Isolation and evaluation of Basella alba linn. Leaf mucilage as release retardant in tablet formulation

Yamunappa¹, Ravi Kumar^*1, Pooja Shetty, Prathibha Suvarna, Narayana Swamy VB²

¹Department of Pharmaceutics, Karavali College of Pharmacy, Mangalore

²Department of Pharmacognosy, Karavali College of Pharmacy, Vamanjoor, Mangalore

*Corresponding Author E-mail: yamunappa12@gmail.com

ABSTRACT:

In recent years, plant derived polymers have evoked tremendous interest due to their diverse pharmaceutical applications such as diluent, binder, disintegrate in tablets, thickeners in oral liquids, protective colloids in suspensions, gelling agents in gels and bases in suppository, they are also used in cosmetics, textiles, paints and paper-making. Basella alba is a wildly cultivated, cool season vegetable with climbing growth habit. Malabar spinach is high in vitamin A, vitamin C, iron and calcium. In the present work, an attempt was made to develop matrix tablets of diclofenac using natural release retardant isolated from Basella alba leaves and its efficiency was compared with most widely used natural release retardant like guar gum.

Diclofenac matrix tablets were formulated by using BAM in different concentrations (2.5%, 5%, 7.5%, 10% and 12.5%) by wet granulation method and its efficiency was compared with guar gum. The granules prepared were free flowing with good compressibility. Formulated tablets were evaluated for hardness, thickness, friability, weight variation, drug content, in vitro disintegration time, swelling studies and in vitro dissolution studies.

The hardness of the tablets was found to be 6-7 kg/cm2 and percentage friability of tablets was found to be less than 0.1% in all the cases and swelling index studies shown that as the conc. of polymer increased there was a proportional increase in the swelling index of tablet. Among the formulation studied, formulation F5 showed release of drug more than 12hrs and formulation F5 showed optimum release characteristics. The release was found to follow the anomalous non-Fickian diffusion. It revealed that as the conc. of polymer in tablet increased the release of the drug from the tablet decreased. It shown that BAM exhibited excellent retarding effect on drug release from the matrix tablets even at very low concentrations. Stability studies were carried out at 400C±20C/75%±5% RH for formulation F5 for 30 days. The results of stability studies indicated no significant changes with respect to physicochemical properties, in vitro disintegration time, swelling index and in vitro drug release.

KEYWORDS: Matrix tablets, diclofenac, Basella alba mucilage, release retardant, wet granulation, guar gum.

INTRODUCTION:

Excipients were defined as ‘the substance used as a medium for giving a medicament’, that is to say with simply the functions of an inert support of the active principle or Principles¹.

The specific application of natural polysaccharide polymers in pharmaceutical formulations include to aid in the processing of the drug delivery system during its manufacture, protect, support or enhance stability, bioavailability or patient acceptability, assist in product identification, or enhance any other attribute of the overall safety, effectiveness or delivery of the drug during storage or use².

Today we have several pharmaceutical excipients of plant origin, like starch, agar, alginates, carrageenan, guar gum, xanthan gum, gelatin, pectin, acacia, tragacanth, and cellulose. These natural excipients find applications in the pharmaceutical industry as binding agents, disintegrates, sustaining agents, protective colloids, thickening agents, gelling agents, bases in suppositories, stabilizers, and coating materials. The advantages of natural plant-based excipients include that they are of low cost, natural origin, fairly free from side effects, biocompatible, and bio-acceptable, with a renewable source, environmental friendly processing, local availability, better patient tolerance, as well as public acceptance³. Excipients are also derived from natural sources, synthesized chemically, or prepared semi-synthetically starting from natural sourced materials.

They range from simple, usually well-characterized, organic or inorganic molecules to highly complex materials that are difficult to fully characterize. Classification of excipients is based on their role in the pharmaceutical formulation, their interactions influencing drug delivery, or their chemical and physico-chemical properties⁴.

Excipients are also sometimes used to bulk up formulations that contain very potent active ingredients, to allow for convenient and accurate dosage. Depending on the route of administration, and form of medication, different excipients may be used. To stabilize the active ingredient, excipients are added, ensuring that the active ingredient stays "active", and, just as importantly, stable for a sufficiently long period of time that the shelf-life of the product makes it competitive with other products. Excipients also can serve to mask an unpleasant taste or texture and help ensure that the right amount of the API makes it to the right spot in the body at the right time⁵.

Robbins has stated, "in spite of the problems which have beset the gums market in recent years, the fact remains that in many cases the gums provide a valuable source of income for many poor smallholders or itinerant laborers, either in very poor countries or in the poorest regions rather than more developed countries as such they are important commodities ...". This remains true today. Tens of thousands of people worldwide, living in regions ranging from semiarid deserts to rainforests depend on the collection of gums, resins and latexes in order to provide them with an income. Equally, many millions of people around the world make use of these products in their everydayLife⁶.

Mother Nature has gifted India with great variety of flora and fauna. For centuries man has made effective use of materials of natural origin in the medical and pharmaceutical field. Today, the whole world is increasingly interested in natural drugs and excipients.

Natural materials have advantages over synthetic materials because they are non-toxic, less expensive and freely available. Furthermore, they can be modified to obtain tailor made materials for drug delivery systems allowing them to compete with the synthetic products that are commercially available. Many kinds of natural gums are used in the food industry and are regarded as safe for human consumption. It should be noted that many ‘old’ materials are still popular today after almost a century of efforts to replace them. It is usual to strike a balance between economics and performance in the face of commercial realities^7-10.

Over the Past 30 years, as the expense and complications involved in marketing new drug entities have increased, with concomitant recognition of the therapeutic advantages of Sustained drug delivery, greater attention is being paid on development of oral sustained release drug delivery systems. The goal in designing sustained release drug delivery system is to reduce the frequency of the dosing, reducing the dose & providing uniform drug delivery. So, Sustained release dosage form is a dosage form that releases one or more drugs continuously in predetermined pattern for a fixed period of time, either systemically or locally to specified target organ. Sustained release dosage forms provide better control of plasma drug. The model drug selected for investigation is diclofenac which is an non-steroidal anti-inflammatory drug (NSAID) drug taken to reduce inflammation and as an analgesic reducing pain in conditions such as arthritis or acute injury. It can also be used to reduce menstrual pain, dysmenorrheal pain. Basella alba which is a fast-growing, soft-stemmed vine, reaching 10 m in length. Its thick, semi-succulent, heart-shaped leaves have a mild flavour and mucilaginous texture. The ethno medicinal plant Basella alba belongs to the family Basellaceae, and commonly known as Malabar spinach, Indian spinach, ceylon spinach and vine spinach. Stem, petiole, leaf and peduncles are green in colour. The perianth tube is greenish white in the basal and pink in apical regions. Typical of leaf vegetables, Malabar spinach is high in vitamin A vitamin C, iron and calcium. It is low in calories by volume, but high in protein per calorie. The succulent mucilage is a particularly rich source of soluble fiber. The mucilaginous qualities of the plant make it an excellent thickening agent in soups, stew, etc., where it can be used as a substitute for okra, Abelmoschus esculentus. Hence there is a need of development of plant based pharmaceutical excipients for the formulation of the different pharmaceutical formulations. In the present investigation, an attempt has been made to isolate mucilage from Basella alba leaves, followed by physicochemical and phytochemical characterization of the isolated mucilage, toxicity studies and exploration of release retardant property of isolated mucilage in sustained release matrix tablets. By this we can provide inert, less expensive, and chemically inert natural excipients that can compete with the available synthetic and semi-synthetic excipients that can be used as an effective alternative excipient for synthetic excipients for the formulation of pharmaceuticals.

MATERIALS AND METHODS:

Materials:

Diclofenac sodium was obtained from BPRL, Bangalore, India as gift sample. Basella alba linn. leaf was procured from the local market in Mangalore. All the other solvents, reagents and chemicals used were of either Pharmacopoeial or analytical grade.

Methods:

Isolation and purification of mucilage from Basella alba leaves:¹¹

The leaves of the Basella alba were brought from vegetable market of Mangalore (India). The collected leaves were sun dried for 10 days. The coarse powdered leaves were defatted using petroleum ether (60°-80°C) in a Soxhlet apparatus. The defatted material (60gm) was soaked in distilled water (1000ml) at room temperature for 6hr.

After soaking material was reflux on water bath at 70°C for 2 hr. The viscous solution was passed through eight fold of muslin cloth. Acetone was added slowly to filtrate till precipitation is completed. The precipitated mucilage was separated and washed thrice with acetone to remove the traces of water. The separated mucilage was spread on glass plates and dried at 40°C. The dried mucilage was tested for its phytochemical tests and physicochemical characterization.

Drug-Excipient Compatibility study:

This study has been done to check whether there is any compatibility related problems are associated with drug and excipients used for the formulation of tablet.

Fourier Transform Infrared (FTIR) Spectral analysis:

FTIR spectra of pure drug and physical mixture of drug and excipients were recorded on samples prepared in potassium bromide (KBr) disks using a FTIR Spectrophotometer, (FTIR-8300, Shimadzu, Japan). Samples were prepared in KBr disks by means of a hydrostatic press at 6-8 tons pressure. The scanning range was 400 to 4000 cm^-1.

Differential Scanning Calorimetry (DSC) analysis:

DSC analysis was performed using Shimadzu DSC-60, Shimadzu Limited Japan. A 1:1 ratio of drug and excipient was weighed into aluminum crucible. And sample was analyzed by heating at a scanning rate of 20⁰C over a temperature range 40-430⁰ C under nitrogen environment.

Formulation of diclofenac sodium matrix tablets:

Sustained release matrix tablets of diclofenac sodium with BAM were prepared using different concentration of BAM viz., 2.5, 5, 7.5,10 and 12.5%w/w. BAM was used as matrix forming material. Wet granulation method was used to prepare granules of drug using IPA: water (3:1) as binder solvent, lactose as diluent, and mixture of talc and magnesium stearate as glidant and lubricant respectively. BAM was included in the formulations containing 100 mg of diclofenac sodium. BAM were passed though mesh no. 85 and mixed with Diclofenac Sodium and lactose which was previously passed through mesh no. 85. The powders were mixed, granulated with IPA: water (3:1) and the wet mass was passed through mesh no.12. The wet granules obtained were dried at 40°C. The dried granules were subjected to dry screening by passing through mesh no. 16, blended with a mixture of talc and magnesium stearate and compressed into tablets using rotary tablet press (Cemach, Ahmedabad, India). Similar procedure was employed for preparation of diclofenac tablets using 12.5%w/w guar gum as a known matrix polymer. The compositions of each formulation were shown in Table 1.

Table 1: Composition of different batches of diclofenac sodium matrix tablets

Ingredients (mg/tablet)	Formulations
Ingredients (mg/tablet)	F1	F2	F3	F4	F5	F6
Diclofenac Sodium	100	100	100	100	100	100
BAM*	6.25	12.5	18.75	25	31.25	--
Guar gum	--	--	--	--	--	31.25
Lactose	130	123.75	117.5	111.25	105	105
Aspartame	2.5	2.5	2.5	2.5	2.5	2.5
Orange flavour	2.5	2.5	2.5	2.5	2.5	2.5
Magnesium stearate	5	5	5	5	5	5
Talc	2.5	2.5	2.5	2.5	2.5	2.5
Aerosil	1.25	1.25	1.25	1.25	1.25	1.25
Total weight of tablet	250	250	250	250	250	250

*BAM: Basella alba mucilage; # All quantities are in milligrams;

# all the batches contained 1% w/w talc and 2% w/w magnesium stearate

Evaluation of diclofenac sodium granules:

Angle of repose:

The angle of repose of granules was determined by the funnel method. The accurately weight granules were taken in the funnel. The height of the funnel was adjusted in such a way the tip of the funnel just touched the apex of the powder blend. The granules were allowed to flow through the funnel freely on to the surface. The diameter of the granules cone was measured and angle of repose was calculated using the following equation.

tan θ = h / r, θ = tan-1 (h / r)

Where, h = height of the powder cone.

r = radius of the powder cone.

Bulk density:

Both loose bulk density (Db) and tapped bulk density (Dt) was determined. A quantity of 2 gm of granules from each formula, previously shaken to break any agglomerates formed, was introduced in to 10 ml measuring cylinder. After that the initial volume was noted and the cylinder was allowed to fall under its own weight on to a hard surface from the height of 2.5 cm at 2 second intervals. Tapping was continued until no further change in volume was noted. Db and Dt were calculated using as the following equations.

Db = Weight of the granules /Untapped Volume of the packing

Dt =Weight of the granules /Tapped Volume of the packing

Compressibility index:

The Compressibility Index of the granules was determined by Carr’s (compressibility) index. It is a simple test to evaluate the Dt and Db of a granules and the rate at which it packed down. The formula for Carr’s Index is as below

I = Dt – Db X 100

Where, Dt is the tapped density of the powder, Db is the bulk density of the powder

Hausner’s ratio:

Hausner’s ratio is an index of ease of powder flow; it is calculated by following formula.

Hausner ratio = Dt / Db

Total porosity:

Total porosity was determined by measuring the volume occupied by a selected weight of a granule (V bulk) and the true volume of the granule (The space occupied by the powder exclusive of spaces greater than the intermolecular spaces).

Porosity (%) = V bulk - V x100

V bulk

Evaluation of diclofenac sodium matrix tablets:

The prepared tablets were evaluated for general appearance, content uniformity, hardness, friability, weight variation, thickness, diameter, disintegration time and in vitro dissolution profile using methods specified in Indian Pharmacopoeia. The following evaluation tests were carried out on formulated tablets which includes;

i) General appearance:

The morphological characterization which includes size, shape, colour, presence or absence of odour, taste surface texture of the tablets was determined.

ii) Thickness & diameter:

Five tablets were picked from each formulation randomly and thickness and diameter was measured individually. It is expressed in mm and standard deviation was also calculated. The tablet thickness and diameter was measured using Vernier caliper.

iii) Hardness:

Hardness indicates the ability of a tablet to withstand mechanical shocks while handling. The hardness of the tablets was determined using Monsanto hardness tester.

It is expressed in kg/cm2. Five tablets were randomly picked and hardness of the same tablets from each formulation was determined. The mean and standard deviation values were also calculated.

iv) Friability test:

Friability test is performed to assess the effect of friction and shocks, which may often cause tablet to chip, cap or break. Roche Friabilator was used for the purpose. Pre weighed sample of ten tablets were placed in the Friabilator, which was then operated at 25 rpm for 4 minutes or ran up to 100 revolutions. After 100 revolutions the tablets were dusted and reweighed. Compressed tablets should not lose more than 1% of their weight.

The % friability was then calculated by the following formula:

Percentage friability =

(Initial weight - Final weight /Initial weight) × 100

V) Drug content:

Five tablets were weighed individually and powdered. The powder equivalent to average weight of tablets was weighed and drug was extracted in Phosphate buffer pH 6.8, the drug content was determined measuring the absorbance at 276 nm after suitable dilution using a Shimadzu UV- Vis double beam spectrophotometer 1601.

vi) In vitro disintegration time:

In vitro disintegration time was performed by apparatus specified in USP at 50 rpm. Phosphate buffer pH 6.8, 900 ml was used as disintegration medium, and the temperature of which was maintained at 37±2°C and the time in second taken for complete disintegration of the tablet with no palpable mass remaining in the apparatus was measured in seconds.

vii) Swelling index:

The extent of swelling was measured in terms of % weight gain by the tablet. The swelling behavior of all formulation was studied. One tablet from each formulation was kept in a Petri dish containing pH 6.8 phosphate buffers. At the end of 2, 4, 6, 8 10 and 12 hrs tablets were withdrawn, soaked on tissue paper and weighed and then

viii) In vitro drug release studies:

In vitro release studies were carried out using tablet dissolution test apparatus USP

XXIII. Two objectives in the development of in vitro dissolution tests are to show (1) that the release of the drug from the tablet is as close as possible to 100% and (2) that the rate of drug release is uniform batch to batch and is the same as the release rate from those batches proven to be bioavailable and clinically effective.

The following procedure was employed throughout the study to determine the in vitro dissolution rate for all the formulations.

Drug release study was carried out by using USP dissolution rate test apparatus-II (Electro lab, Mumbai, India). The study was conducted at 37°C and 50 rpm in 900 ml pH 6.8-phosphate buffer and studied for drug release up to 12 h. Five ml of sample was withdrawn at different time intervals, filtered and the drug content was estimated at 276 nm after suitable dilution.

ix) Data Analysis:

To examine the drug release kinetics and mechanism, the cumulative release data were fitted to models representing zero order (Q v/s t), first order [Log(Q0-Q) v/s t], Higuchi’s square root of time (Q v/s t_1/2 ) and Peppas double log plot (log Q v/s log t) respectively, where Q is the cumulative percentage of drug released at time t and (Q₀-Q) is the cumulative percentage of drug remaining after time t. In short, the results obtained from in vitro release studies were plotted in four kinetics models of data treatment as follows:

 Cumulative percentage drug release Vs. Time (zero order rate kinetics)

 Log cumulative percentage drug retained Vs. Time (first order rate kinetics)

 Cumulative percentage drug release Vs. √T (Higuchi’s classical diffusion equation)

 Log of cumulative percentage drug release Vs. log Time (Peppas exponential equation)

x) Scanning Electron Microscopy

The optimized formulation (F5) was selected for Scanning Electron Microscopy (SEM) analysis. The tablet surface morphology was studied at zero time and 12th hour of dissolution. The morphological characters of these 2 scans were compared to hypothesize the mechanism of drug release and swelling.

xi) Stability Studies:

Stability of a drug has been defined as the ability of a particular formulation, in a specific container, to remain within its physical, chemical, therapeutic and toxicological specifications.

The purpose of stability testing is to provide evidence on how the quality of a drug substance or drug product varies with time under the influence of a variety of environmental factors such as temperature, humidity and light, and enables recommended storage conditions, re-test periods and shelf lives to be established.

ICH specifies the length of study and storage conditions:

Long term testing 25⁰C±2⁰C/60% ±5% RH for 12 months

Accelerated testing 40⁰C±2⁰C/75% ±5% RH for 6 months

In the present study, stability studies were carried out at 40⁰C±2⁰C/75%±5% RH for a period of 90 days for the selected formulations. The formulations were then evaluated for changes in the physicochemical properties, in vitro disintegration time, swelling study and in vitro drug release.

RESULTS AND DISCUSSION:

The powdered dry water soluble mucilage was extracted from leaves of Basella alba plant for pharmaceutical use. The standard procedure was used to isolate mucilage and where purified by using water as solvent and acetone as non-solvent. The total yield of mucilage by acetone precipitation method was found to be 14.5%.

Additives play an important role in pharmaceutical preparations like tablet, lotions, suspensions, syrups and ointments. Recent trends towards the use of the vegetable and nontoxic products demand the replacement of synthetic excipients with natural ones. Vegetable gums provide appropriate solution to the current problem. Hydrophilic matrices are an interesting option when developing an oral sustained release formulation. The drug release from such matrices can be controlled through their physical properties. Polysaccharides are the choice of materials among the hydrophilic polymers used, because they are nontoxic and acceptable by the regulating authorities. In view of the easy availability of the Basella alba leaf mucilage, the mucilage from the Basella alba leaf mucilage was investigated for its application as a release retardant in diclofenac sodium matrix tablet. The mucilage was extracted using solvents such as distilled/demineralized water, hot water, PBS pH 4.0, pH 6.8 and pH 9.2 and the yield of the dry water soluble mucilage was varied depends upon the solvents used. Percent yield of the dry water soluble mucilage was 45%, 60%, 22%, 30% and 35% in distilled/demineralized water, hot water, PBS pH 4.0, PBS pH 6.8, and PBS pH 9.2 respectively. The solvents like distilled/demineralized water, hot water and phosphate buffer pH 9.2 could be used for extraction for better yield.

Drug-Excipients Compatibility Studies:

Fourier transform infrared (FTIR) analysis

Physical mixture of diclofenac and formulative ingredients were subjected for IR spectroscopic analysis to ascertain whether there was any interaction between drug and excipients used. The IR spectra’s showed similar characteristic peaks at their respective wavelengths with minor differences. The similarity in the peaks indicated the compatibility of drug with formulation excipients. IR spectra of the physical mixture of drug with formulative ingredients were depicted in figure 1, 2, and 3.

Table 2: Pre compression evaluation of diclofenac sodium granules

Form-ula-tions	Angle of repose()*	Bulk density (gm/cm³)*	Tapped density (gm/cm³)*	Carr’s index (%)*	Hausner ratio (H_R)*	Bulkiness (cc/g)*	Flow-abili-ty	Total porosity	Drug Content (%)
F1	24.11±0.07	0.421±0.03	0.481±0.07	12.47±0.02	1.143±0.05	2.375	Good	26.92±0.06	95.53±0.02
F2	21.84±0.03	0.312±0.02	0.364±0.01	14.28±0.01	1.167±0.01	3.205	Good	31.42±0.01	95.64±0.04
F3	22.73±0.04	0.407±0.05	0.485±0.05	16.08±0.02	1.192±0.01	2.457	Good	27.2±0.02	95.62±0.03
F4	23.97±0.08	0.267±0.02	0.30±0.03	11.29±0.02	1.124±0.03	3.745	Good	33.09±0.07	96.4±0.01
F5	23.91±0.01	0.338±0.07	0.385±0.02	21.20±0.03	1.139±0.04	2.958	Good	28.43±0.03	98.14±0.05
F6	24.68±0.02	0.39±0.03	0.44±0.06	11.01±0.03	1.128±0.05	2.564	Good	34.25±0.03	97.86±0.06

*All values are expressed as mean ± SD, n=3.

Table 3: Results of evaluation of diclofenac sodium matrix tablets

Formulation code	Thickness (mm)*	Diameter (mm)*	Hardness (kg/cm²)*	Friability (%)**	Drug content (%)*	Weight variation (mg)***	Appearance
F1	3.60±0.04	8.01±0.01	6.0±0.16	0.55±0.02	99.5±0.05	250±0.01	++
F2	3.67±0.03	8.01±0.04	5.6±0.08	0.35±0.03	99.0±0.01	251±0.02	+++
F3	3.61±0.04	8.02±0.02	4.5±0.21	0.25±0.01	98.5±0.02	251±0.04	+
F4	3.67±0.04	8.01±0.02	5.0±0.11	0.30±0.06	98.0±0.01	249±0.05	++
F5	3.62±0.02	8.01±0.03	6.5±0.09	0.21±0.03	98.0±0.01	250±0.03
F6	3.62±0.03	8.03±0.02	5.5±0.12	0.45±0.04	99.0±0.01	252±0.04	+++

*All values are expressed as mean ± SE, n=5; **All values are expressed as mean ± SE, n=10; ***

All values are expressed as mean ± SE, n=20; += Average; ++= good, +++= excellent

Evaluation of diclofenac sodium matrix tablets

The tablets of different formulations were subjected to various evaluation tests. The shape of the tablets of all formulations remained off white, smooth, flat faced circular with no visible cracks. The thickness and diameter of formulated matrix tablets was ranged from 3.60±0.04 to 3.67±0.04 mm and 8.01±0.01 to 8.03±0.02 respectively. The values are almost uniform in all formulations. In a weight variation test, the Pharmacopoeial limit for the percentage deviation for the tablets of more than 250mg is ± 5%. The average percentage deviation of all tablet formulations was found to be within the above limit, it was found to be form 249±0.05 mg to 252±0.04 mg. and hence all formulations passed the test for uniformity of weight as per official requirements. The content uniformity test was performed for all the six formulations and drug content in the formulated tablets was ranged from 98.0±0.01 to 99.5±0.05. The results indicated that drug content was found to be uniform among different batches of the tablets. The hardness of the tablets of all batches ranged from 4.5±0.21 to 6.5±0.09 kg/cm2. It can be observed from results that the increase in the concentration of mucilage in the tablet resulted in a corresponding increase in the hardness of tablets, which may be attributed to the plastic nature of mucilage and also due to presence of higher concentration of mucilage, which is generally responsible for more hardness of the tablet. In the present study, the percentage friability for all the formulations was below 1% indicating that the friability is within the prescribed limits. The formulated tablets were found to have good hardness and minimal weight loss on friability indicates that the tablets can with stand the mechanical shocks during their handling and transport. Formulations F1 and F2 were found disintegrated within 45 minutes of dissolution testing in pH 1.2 buffers whereas formulation F3-F6 were found to retain their shape for up to 12 hours of dissolution testing (table 3).

Swelling Behavior of diclofenac matrix tablets:

Since the rate of swelling is related and may affect the mechanism and kinetics of drug release, the penetration of the dissolution medium and swelling of tablets were determined. The extent of swelling was measured in terms of percentage weight gain by the tablets. The swelling behavior of all the formulations was studied. The swelling index was calculated with respect to time. As time increases, the swelling index was increased, because weight gain by tablet was increased proportionally with rate of hydration up to 6 h. Later on, it decreases gradually due to dissolution of outermost gelled layer of tablet into dissolution medium. The results of swelling studies show that, as the proportion of mucilage in the tablets was increased, the percent swelling increased, and the percent erosion decreased. Similar results were earlier reported for mucilage of Hibiscus rosasinensis matrix tablets formulated using pure mucilage showed greater swelling as compared with the matrix tablets containing mucilage and drug. The release of drug from hydrophilic matrices occurs as a result of complex interaction between diffusion, dissolution, and erosion mechanisms. On coming in contact with water, hydrophilic matrices undergo gel formation, and progressive phase transition from glassy to rubbery state takes place. This results in solvation of individual polymer chains. As the swelling continues, the swollen matrix retains more water until the shear forces in the dissolution medium disentangle the individual polymer chains from the matrix. It has been observed that the cumulative percent drug release decreases with increasing concentration of mucilage and swelling index (figure 6).

In vitro Drug Release Study:

The in vitro drug release characteristics were studied in simulated gastric and intestinal fluids for a period of 12 hours using USP XXIII dissolution apparatus 2 (paddle type at 50 rpm). Release of the drug from the matrix-tablet comprising drug, and hydrophilic polymer, the release should follow three steps. First step is the penetration of the dissolution medium in the tablet matrix (hydration). Second step is the swelling with concomitant or subsequent dissolution or erosion of the matrix and third step is the transport of the dissolved drug, either through the hydrated matrix or from the parts of the eroded tablet, to the surrounding dissolution medium.

The results show that less amount of the drug dissolved during the first 2 h in 0.1 N HCl. Diclofenac sodium is a weakly acidic drug with pKa of 4.2; as a result, it is practically insoluble in acidic solution. Thus, the lower solubility of Diclofenac sodium in 0.1 N HCl accounted for <1% release of the drug. Sustained, but complete drug release was displayed by all formulations in phosphate buffer (pH 6.8). Thus it can be concluded, that drug dissolution was a function of drug solubility, at various pH ranges. Indeed, pH dependent solubility of diclofenac is well known. It can be observed from the results that, as the proportion of mucilage in tablets was increased there was a decrease in the release rate. The results of dissolution studies indicated that F1, F2, and F3 released 34%, 24%, and 20% of diclofenac at the end of 2 hours; and 96%, 93%, and 92 % of drug at the end of 8 hours, 9 hours, and 10 hours, respectively. The high dissolution rate observed with F1 could be due to its low swell ability, indicated by lower viscosity values and lower concentration of mucilage.

The release of drug depends not only on the nature of matrix but also upon the concentration of mucilage. This may be due to changes in the structural reorganization tortuosity or gel strength of hydrophilic gum polymers. Failure to generate a uniform and coherent gel may cause rapid drug release. The Formulation F5 showed a slow and complete drug release of 98% over a period of 12 hr. The results of in vitro studies indicated that the rate and extent of drug release were decreased significantly with an increase in BAM concentration, which may be attributed to increase in the polymer matrix, gel strength and to the formation of gel layer with longer path of diffusion, resulting in reduction of diffusion coefficient of the drug. When the BFM matrix tablets of diclofenac come into contact with the dissolution medium, they take up water and swell, forming a gel layer around the matrix. Then the dissolved drug diffuses out of the swollen BAM matrix at a rate determined by the amount and viscosity of BAM in the tablet formulation. Lactose is the most useful filler used for tablet formulations. It is water-soluble and would modify the drug release for undergoing dissolution. Lactose in aqueous solution plays a major role as important physical barrier, affecting the release kinetics, by reducing the tortuosity of diffusion pattern of the drug. The results indicated retardant release of drug from all the formulations with increase in the BAM concentration. Formulation containing 12.5%w/w concentration of the BAM showed slow and sustained release of the diclofenac over a period of 12 h. From the results it suggests that the nature of excipient used appeared to play a minor role in regulating the release, while the mucilage content was a major factor. Lower mucilage content would result reduced swelling with corresponding decrease in diffusional path length.

Moreover the excipient would either enhance dissolution or erosion mechanism, depending on the solubility of the excipient, which compensates for the slowing diffusion rate through the gradually increasing gel layer by creating greater porosity for the drug pathway. F6 give 70% drug release in 12 hours and which indicate that % of guar gum used in the formulation it sustained the drug release but the results were not satisfactory.

From the findings, obtained so far it can be concluded that BAM in the concentration of 12.5%w/w (F5) was promising concentration for oral controlled release tablet of diclofenac which showed slow and sustained release of the diclofenac over a period of 12 h. Hence F5 is considered as the optimized batch. In vitro drug release profile of optimized batch F5 and the commercial sustained-release tablet of diclofenac sodium (Voveran SR sodium) were compared; the results indicated that formulation F5 gave the release profile close to the marketed product. Comparative drug release profile from different batches of diclofenac matrix tablet. The comparative release rate pattern of diclofenac from various batches of formulated tablets and marketed tablet is shown in Figure 7.

Scanning Electron Microscopy

The surface morphology of optimized formulation (F5) at zero time and at 12th hour of dissolution study was observed. SEM photographs before dissolution it showed intact surface without any perforations, channels, or troughs. After dissolution, the solvent front enters the matrix and moves slowly toward the center of the tablet. The drug diffuses out of the matrix after it comes in contact with dissolution medium. The images of the tablet showed the presence of both gelling structures and pores on the surface. Thus, the presence of both pores and gelling structure indicates the combination of diffusion and erosion mechanism in the release of diclofenac from the matrix tablet of batch F5. The SEM photographs of diclofenac matrix tablet (F5) were shown in Figure 8.

At zero time of dissolution study At 12^th hour of dissolution study

Figure 8: SEM photomicrographs of optimized batch of diclofenac matrix tablet (F5)

Mechanism of drug release:

To determine the mechanism of drug release kinetics from optimized formulation F5, the dissolution data were treated according to Higuchi (cumulative percentage of drug released vs. square root of time), Korsmeyer-Peppas model (log cumulative percentage of drug released vs. log time) equations and Hixson-Crowell model (cube root % drug remaining vs time) along with zero order (cumulative amount of drug released vs. time) pattern. The data were processed for regression analysis using MS EXCEL statistical function. It can be observed from the results that the release rate data of optimized formulation of diclofenac sodium matrix tablets F5 formulated using mucilage as the matrix did not follow a zero-order release pattern. By using Higuchi’s kinetics or square-root kinetics this would explain why drug diffuses at a comparatively slower rate as the distance of diffusion increases. In our experiments, the in-vitro release profiles of drug from optimized formulation F5 could be best expressed by Higuchi’s equation, as the plots showed high linearity (R2= 0.9908). To confirm the diffusion mechanism, the data were fit into Korsmeyer-Peppas model. The optimized formulation F5 showed high linearity (R2= 0.9907, with slope (n) values 0.6661, this (n) value indicating that coupling of diffusion and erosion mechanism so called anomalous non-Fickian diffusion and may indicate that the drug release is controlled by more than one mechanism, which indicate that formulation F5 release the drug by diffusion coupled with erosion mechanism. Hixson-Crowell plots showed linearity (R2= 0.9867) indicated a change in surface area and diameter of the tablet with the progressive dissolution of the matrix as a function of time. The result of modeling and drug release kinetics of optimized diclofenac sodium matrix tablet Batch F5 were shown in table 4 and in figure 9-12.

CONCLUSION:

Nature has provided us a wide variety of materials to help, improve and sustain the health of all living things either directly or indirectly. In recent years there have been important developments in different dosage forms for existing and newly designed drugs and natural products, and semi-synthetic as well as synthetic excipients often need to be used for a variety of purposes. Gums and mucilage’s are widely used natural materials for conventional and novel dosage forms. These natural materials have advantages over synthetic ones since they are chemically inert, nontoxic, less expensive, biodegradable and widely available. They can also be modified in different ways to obtain tailor-made materials for drug delivery systems and thus can compete with the available synthetic excipients. Basella alba is a wildly cultivated, cool season vegetable with climbing growth habit. Malabar spinach is high in vitamin A, vitamin C, iron and calcium. It is low in calories by volume, but high in protein per calorie. The succulent mucilage is a particularly rich source of soluble fiber. Literature survey reveals that comprehensive physicochemical characterization and exploration of BAM as versatile pharmaceutical excipients in pharmaceutical formulations has not been done. Hence, the present study is aimed to enhance the use of BAM as a natural plant based excipients to develop various pharmaceutical formulations and it will encourage cultivation and use of this mucilage in the pharmaceutical industry. In the present work, an attempt was made to develop matrix tablets of diclofenac using natural release retardant polymer isolated from Basella alba leaves and its efficiency was compared with most widely used natural release retardant polymer like guar gum.

ACKNOWLEDGEMENTS:

The authors are thankful to the Management and Principal of Karavali college of Pharmacy, Mangalore for providing all the facilities to conduct the research work and the authors are also thankful to BPRL, Bangalore, India for generous gift sample of diclofenac.

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Received on 12.02.2016 Modified on 15.03.2016

Res. J. Pharm. Dosage Form. and Tech. 2016; 8(2):81-94.

DOI: 10.5958/0975-4377.2016.00012.4

Parameters	Before stability studies	After stability studies
Physical appearance	Off white, smooth, flat faced	Off white, smooth, flat faced
Weight variation(mg)	250±0.03	250±0.03
Hardness (kg/cm²)	6.5±0.09	6.4±0.09
Friability (%)	0.21±0.03	0.20±0.03
Drug content (%)	98.0±0.01	97.8±0.01
In vitro release (%) 12 h.	98.00	97.5