EMULSI
DR. apt. Audia Triani Olii S.Farm., M.Si.
Definition
• An emulsion is a heterogeneous preparation composed of two
immiscible liquids (by convention described as oil and water), one of
which is dispersed as fine droplets uniformly throughout the other
• Emulsions are thermodynamically unstable and revert back to
separate oil and water phases by fusion or coalescence of droplets
unless kinetically stabilized by a third component, the emulsifying
agent
• The phase present as small droplets is called the
disperse, dispersed, or internal phase and the
supporting liquid is known as the continuous or
external phase
• Droplet diameters vary enormously, but in
pharmaceutical emulsions they are typically
polydispersed with diameters ranging from
approximately 0.1 to 50 mm.
• Emulsions are conveniently classified as oil-in-
water (o/w) or waterin-oil (w/o), depending on
whether the continuous phase is aqueous or
oily
• Multiple emulsions, which are prepared from oil and water by the
reemulsification of an existing emulsion so as to provide two dispersed
phases, are also of pharmaceutical interest. Multiple emulsions of the oil-in-
water-in-oil (o/w/o) type are w/o emulsions in which the water globules
themselves contain dispersed oil globules; conversely, water-in-oil-in-water
(w/o/w) emulsions are those where the internal and external aqueous
phases are separated by the oil
Pharmaceutical applications
1. Traditionally the term ‘‘emulsion’’ is restricted to mobile emulsions
for internal use; emulsions for external use are described by their
pharmaceutical types as liniments, lotions, and creamsTo over come
the instability of certain drug in aqueous solution:
2. Both oil-in-water and water-in-oil emulsions are extensively used for
their therapeutic properties and/or as vehicles to deliver drugs and
cosmetic agents to the skin. The emulsion facilitates drug
permeation into and through the skin by its occlusive effects and/or
by the incorporation of penetration-enhancing componentsReduce
the contact time between solid drug particles and dispersion media
increase the stability of drug like Ampicillin by making it as
reconstituted powder.
3. Oral emulsions are almost exclusively of the oil-inwater type. They
provide a degree of taste masking as the aqueous external phase
effectively isolates the oil from the tongue
4. The type of emulsion used parenterally depends on the route of
injection and the intended use.[13–15] Oil-inwater emulsions are
administered by all the major parenteral routes whereas water-in-oil
emulsions are generally reserved for intramuscular or subcutaneous
administration where sustained release is required
5. Sterile parenteral oil-in-water emulsions have been used extensively
for over 40 years for the intravenous administration of fats,
carbohydrates, and vitamins to debilitated patients. Several vegetable
oil-in-water emulsions are now available commercially with droplet
sizes similar to that of chylomicrons (approximately 0.5–2 mm),
vitamin K, vitamin A
6. Radiopaque emulsions, which have long been used as contrast
media in conventional X-ray examinations of body organs, are
finding further application with more sophisticated techniques
including computed tomography, ultrasound, and nuclear magnetic
resonance. The first commercial product, Fluosol-DA (Green Cross
Corporation, Osaka, Japan)
7. There are only a few studies on the ocular and nasal applications of
emulsions
Adventages of emulsion
1. Unpalatable oils can be administered in a palatable form.
2. The aqueous phase is easily flavored
3. The taste of oils can be masked.
4. Absorption is faster when compared to solid dosage forms
5. It is possible to include two incompatible ingredients, one in each
phase of the emulsion.
6. Semisolid emulsions are O/W (vanishing creams) or W/O (cold
creams). O/W emulsions are preferred over W/O emulsions. They
can be easily rubbed into the skin and can be easily removed by
washing
Disadventages
1. Calculation of primary emulsion formulae and technical expertise are
needed for the manufacture of stable emulsions.
2. A measuring device is needed for administration.
3. Emulsions require shaking before use to ensure uniformity of dose.
4. If the preparation is not shaken well, the accuracy of the dose is likely to
be less when compared to solutions.
5. Improper storage conditions can affect the disperse system.
6. Since emulsions are stored in glass or plastic containers, they are bulky,
difficult to transport, and prone to container breakages.
7. Microbial contamination of emulsions can lead to cracking.
•
Emulsion Stability
• A stable emulsion is considered to be one in which the dispersed
droplets retain their initial character and remain uniformly distributed
throughout the continuous phase for the desired shelf life
• There should be no phase changes or microbial contamination on
storage, and the emulsion should maintain elegance with respect to
odor, color, and consistency.
• . Instabilities of both chemical and physical origins can occur in
emulsion formulations
1. Physical Instability
a. Flocculation describes a weak reversible association between emulsion globules
separated by thin films of continuous phase. Flocculation is generally regarded as
a precursor to the irreversible process of coalescence
b. Coalescence, where dispersed phase droplets merge to form larger droplets,
takes place in two distinct stages. It begins with the drainage of liquid films of
continuous phase from between the oil droplets as they approach one another
and ends with the rupture of the film when a critical thickness is reached
c. Otswald ripening, where droplet sizes increase due to
large droplets growing at the expense of smaller ones,
may also occur. This destabilizing process is a result of the
Kelvin effect and occurs when small emulsion droplets
(less than 1 mm) have higher solubilities (and vapor
pressures) than do larger droplets (i.e., the bulk material)
and consequently are thermodynamically unstable
d. Phase inversion when an oil-in-water emulsion inverts to form a
water-in-oil emulsion or visa versa is a special case of irreversible
instability that occurs only under welldefined conditions such as a
change in emulsifier solubility due to specific interactions with
additives or to a change in temperature
e. Creaming or sedimentation occurs when the dispersed droplets or
floccules separate under the influence of gravity to form a layer of
more concentrated emulsion, the cream. Generally a creamed
emulsion can be restored to its original state by gentle agitation.
Most oils are less dense than water so that the oil droplets in o/w
emulsions rise to the surface to form an upper layer of cream
Emulgator
What is???
• Emulgator surface-active agents that act at the interface between
the two immiscible liquids. Their main roles are to promote
emulsion formation and to stabilize the emulsion
• Emulgator contain an oil-soluble, lipophilic tail that reacts with the
oil and a water-soluble, hydrophilic head that reacts with the water
at the interface of the dispersed droplet
Mechanisms of Emulsion Stabilization
1. Electrostatic Repulsion
Electrostatic force results from the interaction
between the electrical double layers around
the charged droplets which tend to prevent
droplet contact. This mechanism occurs by
adsorption of an ionic surfactant
The emulsion stability is not due to the electrostatic forces, but it is
becauseof the strength of the interfacial film surrounding the
dispersed droplets
2. Steric Repulsion
Steric stabilization is generally found in the systems stabilized by
non-ionic surfactants and polymers. In this mechanism, the
dispersed water droplets will be covered by surfactant molecules
and the surfactant tail adsorbed on the surface of the particles
prevents droplets to have a close contact
3. Marangoni –Gibbs Effect
The Marangoni-Gibbs effect can stabilize emulsions by preventing the
drainage of the continuous phase from between two opposing droplets.
This effect occurs due to the deformation of the droplet surface area as
they get close along together. When the droplets approach together
they make a parallel surface and the film layer attempts to drain
4. Thin Film Stabilization
In this step, the formation of a rigid and viscoelastic film surrounds
the water droplets and prevents the droplets from coalescence.
This process can be quite complex and depends on asphaltene
chemistry, solvency and the kinetics of diffusion and adsorption
Type of emulsifier
1. Natural emulsifier : Gom arab, tragacanth, metyl cellulosa,
CMC, magnesium, aluminium silikat, veegum,bentonit.
2. Synthetic emulsifier
a. Anionic : Na lauryl sulfat
b. Krtionic : ammonium qartener
c. Non ionic : Span, Tween
d. Amphoteric : protein, lecitin
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