Neem Gum as an Alternative to Synthetic Pharmaceutical Excipients

Introduction

Acacia, tragacanth, guar gum, xanthan gum, starch, agar, alginates, carrageenan, pectin, gelatin, and cellulose are only a few examples of plant-based pharmaceutical additives. In the pharmaceutical manufacturing, these natural excipients are used as binding agents, sustaining agents, disintegrants, protectives, thickening agents, gelling agents and stabilizers. Natural plant-based excipients provide the following advantages: local availability, low cost, relatively free of adverse effects, biocompatible and improved patient tolerance. Usage of natural substances improves the national economy by providing inexpensive formulations to society, by using locally available materials.¹

Gum is a versatile byproduct formed as a consequence of certain metabolic mechanisms in plants and trees. Plantderived gum is either water soluble or absorbs water to form a viscous solution. Neem gum contains mannose, fructose, glucosamine, arabinose, galactose, xylose and D-glucuronic acid. Neem’s gum, which is used in a number of industries has been economically exploited. Neem tree is being grown on a large-scale basis for using all its parts, no wonder it is called a ‘Universal Tree’, having a cure for almost everything. There hasn’t been much research on using neem gum as a tablet binder or a suspending agent for pharmaceutical suspensions. Hence, in the current research, neem gum was selected to evaluate its binding and suspending potentials using aceclofenac as a model drug.^2-3

Materials and Methods

Aceclofenac was purchased from Yarrow Chem, Pvt. Ltd and neem gum was extracted in our laboratory. Analytical grade mannitol, sodium starch glycolate, magnesium stearate, talc, sodium carboxymethylcellulose (CMC), methyl paraben, propyl paraben and vanillin flavor were used in the present study.

Processing of neem gum

The neem gum was collected from the neem trees in the month of October-November from the surrounding regions of the Tumkur. Gum was collected from the neem trees by making incisions and left over for few days to produce the gum. The gum was collected and allowed to dry at room temperature before being used. The dried gum was ground in a mortar and passed through sieve No.60. In distilled water, neem gum (25 g) was solubilized (250 ml) and to this solution 20 ml of acetone was added to precipitate gum. The precipitate of gum was dissolved in 50 ml of water and 20 ml of ethanol was added to precipitate the gum again. It was separated by using muslin cloth, air dried, pulverised and kept in an airtight container. Purified neem gum 18 g was obtained out of 25 g of original gum.⁴

Phytochemical screening of neem gum

The presence of alkaloids, glycosides, carbohydrate, proteins, amino acids, mucilage and tannins, was determined.⁵ (Table 1)

Determination of pH

Neem gum (2 g) was dissolved in distilled water (100 ml), whose pH was measured using a pH meter.

Measurement of viscosity

A digital Brookfield viscometer was used for the measurement of viscosity of gum solution (5 & 7.5 %w/v). The spindle speed rotation was kept at 20 rpm.

Loss on drying

Accurately 5 g of neem gum was weighed and dried at 100 ± 2°C using hot air oven to get constant weight of the gum (Table 2).

Fourier-transform infrared (FT-IR) studies

These investigations were carried out to see whether there was any interaction between the aceclofenac and the neem gum in addition to the excipients used in the formulation. Physical mixture of drug, excipients and tablet formulations were studied for FT-IR spectra. Whatman filter paper was used to filter the aceclofenac suspension formulation, and the residue was employed for the FT-IR investigation.⁶

Scanning electron microscopy

To further understand the surface morphological characteristics of purified neem gum powder, SEM experiments were performed.

Differential scanning calorimetry (DSC)

To see if there were any chemical interactions between pure aceclofenac, neem gum, and tablet formulation F4, DSC tests were conducted.

Preparation of aceclofenac tablets

The aceclofenac tablets were made using a wet granulation process.⁷ Aceclofenac was used as model drug. Individually, the drug and ingredients were passed through the sieve no. 60. Aceclofenac, neem gum, sodium starch glycolate, and mannitol were all added to the mixture and blended evenly. A sufficient amount of distilled water was added to make a wet mass, which was then passed through sieve no. 12. As a granulating fluid, distilled water was used. The same method was used to make granules with different concentrations of neem gum (2.5, 5, 7.5, and 10% w/w). For comparison, a 7.5 percent w/w concentration of polyvinylpyrrolidone (PVP) was employed as a synthetic binding agent (Table 3). The pre-compression parameters of the prepared granules were evaluated. Granules were treated with talc and magnesium stearate before being compressed into 200 mg tablets using a rotary tablet compression machine with ten stations. (Shakti Pharma Tech, Ahmedabad).

Evaluation of aceclofenac granules

Angle of repose

Granules were carefully poured through a glass funnel until the apex of the conical pile just touched the tip of funnel.⁸ Using the below formula, the angle of repose was estimated.

(n)

Where,

             h = pile height, r = radius of the base of the pile, θ = angle of repose,

Compressibility index

Using a measuring cylinder, the density of tapped and untapped mass was determined. The compressibility index was calculated based on the following formula:

Percent compressibility index

(2)

Evaluation of tablets⁹

Weight variation test

Twenty tablets were chosen at random and weighed individually and combined in a single pan balance. The average weight was taken into consideration and standard deviation was calculated.

Hardness, thickness

The Mansanto hardness tester was used to determine the hardness of six tablets at random. Unit of hardness was in kg/cm². The thickness and diameter of the tablets were measured with Vernier calipers.

Friability

The friability test was done with the help of Roche friabilator (Campbell Electronics, Mumbai, India). Initial weight of ten tablets was noted as W1 g and after the test, it was noted as W2 g. After that, the formula was used to calculate the percentage friability.

Percentage Friability =

                (3)

Drug content

Five tablets were separately weighed and crushed together. The drug content was evaluated spectrophotometrically. For extraction of drug, weight of powder taken was equivalent to average weight of tablets. Phosphate buffer with pH 6.8 was used to extract the drug. Suspension (5 ml) was used for extraction with phosphate buffer pH 6.8 and the absorbance was measured using a UV spectrophotometer at 274 nm after appropriate dilution.

Disintegration and dissolution test¹⁰

The disintegration test was carried out using the I.P. method. Six tablets were placed in disintegration apparatus glass tubes. The temperature of the disintegration fluid was kept at 37 ± 2°C. To carry out dissolution studies, phosphate buffer with pH 6.8 at 37 ± 1°C was used and the paddle’s rotation speed was kept at 50 rpm. A tablet was placed in dissolution media and samples were taken every 10 minutes until 90 minutes.

When it came to suspension, samples were taken until 20 minutes at every 2 minutes. To keep the 900 ml volume constant, the dissolution media was refilled every time. Samples were analyzed by UV spectrophotometer at 274 nm. Acenac, a commercialized tablet was also tested for dissolution experiments for comparison purposes.

Preparation of aceclofenac suspension

In a mortar, one gram of aceclofenac and 0.25 gm of neem gum were taken and triturated to a fine powder. Then a little amount of distilled water was added and the trituration process was repeated. Methyl paraben, propyl paraben, and vanillin were added in adequate amounts, and the volume was adjusted to 50 ml using distilled water (Table 4) and stored in well-closed dispensing bottles. Similarly, different concentrations of neem gum (1, 1.5, and 2 percent w/v) were used to make aceclofenac suspensions. For comparison, a reference aceclofenac suspension was made with 1.5 percent w/v sodium CMC as a synthetic suspending agent.¹¹

Evaluation of aceclofenac suspension pH measurement

A digital pH meter was used to measure the pH of the suspensions (without dilutions), once a week for three weeks.

Sedimentation volume¹²

Each suspension (50 mL) was put into a 100 ml measuring cylinder and was kept at room temperature for 7 days. The volume of the sediment was measured every hour for seven hours, then every 24 hours for seven days. For comparison, the commercial product IMOL was chosen.

Sedimentation volume of various suspensions was estimated by the following equation.

(4)

Where,             

F = sedimentation volume

Vu = ultimate volume of the sediment

Vo = original volume of the of suspension

Redispersibility

Each suspension (50 ml) was kept in stoppered dispensing bottles for 7 days at room temperature. One bottle was collected and turned upside down at regular intervals until there was no sediment at the bottom and the number of rotations was recorded.¹³

Determination of flow rate

10 ml of suspension was taken in a pipette and the time taken by suspension to come out was noted to calculate the suspension flow rate.

(5)

Viscosity

The Brookfield Synchroelectric viscometer (model LVF, Spindle #2 rpm was kept 25 & 50) was used to measure the viscosity of the samples at 25°C. All the results were triple-checked.

Particle size analysis

A microscopic approach was used to determine the particle size in the prepared suspensions. Suspension droplet was taken on a glass slide, the size of the particles was determined using a calibrated eye piece micrometer.¹⁴

Degree of flocculation

The degree of flocculation was estimated using the equation below.

(6)

Where,

F = flocculated suspension’s ultimate sedimentation volume

F_∞ = deflocculated suspension’s ultimate sedimentation volume

Stability studies

Stability tests of best formulations were done according to ICH requirements, which included storing the tablets for three months at 40 ± 2°C / 75 ± 5% RH.

Results

The three tests Molish, Fehling, and Barford produced positive results for neem gum, according to phytochemical characterization of neem gum data. This indicated that neem gum was high in carbohydrates and reducing sugar. Glycosides, proteins, alkaloids, tannins, and amino acids, on the other hand, were not present.

According to physicochemical study, neem gum was soluble in water but insoluble in acetone and other organic solvents. The neem gum solution had a pH of 6.26. Microbial growth was discovered to be nonexistent after further study. Total ash, water soluble ash, and acid insoluble ash, all had percentages of 8.56, 6.59, and 0.59, respectively.

The FT-IR spectra of pure aceclofenac, neem gum, an optimized aceclofenac tablet (F4), and aceclofenac suspension (F9) are shown in Figure 1. Drug corresponding absorption peaks can also be observed in optimal tablet and suspension dosage forms, that determine compatibility of drug with formulation excipients.

A strong endothermic peak at 156.25 °C could be seen in the DSC thermogram of aceclofenac (Figure 2), but not for pure neem gum. However, an endothermic peak observed at 165 °C which belongs to mannitol used in the formulation.

SEM images of neem gum powder at 250 and 2000 times magnification are shown in Figure 3. The neem gum particles had a smooth surface and an uneven form.

The particles were 50 to 200 micrometres in size.

The angle of repose of the granules was between 26 and 28 degrees, indicating adequate granule flow. Granule bulk density was found to be between 0.51 and 0.59 g/ cc, whereas tapped density was found to be between 0.59 and 0.65 g/cc. The Haunser ratio was between 1.09 and 1.13, and Carr’s index of granules was 9.14-12.63 (Table 5). These values are suitable for granule compression.

The hardness of aceclofenac tablets ranged from 3.24 to 5.94 kg/cm2 . The percentage of friability ranged from 0.45 to 0.86 percent. The thickness varied between 2.17 and 2.92 mm (Table 6). As a result, tablets containing neem gum as a binding agent possessed the desired characteristics.

The particle size of all suspension formulations was determined to be in the range of 9 - 15 µm by microscopic techniques. The viscosity of all formulations was determined to be 16.12 - 29.69 cps at 25 and 50 rpm, respectively. The degree of flocculation ranged from 1 to 1.15. The flow rate for several suspensions varied from 0.30 to 1.66 ml/min. Suspension drug content was found to range between 97.15 and 101.06 percent (Table 7).

The percentage sedimentation volume rose as the suspending agent concentration in the suspension formulation was raised. The volume of sedimentation in each suspension, on the other hand, was inversely proportional to the number of days. As the time went from zero to seven days in case of the F6 formulation, the percentage sedimentation volume decreased from 100 to 62 (Table 8, Figure 4). Formulation F9, on the other hand, had a sedimentation volume of 98 percent. As a consequence, F9 was selected as the most effective formulation. The redispersibility and pH ranges were determined to be 1 - 3 turns and 5.32 - 6.27 pH (Table 9).

In vitro studies of aceclofenac tablet release found that 98.27% of the drug was released after 60 minutes in the case of formulation F1. Formulation F2 released 98.36% after 70 minutes, formulation F3 released 98.38% after 80 minutes, and formulation F4 released 99.65% after 90 minutes. In vitro studies of suspension release found that 97.92% of the drug was released within 14 minutes in case of formulation F6. Formulation F7 released 98.57% in 16 minutes, while formulations F8 and F9 released 99.13% and 99.31% in 20 minutes, respectively. Three months of stability testing for optimized formulations were conducted at 40 ± 2°C / 75 ± 5% RH. Neither the physical property nor the drug content changed appreciably during the study period.

Discussion

The unique absorption peak of pure aceclofenac was retained in the FT-IR spectrum of a tablet formulation. However, due to the decreased concentration of the drug in suspension, FTIR investigations on aceclofenac suspension (in its original form) indicated less intense absorption peaks for the drug in the relevant spectrum. As a result, the suspension was filtered and the residue was used in the experiments. According to the data, the drug’s absorption peaks were also observed in the residue. There were no variations in drug absorption between the tablet and suspension final formulations. As a result, no interaction exists between the aceclofenac and the neem gum or other excipients used. As a result, neem gum can now be used as an excipient in tablet and suspension formulations. DSC tests found that pure aceclofenac sodium has a prominent endothermic peak (Figure 2A) at 156.25°C, indicating that it has a crystalline structure. Pure neem gum lacks a prominent endothermic peak, indicating that it is amorphous. Drug endothermic peak appeared at slightly lower temperature i.e. 150°C in the thermogram of tablet formulation (Figure 2C), but the shape of peak was retained. However, endothermic peak at 165°C was observed which corresponds to mannitol. Mannitol was used as diluent in the tablet formulation. The aceclofenac had no interaction with the excipients, according to DSC tests. The amount of time it required to release roughly 98% of the aceclofenac from different tablet formulations increased as the percentage of neem gum in the tablet formulation increased, according to in vitro drug release data. As mentioned in Table 10 and Figure 5, formulation F5 prepared with the synthetic binding agent PVP released 99.22% of the drug during 90 minutes of dissolution trials, while the commercial version released 99.12%.

Even though formulations F1, F2 & F3 released 98 percent of the medication earlier than formulation F4, formulation F4 was optimized, since formulations F1, F2 & F3 lacked enough hardness and failed the friability test. Similarly, as the percentage of neem gum in the suspension formulation increased, as shown in Table 11, Figure 6, the time taken to release about 98% of the drug from different suspension formulations increased. Despite the fact that formulations F6, F7, and F8 released 98% of the drug earlier than formulation F9, formulation F9 is optimal due to the fact that formulations F6, F7, and F8 did not have enough percentage sedimentation volume. The developed tablet and suspension formulations had release kinetics that are close to zero order, and the release mechanism was identified to be a non-Fickian model.

Conclusion

The neem gum was effective in acting as a good binding and suspending agent for the aceclofenac tablets and suspension. The developed tablet and suspension formulations had released aceclofenac similar to zero order and the release mechanism followed was non-Fickian model. Neem gum can be selected as a binding and suspending agent at 10% w/w and 2% w/v, respectively.