Formulation and in vitro Evaluation of Lacosamide Microspheres

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Introduction

Epilepsy is a chronic neurological disorder characterized by recurrent, unprovoked seizures resulting from abnormal and excessive neuronal activity in the brain. Lacosamide is a functionalized amino acid derivative used as an antiepileptic drug for the treatment of partial-onset seizures.[1] Microspheres are multiparticulate drug delivery systems consisting of small spherical particles in which the drug is dispersed, entrapped, or encapsulated within a polymeric matrix. [2] They generally range from a few micrometers to several hundred micrometers in size and offer several advantages over conventional single-unit dosage forms. [3] Microspheres can provide controlled drug release, improve drug stability, reduce dosing frequency, and minimize fluctuations in plasma drug concentrations. Furthermore, their relatively large surface area and multiparticulate nature may facilitate more uniform distribution within the gastrointestinal tract and reduce the risk of dose dumping associated with some single-unit sustained-release systems. [4] The incorporation of lacosamide into a polymeric microsphere system therefore represents a promising strategy for developing a controlled-release oral dosage form. Such a formulation may prolong drug release, potentially decrease dosing frequency, and provide improved control of drug exposure compared with conventional immediate-release formulations. [5] Accordingly, the present research was undertaken with the objective of formulating and in-vitro evaluating lacosamide-loaded microspheres, with particular emphasis on optimizing the formulation variables and assessing their physicochemical characteristics, drug entrapment, and in-vitro drug-release behavior. The optimized microsphere formulation may provide a useful platform for achieving sustained delivery of lacosamide and improving the overall performance of antiepileptic therapy. [6]

Materials Lacosamide was procured from Hetero Labs, HYD, Eudragit RS and Ethyl cellulose was obtained from Synpharma Research Labs, Hyderabad. Other chemicals and the reagents used were of analytical grade.

Methodology

Formulation Table Table 1: Formulation development of microspheres F. no Drug Ethyl cellulose(mg) Eudragit RS 100(mg) Polyvinyl alcohol (ml) Dichloromethane: Ethanol (1:1) Water Solvent Evaporation Technique[7]

1. Preparation of Internal Phase

• Accurately weigh the required quantity of Lacosamide and Polymer. • Dissolve polymer in a mixture of dichloromethane and ethanol (1:1). • Add Lacosamide to the polymer solution and stir until a homogeneous solution is obtained.

2. Preparation of External Phase

• Prepare 100 mL of 1% w/v Polyvinyl Alcohol (PVA) solution in distilled water. • Stir continuously to obtain a clear solution.

3. Emulsification

• Add the drug-polymer solution slowly into the PVA solution under mechanical stirring at 1000–1200 rpm. • Continue stirring for 2–3 hours at room temperature to form an oil-in-water (O/W) emulsion.

4. Solvent Evaporation

• Continuous stirring facilitates evaporation of the organic solvent. • As the solvent evaporates, polymer precipitates around the drug forming microspheres.

5. Collection of Microspheres

• Separate the formed microspheres by filtration. • Wash repeatedly with distilled water to remove residual PVA and unentrapped drug.

6. Drying

• Dry the microspheres at room temperature for 24 hours or in a hot-air oven at 40°C until constant weight is achieved.

7. Storage

• Store the dried microspheres in a desiccator until further evaluation Evaluation of Microspheres Percentage Yield The percentage yield of the prepared microspheres was determined to evaluate the efficiency of the production process. After preparation, the microspheres were collected, washed thoroughly to remove any unentrapped drug or residual solvent, and dried to a constant weight. The dried microspheres were then accurately weighed. The practical yield obtained was compared with the total weight of the drug and polymer initially used in the formulation. The percentage yield indicates the effectiveness of the preparation method and the extent of material loss during the manufacturing process. All measurements were performed in triplicate, and the average value was reported. [8]

Actual Weight of Product % Yield ----------------------------------------- ×100 Total Weight of Excipient and Drug Drug Entrapment Efficiency The drug entrapment efficiency of the prepared microspheres was determined by estimating the amount of drug encapsulated within the polymeric matrix. An accurately weighed quantity of microspheres equivalent to about 10 mg of drug was crushed and transferred into a suitable volumetric flask containing an appropriate solvent capable of dissolving both the drug and polymer. The mixture was sonicated for 15–30 minutes to ensure complete extraction of the entrapped drug and then filtered through a 0.45 μm membrane filter. The filtrate was suitably diluted and analyzed using a UV-Visible spectrophotometer at the predetermined wavelength (λmax) of the drug. The actual amount of drug present in the microspheres was calculated from the calibration curve. The drug entrapment efficiency was determined by comparing the experimentally measured drug content with the theoretical drug content of the formulation. [9]

% Drug Entrapment = Amount of Drug Actually Present / Theoretical Drug Loaded Expected × 100 Particle Size Analysis The particle size of the prepared microspheres was determined using a laser diffraction particle size analyzer. A known quantity of microspheres was dispersed in distilled water containing a small amount of surfactant (0.1% Tween 80) to prevent particle aggregation. The dispersion was sonicated for a few minutes to obtain a uniform suspension. The sample was then introduced into the particle size analyzer, and the mean particle size along with the particle size distribution was recorded. [10]

Morphological Characterization Using SEM The surface morphology and shape of the microspheres were examined using scanning electron microscopy (SEM). A small amount of dried microspheres was mounted on an aluminum stub using double-sided adhesive tape and coated with a thin layer of gold under vacuum using a sputter coater to enhance conductivity. The coated samples were observed under the SEM at suitable accelerating voltage and different magnifications. Photomicrographs were captured to evaluate the surface characteristics, shape, porosity, and structural integrity of the microspheres. [11]

In-Vitro Drug Release Study The in-vitro drug release study was carried out using USP dissolution apparatus II (paddle method). Microspheres equivalent to a predetermined quantity of drug were placed in 900 mL of dissolution medium maintained at 37 ± 0.5°C and stirred at 50 rpm. The dissolution medium generally consisted of 7.4 phosphate buffer. At specified time intervals, 5 mL samples were withdrawn and replaced with an equal volume of fresh dissolution medium maintained at the same temperature. The samples were filtered through a membrane filter and analyzed spectrophotometrically at the drug's λmax. The cumulative percentage drug release was calculated and plotted against time. [12]

Kinetics of Drug Release Studies To understand the mechanism of drug release from the microspheres, the dissolution data obtained from the in-vitro release studies were fitted into various kinetic models including Zero-order, First-order, Higuchi, Korsmeyer-Peppas, and Hixson-Crowell models. The cumulative percentage drug release data were plotted according to the mathematical equations of each model, and the correlation coefficient (R²) values were determined. The model exhibiting the highest R² value was considered the best-fit model and was used to explain the release mechanism, whether diffusion-controlled, erosion-controlled, or a combination of both. [13]

Stability Studies The stability studies of the optimized microsphere formulation were conducted according to ICH Q1A(R2) guidelines. The formulation was packed in suitable airtight containers and stored under accelerated stability conditions at 40 ± 2°C and 75 ± 5% relative humidity for a period of three months. Samples were withdrawn at predetermined intervals of 0, 1, 2, and 3 months and evaluated for physical appearance, particle size, drug content, entrapment efficiency, and in-vitro drug release characteristics. The results obtained after storage were compared with the initial values to assess any significant changes. The absence of noticeable variations in the evaluated parameters indicated good stability of the microsphere formulation during the storage period. [14]

Results and Discussion

Characterization of Microspheres Particle Size Analysis Fig 1: Particle size analysis of Optimized formulation Table 2: Particle size of Different formulations of Microspheres Formulation code Mean particle size* (µm) F1 293 F2 348 F3 367 F4 358 F5 268 F6 290 F7 253 F8 318

Discussion

Among all formulations, F7 exhibited the smallest particle size (253 µm), indicating efficient emulsification and solvent evaporation during preparation. Smaller particle size generally provides a larger surface area which facilitates uniform drug release and enhanced entrapment. The variation in particle size among formulations may be attributed to differences in polymer concentration and viscosity of the dispersed phase.

Discussion

The highest yield was observed for F7 (87.10%), indicating minimal material loss during preparation and effective microsphere formation. Increased polymer concentration may have improved the solidification process and reduced drug diffusion into the external phase, resulting in higher production yield.

Scanning Electronic Microscopy Fig 2: SEM Analysis of Optimized formulation

Discussion

No visible cracks or surface imperfections were observed. The spherical morphology confirms successful formation of microspheres by the solvent evaporation technique and contributes to sustained drug release behavior.

Drug Entrapment Efficiency Table 4: Drug entrapment for different formulation Formulation Drug Entrapment Efficiency F1 71.29 F2 82.25 F3 78.63 F4 77.81 F5 83.56 F6 85.90 F7 89.53 F8 80.25 Fig 3: Drug entrapment efficiency for different formulation

Discussion

The optimized formulation F7 showed the highest entrapment efficiency (89.53%). This may be attributed to the optimum polymer-to-drug ratio, which reduced drug diffusion during preparation and enhanced encapsulation. Higher entrapment efficiency is advantageous because it ensures uniform drug loading and minimizes drug wastage.

In-Vitro Drug Release Study Table 5: Comparative In-Vitro Drug Release Profile for Formulation in 7.4 phosphate buffer Time (hrs.) F1 F2 F3 F4 F5 F6 F7 F8 0 0 0 0 0 0 0 0 0 Fig 4: Comparative In-Vitro Drug Release Profile Of ( F1-F4) formulation Fig 5: Comparative In-Vitro Drug Release Profile Of ( F5-F8) formulation

Discussion

The optimized formulation f7 exhibited the highest drug release (99.43%) at 12 hours. Initially, a moderate release was observed due to the release of surface-associated drug, followed by a controlled release phase resulting from diffusion through the polymer matrix. The sustained release profile suggests that the microspheres are capable of maintaining prolonged drug availability and reducing dosing frequency.

Drug Release Kinetics Zero Order Kinetics Fig 6: Zero order kinetics of optimized formulation First Order Kinetics Fig 7: First order kinetics optimized formulation Higuchi Model Fig 8: Higuchi model optimized formulation Korsmeyer Peppas Fig 9: Korsmeyer peppas optimized formulation

Discussion

Based on the overall kinetic analysis, the optimized formulation F7 predominantly followed the Higuchi diffusion model with contribution from anomalous diffusion mechanisms.

Stability Study Stability study was carried out for the F7 formulation by exposing it to different temperature 25°C, 30°C and 40°C for 90 days. The sample was analyzed for drug content at the regular intervals. It was found that no remarkable change in the drug release of F7 formulation. This indicates that F7 was stable for following temperature.

Table 6: Results of stability studies of optimized formulation F-7 S.NO Time in days Physical changes Mean % drug release Lacosamide 250C/60% 300C/75% 400C/75%

Conclusion

Lacosamide-loaded microspheres were successfully formulated and evaluated for sustained drug delivery. FTIR studies confirmed compatibility between Lacosamide and the selected excipients, while SEM analysis demonstrated the formation of spherical and uniform microspheres. Among all formulations, F7 was identified as the optimized formulation based on its smallest particle size (253 µm), highest percentage yield (87.10%), highest drug entrapment efficiency (89.53%), and maximum cumulative drug release (99.43% at 12 hours). The optimized microspheres provided a controlled and sustained release of Lacosamide over 12 hours, which may help in maintaining therapeutic drug levels for an extended period and reducing dosing frequency. Drug release kinetics suggested a diffusion-controlled mechanism, and stability studies confirmed that the formulation remained stable under various storage conditions for 90 days. Therefore, the developed Lacosamide microsphere formulation (F7) can be considered a promising sustained-release drug delivery system for improving the therapeutic effectiveness and patient compliance in the management of epilepsy. Further in-vivo studies are recommended to establish its clinical potential.