BIPHASIC LIQUID DOSAGE FORM

1. Pharmaceutical
Emulsions

2. Outlines
•Introduction
•Theoretical Aspects
•Types and Applications
•Emulsion Stability
•Formulation of Emulsion
•Properties of Emulsion and Emulsifiers

3. Introduction
• It consists of a two-phase system prepared by
combining two immiscible liquids, one of which is
dispersed uniformly throughout the other.
• Internal phase = the dispersed phase,
• External phase or dispersion medium = continuous phase.

4. • The liquid that is dispersed into small droplets is called
the dispersedphase
or internal phase
or discontinuous phase
• The other liquid is the dispersion medium
continuous phase
external phase

5. A. Two immiscible liquids,
not emulsified.
B. An emulsion of Phase
B dispersed in Phase
A.
C. The unstable emulsion
regressively separates.
D. The surfactant positions
itself on the interfaces
between Phase A and
Phase B, stabilizing the
emulsion.

6. Emulsions are unstable because:
the globules of the dispersed liquid tend to coalesce
to form large globules until all of the dispersed
globules have coalesced.
• An emulsifying agent is usually added to the system to
prevent the coalescence of the globules and maintain
the integrity of the individual globules of the dispersed
phase.

7. •Emulsions tend to have a cloudy appearance,
because the many phase interfaces (the boundary
between the phases is called the interface) scatter
light that passes through the emulsion. Emulsions
are unstable and thus do not form spontaneously.
Energy input through shaking, stirring,
homogenizers, or spray processes are needed to
form an emulsion.
•Over time, emulsions tend to revert to the stable
state of oil separated from water. Surface active
substances (surfactants) can increase the kinetic
stability of emulsions greatly so that, once formed,
the emulsion does not change significantly over
years of storage.

8. •A phenomenon is called coalescence, and
happens when small droplets recombine to form
bigger ones. Fluid emulsions can also suffer from
creaming, the migration of one of the substances
to the top of the emulsion.
•Emulsions are part of a more general class of two-
phase systems of matter called colloids. Although
the terms colloid and emulsion are sometimes
used interchangeably, emulsion tends to imply
that both the dispersed and the continuous phase
are liquid.

9. • There are three types of emulsion instability:
1. Flocculation, where the particles form clumps;
2. Creaming, where the particles concentrate
towards the surface of the mixture while staying
separated; and
3. Breaking, where the particles coalesce and form a
layer of liquid.

10. Emulsifier:
• An emulsifier (or surfactant) is a substance which
stabilizes an emulsion.
• Detergents are another class of surfactant, and
will chemically interact with both oil and water,
thus stabilizing the interface between oil or water
droplets in suspension.
• This principle is exploited in soap to remove
grease for the purpose of cleaning.
• A wide variety of emulsifiers are used in pharmacy
to prepare emulsions such as creams and lotions.

11. 20 ml ampule of 1% propofol emulsion suitable for
intravenous injection.

12. • When oil is the dispersed phase and an aqueous
solution is the continuous phase, the system is
designated as an oil-in-water (O/W) emulsion.
• Conversely, where water or an aqueous solution is
the dispersed phase and oil or oleaginous material
is the continuous phase, the system is designated
as water-in-oil (W/O) emulsion.

13. • Oil-in-water (O/W) emulsion used for oral
and intravenous administration .
• Water-in-oil (W/O) emulsion used for
intramuscular injections for a depot effect
(extended release or long acting effect).

14. • Oil-in-water (O/W) emulsion :
• Water-in-oil (W/O) emulsion :

15. • Multiple Emulsion Method: multiphase emulsions are
prepared by the solvent evaporation technique by a
three-step emulsification process.
• Aqueous drug solution and oil phase containing
emulsion stabilizers are combined to give a water-in-oil
emulsion (step 1). Later the w/o emulsion is dispersed
in the polymer solution (step 2). The solvent is
evaporated under reduced pressure.
• In other way: preparation of a primary o/w emulsion in
which the ‘oily dispersed phase’ in an organic solution
of the drug and the ‘aqueous continuous phase’ is an
aqueous solution containing chitosan and an
emulsifier (step 1); multiple emulsion formation with a
‘oily outer phase’ (step 2); and finally, cross-linkage
adding a cross-linking agent.

16. Hint:
Hydrophobic drugs are prepared
using o/w/o multiple emulsion
method.
Hydrophilic drugs are prepared
using w/o/w multiple emulsion
method.

17. Why would you want an o/w emulsion instead
of a w/o emulsion for an oral dosage form?
• The continuous water phase would be more palatable to
the mouth and the liquid consistency would be easier to
flow through the mouth and down the throat.
• By dispersing a foul tasting or smelling drug in the oil
phase, your taste buds and your sense of smell will be
unaware of the agent passing by.
• In addition, in the o/w emulsion the manufacturer can
add sweeteners and flavors to the continuous phase
which will be experienced by the taste buds as the
medication passes over them.

18. Advantages of emulsions over other liquid
forms:
1- The unpleasant taste or odor of an oil can be
masked partially or wholly, by emulsification
2- The solubility of many drugs is increased when
they are incorporated into emulsions
3- The stability of many drugs which are unstable in
aqueous solutions is increased when incorporated
into an emulsion

19. 4- Prolonged drug action and increased
bioavailability are often obtained when drugs are
incorporated into emulsions
5- The appearance of oleaginous materials intended
for topical applications is usually improved when
formulated in an emulsified form

20. Emulsion Stability
• Flocculation and Coalescence:
if no protective barrier is present at the
interface, or if very low surface coverage
by emulsifier exists, emulsion droplets
rapidly aggregate and coalesce. Even
though coverage sufficient to prevent
coalescence may exist, however, a
relatively weak particle-particle
interaction known as flocculation may
occur. Flocculation is differentiated from
coalescence primarily by the fact that the
interfacial film remains intact and that
aggregation may be reserved.

21. Emulsion Stability
• Flocculation and Coalescence (…cont.):
While flocculation (aggregation) is the
clumping together of particles, coalescence is
the fusing of the agglomerates into a large
drop, or drops.
Coalescence is usually rapid when two
Immiscible liquids are shaken together, since
there is no large energy barrier to prevent
fusion of drops or reformation of the original
bulk phases.

22. Emulsion Stability
• Flocculation and Coalescence (…cont.):
When an emulsifying agent is added to
the system, flocculation still may occur
but coalescence is reduced to an extent
depending on the efficacy of the
emulsifying agent to form a stable,
coherent interfacial film. It is therefore
possible to prepare emulsions that are
flocculated, yet which do not coalesce.

23. Emulsion Stability
• An emulsion is considered unstable if:
a. The internal phase tends to form globule
aggregates
b. Large globules rise to the top (cream) or fall
to the bottom to form a concentrated layer
of emulsified internal phase globules
c. If the emulsion breaks (coalescence of the
internal phase globules into a distinct
phase). In other words, the separation of the
internal phase from the emulsion, and the
emulsion is described being cracked or
broken.

24. Emulsion Stability
• What causes an emulsion to break?
The globules coalesce due to too little emulsifying agent in
the first place or possibly due to degradation of the
emulsifying
agents by chemical or enzymatic (from microbes or other
sources) means. Sterility isn't necessary with oral emulsions,
but destruction of the microbes can improve the physical
stability of emulsion formulations.
Fungistatic preservatives are generally included because fungi
(molds and yeasts) are more likely to contaminate emulsions
than are bacteria.

25. Emulsion Stability
• What causes an emulsion to break?
Methylparaben and propylparaben are frequently used to serve
this function. Alcohol at 12-15%, based on the aqueous
volume, is frequently added to oral o/w emulsions for
preservation.
Care must be taken to protect emulsions against extremes of
cold and heat. Freezing and thawing causes a coarsening
of an emulsion and sometimes causes breaking. Excessive
heat has the same effect.
Light-resistant containers which can seal tightly should be
used to protect the emulsion from photolysis and
oxidation. Chemical antioxidants are usually employed.

26. Emulsion Stability
• In light of these considerations, the instability of
pharmaceutical emulsions may be classified as
follows:
• Flocculation and creaming
• Coalescence and breaking
• Miscellaneous physical and chemical changes
• Phase inversion

27. Emulsion Stability
• Creaming and Stokes’ Law:
• Those factors that find importance in the
creaming of an emulsion are related by Stokes’
Law. The limitations of this equation to actual
systems have been discussed previously for
pharmaceutical suspensions, and these apply
equally to emulsified systems.

28. Emulsion Stability
• Creaming and Stokes’ Law (…cont.)
• Analysis of the equation shows that if the dispersed
phase is less dense than the continuous phase, which is
generally the case in the o/w emulsions, the velocity of
sedimentation becomes negative, that is, an upward
creaming results. If the internal phase is heavier than
the external phase, the globules settle, a phenomenon
customarily noted in w/o emulsions in which the
internal aqueous phase is more dense than the
continuous oil phase. This effect may be referred to as
creaming in a downward direction. The diameter of
globules is seen to be a major factor in determining the
rate of creaming.

29. Formulation of Emulsion
• It is difficult to designate a general approach
and set of rules for selecting the materials, and
their amounts, required to formulate a desired
product.
• Although there are obvious situations in which
certain oils, emulsifiers, and other ingredients
must be avoided or used exclusively, decisions
of such a specific nature are made ultimately
on the basis of the experience and personal
tastes of the emulsion formulator, and
considerable trial and error.

30. Properties of emulsions
• A). Oil Phase and Water Phase: the materials
making up the oil portion of an emulsion and their
relative amounts are determined primarily by the
ultimate use of the product, the optional toxicity of
the oil, consistency desired, and the possible
chemical incompatibilities with other ingredients.
• For pharmaceutical and cosmetics products, the oil
phase is restricted to various grades of mineral oil; a
number of edible vegetable oils, such as those
derived from corn, peanuts, sesame, and olives; and
semi-solid and solid substances such as petroleum,
lanolin, beeswax, and long chain acids and alcohols.

31. Properties of emulsions
• A). Oil Phase and Water Phase:
• Isopropyl and myristate, a clear viscous liquid, is also a
popular ingredient used in dermatological and cosmetic
formulations.
• Chemical decomposition of vegetable oils and mineral
oil by means of oxidation is common problem that has
to be considered, particularly for those systems that
must be subjected to heat.

32. Properties of emulsions
• B). Phase Volume Ratio:
• For fluid emulsions it has been suggested that a 40
to 60 percent internal phase volume produces
acceptable emulsions with minimal difficulty.
• The use of lower percentages makes it difficult to
avoid creaming and sedimentation unless the
external phase viscosity is increased by the addition
of suitable substances, e.g. hydrophilic colloids.

33. Properties of emulsions
• C). Emulsifying agent:
• an emulsifier functions and operationally defined as a
stabilizer of the droplet form (globules) of the internal
phase.
• On the basis of their structure, emulsifiers (wetting agents or
surfactants) may be described as molecules comprising both
hydrophilic (oleophobic) and hydrophobic (oleophilic)
portions.
• For this reason, this group of compounds is frequently called
amphiphilic (i.e. water- and oil-loving).

34. Desired features of emulsifier
• It must be compatible with the other components in the
formulation, which means it must not interfere with the
chemical stability of each of the components or with the
therapeutic efficacy of the drug.
• It must be stable in the preparation itself. If it decomposes or
degrades, what good is it?
• The agent must be nontoxic.
• It should not possess an unacceptable odor, taste or color.
• It must assist in the formation of and continue to support the
emulsified system throughout the shelf-life of the product.
• 6. The cost of emulsifiers

35. Desired features of emulsifier
Emulsifying agents, in general, assist in the formation
of emulsion by three mechanisms:
• A. Reduction of interfacial tension (thermodynamic
stabilization).
• B. Formation of a rigid interfacial film (mechanical
barrier to coalescence).
• C. Formation of an electrical double layer (electrical
barrier to approach of particles).

36. Types of emulsifier
Carbohydrates: naturally occurring agents such as
acacia, tragacanth, agar, and pectin.
• These agents generally help to produce o/w
emulsions.
• Acacia is probably the most common emulsifier for
extemporaneous preparations. It is an acidic
polysaccharide.
• These agents are also called hydrophilic colloids.
They influence an emulsion by increasing the
viscosity of the aqueous phase.

37. Types of emulsifier
Macromolecules such as proteins:
• Naturally occurring agents such as gelatin, egg white
and casein, which also help to produce o/w
emulsions.
2.They are not very popular since they form thin
emulsions, but more importantly because they
decompose rapidly which results in a broken
emulsion.

38. Types of emulsifier
High molecular weight alcohols:
such as stearyl alcohol (18 carbons) and cetyl alcohol (16
carbons).
Finely divided solids:
such as bentonite, magnesium hydroxide or aluminum
hydroxide. They have shown to be good emulsifiers
alone and in combination with surfactants and/or
macromolecules.

39. Types of emulsifier
Important Note:
All these emulsifiers have in
common the ability to accumulate
at the oil-water interface,
as well as the tendency to influence
the degree of particle flocculation,
and hence the viscosity of
the emulsion.

40. Types of emulsifier
Important Note:
The major requirement of a potential emulsifying agent is that it
readily form a film a round each droplet of dispersed material.
The main purpose of this film, which can be a monolayer, a multilayer,
or a collection of small particles adsorbed around the interface, is to
form a barrier which prevents the coalescence of droplets that come
into contact with one another.
For the film to be an efficient barrier, it should possess some degree of
surface elasticity and should not thin out and rupture when sandwiched
between two droplets. If broken, the film should have the capacity to
reform rapidly.

41. Hydrophilic-Lipophilic Balance (HLB) System
• A convenient way to choosing emulsifiers involves the use of
a numerical scale for characterization.
• One such approach assigns to an emulsifier a hydrophile-lipophile
balance value (HLB), which is characteristic of its relative polarity.
• This approach is empirical and essentially no different from choosing a
series of any type of emulsifiers. The advantage of HLB system is that
to a first approximation one can compare any chemical type when both
polar and nonpolar groups are different. With regard to the specific
choice of an emulsifier,
• it has been suggested that surfactants having an HLB value of 3 to 6
should be used for obtaining w/o emulsions, whereas values of 8 to 18
are suitable for forming o/w emulsions.

42. Hydrophilic-Lipophilic Balance (HLB) System
• Surfactants are characterized according to the
"balance" between the hydrophilic ("water-
loving") and lipophilic ("oil-loving") portions of
their molecules.
• The hydrophilic-lipophilic balance (HLB) number
indicates the polarity of the molecules in an
arbitrary range of 1-40, with the most commonly
used emulsifiers having a value between 1 and 20.
• The HLB number increases with increasing
hydrophilicity.

43. Hydrophilic-Lipophilic Balance (HLB) System
• According to the HLB number, surfactants may be utilized for
different purposes:
Function HLB Range
Antifoaming agent 1 to 3
Emulsifier, water-in-oil 3 to 6
Wetting agent 7 to 9
Emulsifier, oil-in-water 8 to 18
Detergent 13 to 15
Solubilizer 15 to 20

44. Hydrophilic-Lipophilic Balance (HLB) System
• The desired HLB numbers can also be achieved by
mixing lipophilic and hydrophilic surfactants. The
overall HLB value of the mixture is calculated as the
sum of the fraction * individual HLB.
• Example: A mixture of 30% Span 80 (HLB=4.3) and
70% Tween 80 (HLB=15) has an overall HLB value
of:
HLB=(0.3 * 4.3) + (0.7 * 15)=11.8.

45. Methods of Preparation
• A mortar and pestle is employed frequently in the
extemporaneous preparation of emulsions. It is not a
very efficient technique and is not used on a large
scale. The types of equipment available for preparing
emulsions can be divided into four categories:
• (1) mechanical stirring
• (2) homogenizers
• (3) colloid mills
• (4) ultrasonifiers

46. Methods of Preparation
Mechanical Stirring:
• An emulsion may be stirred by means of various
impellers mounted on shafts, which are placed
directly into the system to be emulsified.
• The degree of agitation is controlled by the speed
of impeller rotation, but the patterns of liquid flow
and the resultant efficiency of mixing are
controlled by the type of impeller, its position in
the container, the presence of baffler, and the
general shape of the container.

49. Methods of Preparation
Homogenization:
• A homogenizer can be used to produce fine
droplets by first compressing the liquids to high
pressure and then allowing them to escape
gradually past a flat disc held by a strong spring.
• The high shearing stresses produced at pressure
ranging from 500-5000 p.s.i. can produce
extremely fine particles, the size depending on the
viscosity and the interfacial tension of a system.

51. Methods of Preparation
Colloid Mills:
• The colloid mills is used primarily for the reduction of
solid particle size and for the dispersion of suspensions
containing poorly wetted solids.
• Such a machine often is used when viscous emulsions are
to be prepared or when other methods are not available.
• The combination of rotator high speed, which produces
extremely high rates of shear, usually results in evolving
heat.

53. Methods of Preparation
Ultrasonification:
• The system works very well with fluid of moderate
viscosity, giving extremely fine particle size in
convenient.
• This technique is designed for commercial scale
production of pharmaceutical emulsions.

54. Pharmaceutical Applications
• Oral, rectal and topical administration
of oils and oils-soluble drugs.
• Intramuscular injections of some water-
soluble vaccines to provide slow release
and therefore a greater antibody
response and longer lasting immunity.
• Total parenteral nutrition (TPN) makes
use of an emulsion formulations. Sterile
oil-in-water emulsions are used to
deliver oily nutrients intravenously to
patients, using non-toxic emulsifying
agents.

55. Identification of Emulsion Type
• Miscibility Tests: an emulsion will mix
with a liquid that is miscible with the
continuous phase. Therefore an o/w
emulsion is miscible with water, a w/o
emulsion with an oil.
• Conductivity Measurement: systems
with an aqueous continuous phase will
conduct electricity, whilst systems with
an oily continuous phase will not.
• Staining Tests: filter paper soaked in
cobalt chloride solution and allowed to
dry turns from blue to pink on exposure
to stable o/w emulsions.