Pharmaceutics Final Exam Review: Emulsions- heterogeneous systemsof one liquid dispersed in another in the form of droplets usually exceeding 0.1 micrometers in diameter. Dispersed phase- internal phase Dispersion medium- external phase/continuous phase different types- o/w, w/oDilution method: If the emulsion mixes freely with water, it is a o/w type. Conductivity method: If the external phase is water, current will pass through the emulsion. if an oil is the continuous phase the emulsion will not conduct electricity. Dye solubility test: A water soluble dye will be uniformly distributed in the external phase if it is o/w type. Medicinal emulsions for oral administration are usually of the o/w type. Requires use of o/w emulsifying agent: nonionic surfactants, acacia, tragacanth, gelatin. o/w type can also be prepared with monovalent soaps such as sodium oleate, sodium lauryl sulfate. Externally applied emulsions are usually w/o type. w/o type emulsions are prepared with polyvalent soaps such as calcium palmitate, sorbitan esters (Spans), cholesterol and wool fat. Micro and multiple emulsions- differencefromnormal emulsionsMicroemulsions- Microemulsions have nanometer sized droplets of an immiscible liquid dispersed in another liquid. The components are water, oil, a surfactant and a cosurfactant (short chain alcohol). a particle size is in the range of 100-200nm Preparation:Dilution of oil-surfactant mixture with water(o/w ) Dilution of water-surfactant with oil (w/o) High concentration of surfactant is required (6-8%) Spontaneous emulsification (self-emulsifying) Microemulsions differ from conventional emulsions:Form spontaneously without aid of mechanical means Optical transparency and low viscosity Appears as if they are true solutions, shows Newtonian flow More stable, have longer shelf-life. Greater bioavailability of drugs contained in the ME Examples: Estrasorb: estradiol emulsified in soyabean oil, polysorbate and ethanol AND Topicaine: Lidocaine emulsified in Jojoba oil with glyceryl monostearate and benzyl alcohol Multiple emulsions (double emulsions)- Water in oil and oil in water exists simultaneously, stabilized by respective surface active agents (hydrophilic and lipophilic surfactants). w/o/w, o/w/o Emulsifying an emulsionin to a second external phase. “emulsions of emulsions”. Example:
A w/o emulsion is prepared first from liquid petrolatum and water with sorbitan monooleate. This emulsion (w/o) is emulsified further with an aqueous solution of tween 80 to form the final w/o/w/ Applications of multiple emulsions-Protects API from degradation. Vitamin C and E from oxidative degradation.