Preparation and evaluation of cilnidipine microemulsion.

Cilnidipine, a calcium channel blocker having neuroprotective action and BCS Class II drug, hence formulating in Microemulsion will increase solubility, absorption and bioavailability. The formulation was prepared using titration method by tocotrienol, tween 20 and transcutol HP as oil, surfactant and co-surfactant and characterized for dilutability, dye solubility, assay (98.39±0.06), pH (6.6±1.5), Viscosity (98±1.0 cps) and Conductivity (0.2±0.09 μS/cm). The formulation was optimized on basis of percentage transmittance (99.269±0.23 at 700 nm), Globule size (13.31±4.3 nm) and zeta potential (-11.4±2.3 mV). Cilnidipine microemulsion was found to be stable for 3 months.

Microemulsion is defined as a dispersion consisting of oil, surfactant, cosurfactant and aqueous phase, which is a single optically isotropic and thermodynamically stable liquid solution with a droplet diameter usually within the range of 10–100 nm. Microemulsions are used as potential drug delivery vehicles, largely due to simple manufacturing, scale up feasibility and do not require specialized equipments. Oil-in-water (o/w) microemulsion is the most suitable formulation, which is expected to increase the solubility by dissolving compounds with low water solubility into an oil phase. Thus Cilnidipine is an ideal candidate for microemulsion to enhance its oral bioavailability by reducing the droplet size, and hence increase the rate of absorption due to surfactant-induced permeability changes.

Materials and Methods

Materials

Tocotrienol rich fraction (TRF) oil, Cilnidipine, Capmul MCM C8, Capmul MCM, Capmul MCM L8, Captex, Labrasol, Labrafac Lipofile, Transcutol HP, Lauroglycol FCC, Tween-20, Tween-80, Polyethylene glycol (PEG)-200 and 400, Methanol, Isopropyl Myristate, Oleic acid.

Methods

Selection of oil, surfactant and co surfactant was done on the basis of solubility of drug. The formulation was prepared using titration method by phase diagram and optimized on basis of percentage transmittance, particle size and zeta potential.

Preparation of drug loaded microemulsion

Microemulsion was prepared using constant ratio of surfactant (S)/co surfactant (CoS), various combinations of oil and S/CoS were produced. The water was added drop wise. After the addition of each drop, the mixture was stirred and observed. In microemulsion system the distilled water was used as an external phase.

Characterization of microemulsion

Prepared Microemulsion was characterized for Clarity, Dilutability, Assay, Globule size determination, Zeta-potential, pH, Viscosity, Dye solubility and Conductivity. Stirring speed and Time of Rotation were optimized as process parameters.

Results and Discussion

Solubility study

Solubility results are shown in Table 1.

Table 1

Results of solubility studies

Preliminary phase diagram of oil, surfactant and water systems

Selection and optimization of formulation parameters

Microemulsions are essentially clear systems and hence solubility of drug in all the components is necessary. From different components used and data available, highest solubility of Cilnidipine was found in Tocotrienol, Tween 20 and transcutol HP, and hence Tween 20 and transcutol HP had been selected as surfactant and cosurfactant respectively. Selection of oil and surfactant, and the mixing ratio of oil to S/CoS can be ascertained by pseudoternary phase diagram as it differentiates the microemulsion region from that of macroemulsion region. Microemulsion region from pseudoternary phase diagram was selected for TRF: Tween 20: Transcutol HP system highest region was found in 3:1 ratio and hence this ratio was selected for further preparation.

Optimization of process parameters

The stirring speed and the time of rotation were optimized at low speed (150-200 RPM) and 10 minutes respectively (Size: 16.3±4.5 nm.).

Characterization

The characteristics of the optimized microemulsion formulations are depicted in following Table 2

Table 2

Characterization of microemulsion

Particle size distribution

Stability study

Prepared microemulsion was found to be stable for three months at ambient temperature as no phase separation or flocculation was observed during storage period. The Microemulsion was subjected to globule size and zeta potential measurements after three months of storage and the results were found to be satisfactory and hence the Microemulsion was found to be stable during this period.

Conclusion

Cilnidipine microemulsion was prepared successfully by water titration method. The prepared formulations exhibit all the desirable attributes of an ideal microemulsion and were also found to be stable for 3 months. From study, it was concluded that microemulsion prepared using tocotrienol as oil will be useful to improve solubility and bioavailability of cilnidipine.