Development and Evaluation of Floating Microspheres of Sumatriptan Succinate using Ethyl Cellulose and Mucilage Extracted from Vigna Mungo

Aim: The present investigation is to formulate and evaluate gastroretentive floating microspheres for sumatriptan succinate. Gastric retention is widely used approach to retain dosage form in stomach and to enhance absorption of drugs. Methods: The gastroretentive floating microspheres was prepared by two different techniques as solvent evaporation and W/O/W multiple emulsion technique. Ethyl cellulose, HPMC K4M polymer and mucilage extracted from Vigna Mungo in various proportions were used for formulation of microspheres. Combination of ethyl acetate and acetone in different proportion was used as organic phase and the microspheres were characterized for particle size, shape, morphology, percentage yield, entrapment efficiency, drug loading, In-Vitro Floating/Buoyancy study, In-vitro Floating/Buoyancy study and release kinetics. Results: The average particle size of all batches was found in the range 100 to 210 μm and the entrapment efficiency of all formulations was found in the range of 17.46 % to 59.28 %.Total Original Research Article Kulkarni et al.; JPRI, 33(43A): 24-36, 2021; Article no.JPRI.73510 25 floating time for Sumatriptan succinate floating microspheres was observed more than 12 h. The InVitro drug release study was performed for all formulations showed drug release in controlled manner. Conclusion: The particle size was increased with increased polymer concentration and it showed that polymer concentration has an impact on the entrapment efficiency. Ethyl cellulose microspheres showed more entrapment and sustained delivery of sumatriptan Succinate than microspheres prepared by combination of Ethyl cellulose: HPMC K4M and Ethyl cellulose: Vigna mungo mucilage.


INTRODUCTION
Oral drug delivery system is the most prominent and highly acceptable route of administration. Gastroretentive drug delivery system (GRDDs) is the most feasible controlled release system in which the drug delivery is prolonged by increasing gastric residence time. By increasing gastric residence time better control is achieved on fluctuation of plasma drug concentration. Floating drug delivery system is the hydrodynamically balanced system. As dosage form has low density which allows the system to remain buoyant for prolonged duration of time in gastric fluid and it is advantageous over immediate release system including the minimization of fluctuations and act for prolonged period of time [1,2]. Floating system is divided into two main types, one is effervescent system and other is non effervescent system. For floating dosage, form desirable drugs are absorbed from stomach, having local action in stomach, poorly absorbed from alkaline pH, rapid absorption from GIT [1,2]. Sumatriptan succinate; selective agonist of 5 hydroxytriptamine, is a main choice of drug for migraine treatment. Sumatriptan succinate is effective in migraine attack in 70% of cases as well as used for treating headache, pain and other symptoms. Sumatriptan succinate does not cross blood brain barrier and has biological half life of 2.5 hr and its reported bioavailability is approximately 15% [3,4,5]. The Vigna Mungo mucilage has been used as binder, release retardant material in the development of dosage form. Vigna Mungo mucilage as a polysaccharide has excellent swelling capacity. So considering these advantages the work is initiated to develop microspheres containing Vigna Mungo mucilage. The main objective of the work is to develop microspheres as floating drug delivery as drug is rapidly and incompletely absorbed from gastrointestinal track. The drug has absorption from the stomach and upper part of small intestine [5][6][7][8]. Sustained release dosage form is mainly for better effect and longer duration of time. To allow absorption from stomach and upper part of small intestine, Sumatriptan succinate needs to be developed as Gastroretentive drug delivery system.

Materials
Sumatriptan succinate was a gift sample from Emcure Pharmaceuticals, Pune. Hydroxy propyl methyl cellulose (K4M) was received as Gift sample from Colorcon India Ltd., Goa, India. Ethyl cellulose, calcium chloride, PVA was purchased from Research Lab fine Chem. Industries, Mumbai-400002, (India). Urad dal was purchased from local market of Pune, Maharashtra, India.

Solubility estimation of sumatriptan succinate
Sumatriptan Succinate (50 mg) was added to 50 ml of distilled water, acidic buffer pH 1.2, Phosphate buffer pH 6.8 and Phosphate buffer pH 7.4, respectively. The solutions were kept for stirring on mechanical shaker for 2 hrs at room temperature and the solutions were filtered by using 0.22 µ Whatman filter paper. Suitable dilutions were made and absorbance of final solutions was recorded using UV spectrophotometer at λmax 282 nm.

Isolation/ extraction of mucilage [9-13]
Urad dal (Vigna Mungo) Mucilage was isolated from freshly dried, coarsely powdered and dehusked seeds of Vigna Mungo. 20 g of Seed powder of Vigna Mungo was taken and added into 200 ml of cold distilled water. Slurry was prepared and then was poured into 800 ml of boiling distilled water. The solution was boiled for 20 min in water bath under constant stirring. The resulting solution was kept overnight, so that most proteins and fibres settled down. The material was squeezed by using muslin bag to remove mark from filtrate and the filtrates were poured into twice volume of absolute ethanol with continuous stirring to precipitate mucilage. The mucilage was separated, collected and dried in an oven at 50°C for 24 hrs and the dried mucilage was powdered and passed through 40# sieve.

Preparation of floating microspheres by solvent evaporation methods [14-19]
Sumatriptan Succinate microspheres were prepared by varying the concentration of polymers in the formulation. The Ethyl acetate and acetone in various ratios in various ratios was used as organic phase and in aqueous phase comprises distilled water with emulsifier Tween 80. The composition of batches was given in

Particle size, shape and morphology
The formed microspheres were characterized by optical microscopy for determination of particle size and size distribution. The eyepiece microscope was calibrated with stage micrometer.
Randomly measured 100 microspheres and average particle size calculated. Edmondsons equation was applied.
dmean= Ʃnd/ Ʃn Where, n = the number of counted microspheres and d = mean size range

Percentage yield
Percentage yield of microspheres calculated by the using the formula % Yield= Total weight of microspheres/ total weight of polymer and drug *100

Drug Entrapment efficiency and drug loading
The percent of drug encapsulated into the formulation is determined by drug entrapment efficiency method. The weighed amount of microspheres equivalent to 20 mg drug was crushed in the mortar and pestle. Then it was dissolved in methanol. The resultant solution was filtered by 0.22 µ Whatman filter paper. After suitable dilution the absorbance was measured at 282 nm by UV Spectrophotometer. The entrapment efficiency and drug loading were calculated by using following formula.
% Entrapment Efficiency = Practical amount of drug content/ Total theoretical amount of drug content *100 % Drug loading = Actual drug content/ Weight of microspheres *100

Micromeritics study
To determine flow properties of microspheres, the micromeritic properties of microspheres such as bulk density, tapped density, angle of repose; compressibility index and Hausners ratio were performed.

Solubility Studies
Solubility study of Sumatriptan succinate showed that drug is freely soluble in water, soluble in Phosphate Buffer pH 7.4, acid buffer pH 1.2, and Phosphate Buffer pH 6.8.

Phytochemical testing
The phytochemical testing of extracted Vigna Mungo mucilage through Molish test, Iodine test and Ruthenium red test confirms the extracted material/ mucilage was polysaccharide (Table 5 and Fig. 1).

Flow properties
Flow property of extracted mucilage was found to good as it is confirmed by estimation by estimation of angle of repose, bulk density, tapped density and Compressibility index (Table 7).

Evaluation of Sumatriptan Succinate Floating Microspheres
Flow properties of Sumatriptan succinate floating microspheres: Bulk density of all formulations was found in the range of 0.434 to 0.740 g/cm 3 . Tapped density of all formulations was in the range of 0.520 to 0.804 g/cm 3 . It shows microspheres have low density than gastric fluid. (Density of gastric fluid is 1.064 g/cm 3 ). It is better for floating ability. Compressibility index is in the range of 7.7 % to 22.5 %. Hausners ratio of microspheres was in the range of 1.08 to 1.29. Formulated microspheres showed angle of repose was in the range of 25 ͦ to 35 ͦ and it showed good flowing property.

Particle size and percentage yield
Microspheres particle size and shape studied by optical microscopy. Particles were uniformly distributed and spherical round in shape. The average particle size of all batches was found in the range 100 to 210 μm. The mean particle size of the microspheres was found to be increasing with increasing polymer concentration. The viscosity of the medium increased at higher polymer concentrations resulting in increased interfacial tension. Shearing efficiency decreased due to increased viscosity and thus particle size was increased with increased polymer concentration.
Percentage yield of different formulation batches in the range of 47.00 % to 87.88 %. Drug to polymer ratio 1:1 showed less percentage yield. As drug polymer ratio increased percentage yield is increased. This result showed that by increasing polymer concentration percentage weight increased. 800 to 1000 RPM is the optimum stirring speed of triple blade stirrer.

Entrapment efficiency and drug loading
The drug entrapment efficiency of microspheres varied from 17.46 % to 59.28 %. Result showed that as polymer concentration increased the entrapment efficiency get increased due to the higher polymer content, drug gets more surrounded by the polymer, thus polymer coating on drug increased and encapsulation of drug increased. The increased drug entrapment efficiency is attributed because of increased ethyl cellulose concentration. Microsphere batches prepared by Ethyl cellulose with HPMC K4M resulted decreased drug entrapment efficiency and drug loading. As HPMCK4M is hydrophilic polymer, it swells and erodes with time. HPMC could facilitate the diffusion of an entrapped drug to the surrounding aqueous medium during preparation of microspheres. So it cause decrease in entrapment of drug. Similar results were observed for the microspheres prepared by combination of polymer (ethyl cellulose) with Vigna Mungo mucilage. It is also attributed to water solubility of extracted mucilage. Entrapment efficiency is depending upon nature of drug, drug solubility, nature of polymer, polymer solubility, affinity between drug and polymer. Sumatriptan Succinate is hydrophilic drug, so aqueous solubility is more. During the microspheres preparation the drug diffusion in the aqueous medium was more. Leaching of drug to the external aqueous medium, which caused decrease in entrapment efficiency of Sumatriptan Succinate floating microspheres.
To overcome this problem, batch no. 18 to 21 prepared by multiple emulsion method. In this external aqueous medium was 0.5 % PVA solution with 10 % Calcium chloride. It was observed that there was no effective increase in entrapment and drug loading. Batch no. 22 and 23 contains combination of drug and ethyl cellulose in the ratio of 1:6 and 1:9 respectively. These microspheres prepared by w/o/w multiple emulsion method. As polymer concentration is more and primary aqueous medium W1 is less in amount, drug diffusion is less and encapsulation is more. Therefore batch no. 22 and 23 showed highest encapsulation efficiency.

Percentage buoyancy and total floating time
Buoyancy or floating ability of microspheres depends upon the apparent density and nature of polymer. The percentage buoyancy of all batches was above 65 %, which is studied for 12 h. The total floating time for all batches was above 12 h. This result showed good floating ability of the Sumatriptan Succinate microspheres. It is observed that with increasing polymer concentration, percentage buoyancy increased.

In-vitro dissolution study
In-vitro drug release study of microspheres batches was performed in acidic buffer 0.1 N HCl. Dissolution study performed for 6 hrs. The % drug release from formulation batch of F9, F 13 and F 17 was 53.71 %, 72.12 % and 68.22 %   Fig 4), Sumatriptan succinate: Ethyl cellulose: Vigna Mungo Mucilage (Part F Fig 3) and Sumatriptan succinate: Ethyl cellulose: HPMCK4M (Part G Fig 3) does not show any melting endotherm corresponding to the pure drug. It suggests sumatriptan succinate in microspheres was in amorphous phase as a molecular dispersion or solid solution state in polymer matrix. Found that solid microspheres were 100-1000μm in size shown in (Fig. 5 part A, B and C). Perforated spheres formed due to rapid evaporation took place during processing. The uniform stirring speed of mechanical stirrer makes the microspheres solids and spherical. During solidification process and cross linking leads to formation of voids, it may be related to mechanisms of air bubbles or entrapped fluid. Such spheres had possibility to achieve more space for interaction with dissolution media. It results in decreases in the sustained release property. The microsphere surface became smooth and non-porous, which was effective in delayed dissolution (Fig. 5 A).Furthermore, all three batches of microspheres had a regular spherical morphology (Fig. 5

CONCLUSION
The prepared microspheres were showed excellent micromeritic properties. The average particle size of all batches was found in the range 100 to 210 μm. Particle size of microspheres was changed. It is attributed with change in polymer concentration in prepared formulation batches. As polymer proportion is increased it leads to increase in particle size. The concentration of polymers has effect on the percentage yield. Drug to polymer ratio 1:1 showed less percentage yield. As the ratio of drug to polymer increased the percentage yield increased. The entrapment efficiency of all formulations was found in the range of 17.46 % to 59.28 %. The microsphere batch of Formula 9, Formula 13 and Formula F 17 showed 46.92 %, 40.19 % and 43.12 % of entrapment efficiency with corresponding drug loading of 11.68 %, 9.24% and 9.92 % respectively. More entrapment is attributed to greater proportion of polymer. Ethyl cellulose microspheres showed more entrapment than with HPMCK4M and Vigna Mungo mucilage. HPMC K4M and Vigna Mungo mucilage in microsphere formulation erodes with time. This is probable reason for less entrapment. Entrapment efficiency also depends upon of drug, drug solubility, nature of polymer, polymer solubility, affinity between drug and polymer. Sumatriptan Succinate is hydrophilic drug, so aqueous solubility is more. During the microspheres preparation the drug diffusion in the aqueous medium was more. Leaching of drug to the external aqueous medium, this resulted in poor entrapment efficiency for Sumatriptan Succinate. Entrapment efficiency was increased in W/O/W multiple emulsion method. All formulations showed good floating ability. Ethyl cellulose microspheres showed more entrapment and sustained delivery of sumatriptan Succinate than microspheres prepared by combination of Ethyl cellulose: HPMC K4M and Ethyl cellulose: Vigna mungo mucilage.

DISCLAIMER
The research was not funded by the producing company rather it was funded by personal efforts of the authors.

CONSENT
It is not applicable.

ETHICAL APPROVAL
As per international standard or university standard written ethical approval has been collected and preserved by the author(s).