Introduction
Microspheres are characteristically free flowing powders consisting of proteins or synthetic polymers or polysaccharides which are biodegradable or non-biodegradable in nature and ideally having a particle size less than 200μm.1 These vary widely in quality, sphericity, uniformity of particle and particle size distribution. This is an important approach in delivering therapeutic substance to the target site with specificity, if modified, and to maintain the desired concentration at the site of interest. Controlled drug delivery can be achieved using microspheres as they offer various alterations in their structure for drug release modifications.2 It has been observed that microspheres are better choice of drug delivery system because it is of the advantage of target specificity and better patient compliance.
In long-term therapy for the treatment of chronic disease conditions like diabetes mellitus type 2 conventional formulations are required to be administered in multiple doses and therefore have several disadvantages.3 Controlled release dosage forms have been demonstrated to improve therapeutic efficiency by maintaining a steady drug plasma concentration. The use of polymers in controlling the release of drugs has become an important tool in the formulation of pharmaceutical dosage forms.4
A promising new approach to treat type 2 diabetes mellitus is to enhance and prolong the physiological actions of the endogenous incretin hormones, glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) by inhibiting dipeptidyl peptidase IV (DPP-4), the enzyme responsible for their degradation and inactivation. Both GIP and GLP-1 have been shown to stimulate insulin release in a glucose-dependent manner.5 Vildagliptin (VG) is one of the very effective incretin enhancers that functions as a potent inhibitor of DPP-4 also due to its special incretin dependent mechanism of action it may not cause hypoglycemia even after remaining in blood for prolonged duration.6
The aim of this study was to formulate Vildagliptin loaded microspheres for controlled delivery. Developed microspheres were characterized for their size, surface morphology, entrapment efficiency and drug release. The influence of formulation variables such as stirring speed, polymer concentration, surfactant, were investigated to achieve the better formulations in order to sustain the action of Vildagliptin; enabling reduction in dosing interval for the treatment of hyperglycemia associated with T2DM.
Materials and Method
Methods
Microspheres of Vildagliptin were obtained by solvent evaporation technique. Firstly, polymer (ethylcellulose) was dissolved in dichloromethane and then the drug (Vildagliptin) were added to the above solution. The polymer drug solution so obtained was injected into the PVA solution maintained at variable speed using mechanical stirrer. Stirring was continued for required duration. The formed microspheres were collected by filtration, washed with n-Hexane and dried to obtain free flowing microspheres.
Table 1
Formulation design of vildagliptin loaded microspheres
Characterization of Microspheres
Particle size analysis
Particle sizes of microspheres were determined by optical microscopy. Optical microscope was fitted with eye piece micrometer which was then calibrated with a stage micrometer. 7 About 100 microspheres were randomly selected from each formulation and then the average size was calculated.
Surface morphology
The prepared vildagliptin microspheres were morphologically examined for shape, size surface morphology and topological properties using scanning electron microscope (FEI, Model NOVANANO 450) after gold sputtering at a pressure of 5.13E to 4 pascal and 5 KV at 00 was maintained to get the photographs.
Determination of percentage yield of microspheres
The prepared microspheres were completely dried and then weighed. The percentage yield was calculated by: 8
% Yield =
Determination of flow properties of microspheres
The prepared microspheres were evaluated for flow properties including bulk density, tapped density, Carr’s index, Hausner ratio and angle of repose. 9
Bulk density
It is the ratio of total mass of microspheres to the bulk volume of microspheres. It was measured by pouring the weighed microspheres into a measuring cylinder and the volume was noted. It is expressed in gm/ml and is given by
Bulk density =
Tapped density
It is the ratio of total mass of microspheres to the tapped volume of microspheres. The tapped volume was measured by tapping the microspheres to constant volume. It is expressed in gm/ml and is given by
Tapped density =
Carr’s Index
It indicates the ease with which a material can be induced to flow. It is expressed in percentage and is given by
Carr’s Index =
Hausner ratio
It is an indirect index of ease of flow of microspheres. It is measured by
Hausner ratio =
Angle of repose (θ)
The friction forces in a loose powder can be measured by the angle of repose (θ). It is defined as maximum angle possible between the surface of pile of powder and the horizontal plane.
The microspheres were allowed to flow through a funnel fixed to a stand at definite height. The angle of repose was then calculated by measuring the height and radius of the heap of microspheres formed. It is measured by
tanθ =
θ = tan-1
Drug entrapment efficiency
To calculate the entrapment efficiency, accurately weighed quantity of microspheres (50 mg) were taken along with 50 ml of phosphate buffer pH 7.4 in a volumetric flask and kept for 24 hours. It was then filtered, suitably diluted and then analyzed by UV spectrophotometry at 210 nm. 10
% Entrapment Efficiency =
In vitro release studies of microspheres
In-vitro release of Vildagliptin microspheres was carried out using the USP dissolution test apparatus at 37±0.50C in 900 ml of phosphate buffer pH 7.4. Microspheres equivalent to 50 mg Vildagliptin was placed in the muslin cloth and rotated at 100 rpm. A sample of 5 ml was withdrawn at various time intervals and replaced with equal amount of medium to maintain the sink condition. The withdrawn samples were analyzed by UV spectrophotometer at 210 nm using phosphate buffer 7.4 as blank solution. 11
Effect of different formulation variables on various evaluation parameters
The influences of different formulation variables on various evaluation parameters were studied. The effects of polymer concentration (Ethylcellulose 1000-1250 mg), emulsifier concentrations (PVA concentration 0.1%-0.5%), and altered stirring speed of a mechanical stirrer (200, 400, 600 rpm) on microspheres characteristics (percentage yield, drug entrapment efficiency, particle size and cumulative drug release) were studied.
Results
Table 2
Effect of formulation variables on various evaluation parameters
Table 3
Flow properties of Vildagliptin microspheres
Bulk density of all the batches was in the range of 0.63 – 0.68 gm/cm3. Tapped density in the range of 0.71 – 0.78 gm/cm3. Carr’s index in range of 10.95 – 14.86 and Hausner ratio varies from 1.07 – 1.17 indicating excellent flow properties. Angle of repose was also found in the prescribed range showing excellent flow characteristics.
Table 4
Effect of variables on various parameters
Effect of concentration of polymer
The increase in the polymer concentration equals an approximately identical increase in the particle size and entrapment efficiency. The increase in the concentration of polymer results in the decrease in the % drug release. The increased polymer concentration might have led to increased density of the polymer matrix, resulting in an increased diffusional path length and consequent retardation of drug release.
Effect of concentration of PVA
The increase in the PVA concentration equals an approximately identical increase in the entrapment efficiency. The particle size was dependent on the external phase viscosity, as the increasing concentration decreased the particle size. Increased PVA concentration ensured better system stabilization against coalescence of the emulsion and therefore led to formation of smaller microspheres. The increase in the concentration of PVA results in the decrease in the % drug release. All the formulations prepared at 0.1% concentration exhibited maximum drug release than the formulations prepared with 0.3% and 0.5%. This could be probably due to increasing viscosity of the external phase. 12
Effect of stirring speed
The increase in the stirring speed equals an approximately identical decrease in the entrapment efficiency. Increasing the stirring speed delivers greater energy to the system, resulting in an increased breakdown of the forming microspheres and lower entrapment efficiency. The results confirmed that the microsphere mean size decreased with an increase in the stirring speed. The force of higher stirring distributes the internal phase into smaller droplets, resulting in the formation of smaller sized microspheres. The increase in the stirring rate results in the identical increase in the % drug release.13
Conclusion
The Vildagliptin microspheres were formed successfully by solvent evaporation technique using ethyl cellulose as a polymer, in presence of polyvinyl alcohol as surfactant. Due to the sustained property of polymer and surfactant property of polyvinyl alcohol, formulated microspheres can result in controlled release of drug.
Thus, as the rpm increases, particle size decreases, results in decrease entrapment efficiency and increases the release rate. As the PVA concentration increases, particle size decreases, resulting in decrease of entrapment and release. Hence the present work suggest that, Vildagliptin which has the lower half life and eliminates quickly from the body, when loaded with ethyl cellulose in form of microspheres results in controlled release of drug in diabetes.
Acknowledgment
We would like to thank the DAVV UGC Consortium, Indore for providing us with the scanning electron microscopy (SEM), and UV visible spectroscopy facility. Also, we wish to acknowledge the help rendered by Dr. Masheer Ahmed Khan (Lecturer, Stage-II) and Dr. Jitendra Sainy (Lecturer, Stage) of the school of pharmacy, DAVV, Indore for guiding us with our research work.