Microemulsions are transparent or translucent systems consisting of oil, water, and surfactant, usually along with a co-surfactant. They have droplet sizes between 20-200 nm and are isotropic and thermodynamically stable. Microemulsions can solubilize both hydrophilic and lipophilic drugs, resulting in increased absorption and bioavailability compared to emulsions. While microemulsions provide benefits like increased drug solubility and absorption, their use is limited by potential toxicity of large surfactant concentrations and instability based on environmental factors.

2. Contents:
 Definition
 Components
 An oily phase
 An aqueous phase
 Surfactant
 Co-surfactant
 Difference b/w emulsion and
microemulsion
 Preparation of microemulsion
 Advantages
 Disadvantages

3. Microemulsions are isotropic, thermodynamically stable
transparent (or translucent) systems of oil, water and
surfactant, frequently in combination with a cosurfactant
with a droplet size usually in the range of 20-200 nm.

5.  The most important excipient in formulation is oil phase,
because it can solubilize the required dose of the
lipophilic drug.
 It also increases the fraction of lipophilic drug
transported via the intestinal lymphatic system thereby
increasing absorption from GIT.
 Choice of Oil phase selection depends upon solubility of
drug.
 Example:
Mineral oil

6.  It contains hydrophilic active ingredients and
preservatives.
 Buffer solutions are also used as aqueous phase.pH of
the aqueous phase should be maintained between 7-8.

7.  Surfactants are wetting agents that lowers the interfacial
tension between 2 immiscible liquids.
 Examples:
Span, Tween

8. Allows the interfacial film a sufficient flexibility which can
readily deform around the droplets
Increase the fluidity of the interface and reduces
viscosity of formulation thereby increasing the
bioavailability of drug
Short to medium chain length alcohols are commonly
added as co-surfactants.
Example: Ethylene glycol, Propylene glycol

9. Properties Emulsion Microemulsion
Appearance Cloudy Transparent
Interfacial tension High Ultra Low
Droplet size ˃500nm 20-200nm
Phases Biphasic Mono phasic
Viscosity Higher viscosity
Lower viscosity with
Newtonian behavior
Stability
Thermodynamically
unstable
Thermodynamically
stable

10. Properties Emulsion Microemulsion
Phases Monophasic Biphasic
Preparation
Facile preparation,
relatively lower cost for
commercial production
Require a large input of
energy, higher cost
Viscosity
Low viscosity with
Newtonian behavior
Higher viscosity

12.  The drug is dissolved in the Lipophilic part of microemulsion i.e. oil phase.
 Water phase is combined with surfactant and a co-surfactant is then added at
slow rate with gradual stirring until the system is transparent.
 Amount of surfactant and co-surfactant to be added and the percent of oil
phase that can be incorporated shall be determined with the help of pseudo-
ternary phase diagram.
 Ultrasonicator can finally be used to achieve the desired size range for
dispersed globules.
 It is then be allowed to equilibrate.

13.  Microemulsion acts as supersolvent for the drugs and it has the ability to
solubilize both hydrophilic and lipophilic drugs.
 Increased rate of absorption and Increased bioavailability of drug, due to
very small droplet size.
 Increased patient compliance due to liquid dosage form.
 Helpful in taste masking
 Rapid and efficient penetration of drug moiety.
 Easy manufacturing because it requires minimum energy for formation.

14.  Use of large concentration of surfactants and co-surfactants may leads
to toxicity problems.
 Microemulsions have limited solubilizing capacity for high-melting
substances.
 Microemulsion stability is influenced by environmental parameters such
as temperature and pH, which may cause phase separation