLP), sodium starch glycolate (SSG) and microcrystalline cellulose (MCC) -was conducted.Mannitol was incorporated as a soluble filler to improve palatability, impart a cooling sensation and sweet taste upon dissolution.Granulation was carried out by the dry granulation technique.All the ingredients were compressed and slugs of 0.8 g were produced at a compression force of 22.0 ± 1.0 kN using flat faced tooling 17 mm in diameter on a single punch tablet machine (Cadmach Machinery Ltd., Ahmedabad, India).
The slugs were then milled and the resulting granules sieved through sieve no.20 USP.The granules were further mixed with a glidant-lubricant blend containing magnesium stearate(1%w/w) and talc (2% w/w) .The granules were compressed using a single punch tablet machine (Cadmach Machinery Ltd., Ahmedabad, India) fitted with 8 mm round standard concave punches.The tablet thickness was about 4.56± 0.06mm.

Hardness test
The crushing strength of the tablets (n=5) was measured using a Monsanto hardness tester (Sheetal Scientific industries, Mumbai , India).

Friability test
The friability of a sample of 20 tablets was measured using a Roche Friabilator (Electrolab, India).Twenty preweighed tablets were rotated at 25 rpm for 4 min.The tablet were then reweighed after removal of fines and the percentage of weight loss was calculated.

Wetting time
The wetting time of the tablets (n=6) was measured using a modified procedure described by Gohel et al 12 .Five circular tissue papers ( Dexina tissues, Gujarat, India) of 10 cm diameter were placed in a Petri dish (internal diameter 10 cm).Water (10 mL) containing methylene blue (10 % w/v), a water soluble dye, was added to the Petri dish.A tablet was carefully placed in the centre of the Petri dish and the time taken for the water to reach the upper surface of the tablets was noted as wetting time.

Disintegration time
This test was performed on 6 tablets.For disintegration time, one tablet was placed in the centre of the Petri dish (internal diameter 10 cm ) containing 10 ml of water and the time taken by the tablet to disintegrate completely was noted 12 .

Drug content uniformity
Colorimetric measurement of glucomannan in the AVG was used for determining drug content uniformity 13 .For the drug content, 10 tablets were weighed and triturated.A tablet triturate, equivalent to 2 mg of AVG, was weighed accurately and dissolved in 100 ml of distilled water and filtered.From this solution, 0.4 ml was transferred to a 10 ml test tube.To this, 4 ml of Congo red reagent (0.01 %) was added with mild vortexing.The mixture was left at room temperature for 20 min and absorbance was measured at 540 nm wavelength using UV-VIS spectrophotometer (SL-196, Elico Ltd).The amount of glucomannan was calculated by interpolating from the standard curve (r 2 =0.9747).

Dissolution studies
The in vitro dissolution study was carried out in a USP dissolution test apparatus (TDT-OP Electrolab, Mumbai India ), type 2 (paddle) with a dissolution media of 900 mL of 0.1 M hydrochloric acid at 50 rpm (37 ºC + 0.5 ºC).Samples (n=6) were withdrawn at the end of 30 min and the dissolution of drug was expressed as percent drug dissolved at the end of 30 min 14 .

Full factorial design
A 3 2 randomised factorial design was adopted to optimize the variables.In this design, two factors were evaluated each at 3 levels and experimental trials were performed at all 9 possible combinations 15 .The amount of disintegrant (MCC) and the soluble filler (mannitol) were chosen as independent variables.The disintegration time and wetting time were selected as the dependent variables.The formulation and evaluation of factorial batches (F1 to F9) is shown in Table 2.The following statistical model incorporating interactive and polynomial terms was used to evaluate the responses: where Y is the dependent variable, b 0 is the arithmetic mean response of the 9 runs, and b 1 and b 2 are the estimated coefficients for the factors X 1 and X 2 respectively.
The main effects (X 1 and X 2 ) represent the average result of changing 1 factor at a time from its low to high value.The interaction terms (X 1 X 2 ) show how the response changes when 2 factors are simultaneously changed.The polynomial terms (X 1 2 and X 2 2) are included to investigate nonlinearity.The multiple regression analysis was performed followed by ANOVA to identify insignificant variables.

RESULTS
Hardness of the tablets was in the acceptable range of 2.56 to 3.55 kg/cm 2 .Friability was 0.51 to 0.82 %.Drug content and release were 100±5% and 82.6-88.4%, respectively.The results of the prelimnary studies (Table 1) revealed that the tablets containing microcrystalline cellulose (MCC) exhibited rapid disintegration and wetting followed by tablets containing croscarmellose sodium (CCS), crospovidone (CLP), sodium starch glycolate (SSG) in that order.

Factorial design
The amount of disintegrant (MCC, X 1 ) and the soluble filler (mannitol, X 2 ) were chosen as independent variables in a 3 2 full factorial design.The disintegration time and wetting time were selected as the dependent variables.The data (Table 2) clearly indicates that disintegration time and wetting time are strongly dependent on the selected independent variables.The fitted equations (full and reduced) relating the responses, disintegration time and wetting time, to the transformed factor are shown in Table 3.

Preliminary trials
In order to select the best disintegrant, four disintegrants were studied in preliminary trials.The efficiency of disintegrants can be affected in varying magnitudes by the presence of a soluble filler in the tablet formulations 16 .This is expected due to the fact that the quantity of water penetrating into the tablet bed is limited.The soluble filler (mannitol) has good aqueous solubility, negative heat of solution and good wetting properties 17 .Mannitol will consume water partially, leaving only a part of the total water to penetrate into the tablet for the development of force necessary for disintegration.The results of the preliminary studies (Table 1) revealed that the tablets containing microcrystalline cellulose (MCC) exhibited rapid disintegration and wetting.MCC has good wicking and absorbing capacities 18 .Tablets of MCC disintegrated rapidly due to the rapid passage of water into the tablets resulting in the instantaneous rupture of the hydrogen bonds 19 .The delayed disintegration and wetting time of the tablets formulated using other disintegrants could be attributed to their slow water uptake and high gelling tendency.Based on the results of the preliminary study, MCC was selected as the disintegrant for further studies.The optimum concentration of MCC may be less than 12 %.

Factorial design
The polynomial equations can be used to draw conclusions after considering the magnitude of coefficient and the mathematical sign it carries (i.e., positive or negative).Table 4 shows the results of the analysis of variance (ANOVA), which was performed to identify insignificant factors.The high values of correlation coefficient for disintegration time and wetting time (Table 4) indicate a good fit.The equations may be used to obtain estimates of the response as a small error of variance was noticed in the replicates 20 .

Full and reduced models
The significance level of coefficients, b 12 and b 11 , were found to be more than 0.05, hence they were omitted from the full model to generate the reduced model.The results of statistical analysis are shown in  show that for both disintegration time and wetting time, the amount of MCC (X 1 ) had a negative effect while the concentration of mannitol (X 2 ) had a positive effect.It means that as the amount of MCC is increased, both the disintegration time and wetting time decreases, while as the amount of mannitol is increased both the disintegration time and wetting time would increase.Therefore, a high level of MCC and low level of mannitol should be selected for the rapid disintegration of the tablets.The relationship between the dependent and independent variables was further elucidated using surface response plots.The data of the response surface plot (Figures 1 and 2)) demonstrate that both X 1 and X 2 affect the disintegration and wetting times.Based on the foregoing, discussion batch F6 (disintegration time: 33.24 sec and wetting time: 29.62 sec) was selected as a promising batch.A checkpoint batch was prepared at X 1 = + 0.8 level and X 2 = -0.2level.The values of disintegration and wetting times expected from the reduced model for this batch are 33.78 and 29.32 sec, respectively.Table 2 indicates the results were as expected.Thus, the statistical model is mathematically valid.

CONCLUSION
The results of a 3 2 full factorial design revealed that the amount of microcrystalline cellulose and mannitol significantly affect the dependent variables -disintegration and wetting times.The present study has revealed the feasibility of optimization procedure in developing AVG fast dissolving tablets.
material A. vera plants were collected (March 2003) and authenticated by Dr. C.S. Pandey of Medicinal Plant Research and Development Centre, Govind Pant University of Agriculture and Technology, Pantnagar (Uttarakhand), India.A voucher specimen (AV-8) was retained in our museum for future reference.

Figure 1 :
Figure 1: Response surface plot for disintegration time

Figure 2 :
Figure 2: Response surface plot for wetting time

Table 1 :
Tablet formulation and evaluation of preliminary trials* *All batches contained 2%w/w talc and 1%w/w magnesium stearate.

Table 3 :
Summary of results of regression analysis*

Table 4 :
Calculations for testing the model in portions*