Like simple emulsion multiple emulsion are classified into two type.
The immiscible phase ,which separates the two miscible phase is known as “liquid membrane” and act as a diffusion barrier and semipermeable membrane for drugs or moities entrapped in the internal aqueous phase.
In this method a W/O emulsion(dispersed phase) is extruded into a an external aqueous phase(continuous phase) with a constant pressure through a porous glass membrane which should have controlled and homogenous pores.
The relationship between membrane pore size and droplet size of W/O/W emulsion is given by following equation :
Use of large concentration of surfactant and cosurfactant necessary for solubilizing the nanodroplets.
Limited solubilizing capacity for high melting substances.
The surfactant must be non toxic for using pharmaceutical application.
Microemulsion stability is influenced by environmental parameters such as temperature and pH. These parameters change upon microemulsion delivery to patients.
09/26/11 Shakti Suthar
Difference between Ordinary emulsion and Microemulsion: 09/26/11 Shakti Suthar Ordinary emulsion Microemulsion Size of globule: 0.5-50 µm 0.1-10 µm Appearance: Turbid Clear Thermodynamically: Stable but coalesce finally. More stable Viscosity: - Less compared to other emulsion. Preparation: It require high shear condition By simple mixing of the component and do not require high shear condition Surfactant concentration: 2-3 %Waight 6-8 %Waight Phases: 2 1
Transparency of microemulsion formulation was determined by measuring percentage transmittance through U.V. Spectrophotometer.
2)Droplet Size Analysis:
By microscopic method
6)Stability Studies: The optimized ME was stored at
three different temperature ranges for 6 months i.e.,
refrigerating condition (2 0 C – 8 0 C), room temperature and elevated temperature (50 ± 2 0 C) and shelf life of the stored microemulsion system was evaluated by visual inspection (phase separation), % transmittance, Particle size and % Assay.
Self-emulsifying drug delivery systems (SEDDS) are usually used to improve the bioavailability of hydrophobic drugs.
Approximately 40% of new chemical entities exhibit poor aqueous solubility and present a major challenge to modern drug delivery system, because of their low bioavailability.
SEDDS is ideally an isotropic mixture of oils and surfactants and sometimes co solvents.
The multi-component delivery systems have optimized by evaluating their ability to self-emulsify when introduced to an aqueous medium under gentle agitation, and by determination of particle size of the resulting emulsion .
Upon oral administration,these systems form fine (micro) emulsions in the gastrointestinal tract (GIT) with mild agitation provided by gastric mobility.
Fine oil droplets would pass rapidly from the stomach and promote wide distribution of the drug throughout the GI tract, thereby minimizing the irritation frequently encountered during extended contact between bulk drug substances and the gut wall.
When compared with emulsions, which are sensitive and metastable dispersed forms, SEDDS are physically stable formulations that are easy to manufacture.
Oils can solubilize the lipophilic drug in a specific amount.
It is the most important excipient because it can facilitate self-emulsification and increase the fraction of lipophilic drug transported via the intestinal lymphatic system, thereby increasing absorption from the GI tract.
Mainly triglycerides are use.
Nonionic surfactants with high hydrophilic–lipophilic balance (HLB) values are used in formulation of SEDDSs.
Visual assessment . This may provide important information about the self-emulsifying and microemulsifying property of the mixture and about the resulting dispersion.
Turbidity Measurement . This is to identify efficient self-emulsification by establishing whether the dispersion reaches equilibrium rapidly and in a reproducible time.
Droplet Size . This is a crucial factor in self-emulsification performance because it determines the rate and extent of drug release as well as the stability of the emulsion. Photon correlation spectroscopy, microscopic techniques or a Coulter Nanosizer are mainly used for the determination of the emulsion droplet size. The reduction of the droplet size to values below 50 μm leads to the formation of SMEDDSs, which are stable and clear o/w dispersions.
Chemical instabilities of drugs and high surfactant concentrations. The large quantity of surfactant in self-emulsifying formulations (30-60%) irritates GIT. Consequently, the safety aspect of the surfactant vehicle had to be considered.
Volatile cosolvents in the conventional self-emulsifying formulations are known to migrate into the shells of soft or hard gelatin capsules, resulting in the precipitation of the lipophilic drugs.