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Defn Emulsion
 An emulsion is a coarse dispersion in which the dispersed phase is composed of small globules of a liquid distributed throughout a vehicle in which it is immiscible.
-In emulsion terminology the dispersed phase is referred to as the internal phase, and the dispersion medium as the external or continuous phase.
-O/W is water is the external phase. W/O if oil is the external phase
What is and Emulsifying agent and what is it used for?
*Emulsifying agent is the third component of an emulsion system and its purpose is to facilitate the dispersion of and the maintenance of the internal phase. The need for an emulsifying agent is as follows:  emulsions are thermodynamically unstable because of the large increase in interfacial area and hence large surface free energy. Hence they will naturally tend towards the reduction of this area by droplet merger.
 Furthermore, the difference in the density of the two phases will make the emulsion to cream (i.e., the less dense phase rises; while the more dense phase falls in the container). Subsequently, the droplets can coalesce with a considerable reduction in surface area and hence surface energy.
- Some act as surfactants
-May be prepared as solid or liquid
-liquid emulsions may be employed orally, topically, or parenterally; semi¬solid emulsions, topically. Many pharmaceutical preparations that may actually be emulsions may not be classified as such because they fit some other pharmaceutical category more appropriately
What is the purpose of an emulsion?
To mix oil and water
Why Prepare Emulsions?
1)     Pharmaceutically, the process of emulsification enables the pharmacist to prepare relatively stable and homogeneous mixtures of two immiscible liq­uids.
(2) It permits the administration of a liquid drug in the form of minute globules rather than in bulk. For orally administered emulsions, the oil-in-water type of emulsion permits the palatable administra¬tion of an otherwise distasteful oil by dispersing it in a sweetened, flavored aqueous vehicle in which it may be carried past the taste buds and into the stomach.
3) The reduced particle size of the oil glob¬ules may render the oil more digestible and more readily absorbed, or if that is not the intent, more effective in its task, as for example the increased ef¬ficacy of mineral oil as a cathartic when in the emulsified form

Cream---almost all are oil in water to make it easily washable.Ointment-water in oil
Oral Emulsion are oil in water to prevent GI-Irritation
(4)     Emulsions to be applied externally to the skin may be prepared as o/w or w/o emulsions. Medicinal agents that are irritating to the skin generally are less irritating if present in the internal phase of an emulsified top­ical preparation than in the external phase from which direct contact with the skin is more preva­lent.
(5) If it is desirable to have a preparation that is more easily removed from the skin with wa¬ter, an oil-in-water emulsion would be preferred. As for absorption, absorption through the skin (percutaneous absorption) may be enhanced by the diminished particle size of the internal phase.
What are some formulation consideration in designing an Emulsion?
(A) Choosing the appropriate type of emulsion (o/w or w/o)
i. Oral emulsions: They are generally made as o/w for palatability reasons since the external water phase can be flavored or sweetened.
ii. Topical emulsions may be o/w or w/o depending on the purpose:
Ø      w/o emulsion have good emollient property but the product cannot be easily washed from the body.
Ø      o/w emulsion can be easily washed off and is more esthetically pleasing to most users.

iii. Parenteral emulsions for intravenous (IV) use are made as o/w for miscibility with blood. For example IV lipids are commercially available as 10% or 20% emulsions derived from soybean oil (Intralipid) or a combination of soybean oil and safflower oil (Liposyn II). Both the 10% or 20% emulsions are isotonic and can be administered via the peripheral vein. They contain 1.2% egg yolk phospholipids as the emulsifying agent and 2.25 to 2.5% glycerol to make the emulsions isoosmotic.
"iv. Emulsions for intramuscular administration may be either o/w or w/o depending upon the rapidity of response desired. It is believed that water soluble drugs are released from injection site more rapidly from o/w than w/o emulsions. O/W is release
faster."

v. Complex emulsions (o/w/o or w/o/w) emulsions have been designed for controlled drug delivery systems
What are some desirable properties of an emulsifying agent?
 be surface active and reduce interfacial tension considerably
 be adsorbed quickly around the dispersed droplets as a condensed film which will prevent coalescence
 impart charges/electrical potential to the droplets so that mutual repulsion can occur
 increase the viscosity of the emulsion
 be effective in reasonably low concentration
 it must be compatible with the other formulation in¬gredients and must not interfere with the stability or efficacy of the therapeutic agent.
 It should be stable and not deteriorate in the preparation.
 The emulsifier should be nontoxic with respect to its in¬tended use and the amount to be consumed by the patient. Also, it should possess little odor, taste, or color.
 Of prime importance is the capability of the emulsifying agent to promote emulsification and to maintain the stability of the emulsion for the in¬tended shelf-life of the product.
How are Emulsions classified?
Emulsifying agents may be classified in accordance with the type of film they form at the interface between the two phases.
What is Monomolecular film?
—Those surface-active agents that are capable of stabilizing an emulsion do so by forming a monolayer of adsorbed molecules or ions at the oil—water in­terface (See the figure below). This results in a more stable emulsion because of a proportional reduction in the interfacial tension and hence surface free energy. This reduction is probably not the main factor promot­ing stability. More significant is the fact that the droplets are surrounded now by a coherent monolayer that prevents coales­cence between approaching droplets. If the emulsifier forming the monolayer is ionized, the presence of strongly charged and mutually repelling droplets increases the stability of the sys­tem. With un-ionized, nonionic surface-active agents, the particles may still carry a charge; this arises from adsorption of a specific ion or ions from solution.
Multimolecular films?
Hydrated lyophilic colloids form multimolecular films around droplets of dispersed oil. The use of these agents has declined in recent years because of the large number of synthetic surface-active agents available that possess well-marked emulsifying proper­ties. Although these hydrophilic colloids are adsorbed at an interface (and can be regarded therefore as surface active), they do not cause an appreciable lowering in surface tension. Rather, their efficiency depends on their ability to form strong coherent multimolecular films. These act as a coating around the droplets and render them highly resistant to coalescence even in the absence of a well-developed surface potential. Fur­thermore, any hydrocolloid not adsorbed at the interface in­creases the viscosity of the continuous aqueous phase; this also enhances emulsion stability.
Solid particle Film?
mall solid particles that are wetted to some degree by both aqueous and nonaqueous liquid phases act as emulsifying agents. If the particles are too hy­drophilic, they remain in the aqueous phase; if too hydrophobic, they are dispersed completely in the oil phase. A second re­quirement is that the particles are small in relation to the droplets of the dispersed phase.
How do you determine what Emulsion type you made? What tests do you perform?
a) Dilution test—The dilution method depends on the fact that an O/W emulsion can be diluted with water and a W/O emulsion with oil. When oil is added to an O/W emulsion or water to a W/O emulsion, the additive is not incorporated into the emulsion and separation is apparent. The test is greatly improved if the addition of the water or oil is observed microscopically.

(b) Conductivity test—An emulsion in which the continuous phase is aqueous can be expected to possess a much higher conductivity than an emulsion in which the continuous phase is an oil. Accordingly, it frequently happens that when a pair of electrodes, connected to a lamp and an electrical source are dipped into an O/W emulsion, the lamp lights because of the passage of a current between the two electrodes. If the lamp does not light, it is assumed that the system is W/O

(c) Dye-solubility test—The knowledge that a water-soluble dye will dissolve in the aqueous phase of an emulsion while an oil-soluble dye will be taken up by the oil phase provides a third means of determining emulsion type. Thus, if microscopic examination shows that a water-soluble dye has been taken up by the continuous phase, we are dealing with an O/W emulsion. If the dye has not stained the continuous phase, the test is repeated using a small amount of an oil-soluble dye. Coloring of the continuous phase confirms that the emulsion is of the W/O type.

(d) Fluorescence method: Since oils fluoresce under UV light, o/w emulsions will exhibit dot pattern; while w/o emulsions will show continuous fluorescence.


(e) Bancroft’s rule: Whether the emulsion will be O/W or W/O can be determined from Bancroft’s rule, which states that the phase in which the emulsifying agent is more soluble will be the external phase.
Defn a Dilution test
The dilution method depends on the fact that an O/W emulsion can be diluted with water and a W/O emulsion with oil. When oil is added to an O/W emulsion or water to a W/O emulsion, the additive is not incorporated into the emulsion and separation is apparent. The test is greatly improved if the addition of the water or oil is observed microscopically.
What is a conductivity test?
An emulsion in which the continuous phase is aqueous can be expected to possess a much higher conductivity than an emulsion in which the continuous phase is an oil. Accordingly, it frequently happens that when a pair of electrodes, connected to a lamp and an electrical source are dipped into an O/W emulsion, the lamp lights because of the passage of a current between the two electrodes. If the lamp does not light, it is assumed that the system is W/O
What is a Dye Solubility test?
The knowledge that a water-soluble dye will dissolve in the aqueous phase of an emulsion while an oil-soluble dye will be taken up by the oil phase provides a third means of determining emulsion type. Thus, if microscopic examination shows that a water-soluble dye has been taken up by the continuous phase, we are dealing with an O/W emulsion. If the dye has not stained the continuous phase, the test is repeated using a small amount of an oil-soluble dye. Coloring of the continuous phase confirms that the emulsion is of the W/O type.
What is a Flurescence Method Test?
Since oils fluoresce under UV light, o/w emulsions will exhibit dot pattern; while w/o emulsions will show continuous fluorescence.
Bancroft's Rule test?
: Whether the emulsion will be O/W or W/O can be determined from Bancroft’s rule, which states that the phase in which the emulsifying agent is more soluble will be the external phase.
What are the two stability forms of Emulsion?
Chemical stability and physical stability
How do you know an emulsion is chemically stable?
If the emulsified product is to have some antimicrobial activity (eg, a medicated lotion), care must be taken to ensure that the formulation possesses the required degree of activity. Frequently, a compound exhibits a lower antimicrobial activity in an emulsion than, say, in a solution. Generally, this is because of partitioning effects between the oil and water phases, which cause a lowering of the effective concentration of the active agent. Partitioning has also to be taken into account when considering preservatives to prevent microbiological spoilage of emulsions. Finally, the chemical stability of the various components of the emulsion should receive some attention, as such materials may be more prone to degradation in the emulsified state than when they exist as a bulk phase.
How do you know and emulsion is physically stable?
In the present discussion, detailed consideration will be limited to the question of physical stability. The three major phenomena associated with physical stability are
1. The upward or downward movement of dispersed droplets relative to the continuous phase,
termed creaming or sedimentation, respectively.
2. The aggregation and possible coalescence of the dispersed droplets to reform the separate, bulk phases.
3. Inversion, in which an O/W emulsion inverts to become a WIO emulsion and vice versa.
Defn Creaming
Creaming is the upward movement of dispersed droplets relative to the contin¬uous phase;
Defn Sedimentation
Sedimention is the downward movement of dispersed droplets relative to the contin¬uous phase;creaming, or sedimentation, brings the particles closer together and may facilitate the more serious problem of
coalence
What the formula for Stoke's Law
V = 2r2(p — p0)g/9ηo
What is Stoke's law good for?
Stokes’ equation is still useful because it points out the factors that influence the rate of sedimentation or creaming. These are the diameter of the suspended droplets, the viscosity of the dispersion medium, and the difference in densities between the dispersed phase and the dispersion medium. Usually, only the use of the first two factors is feasible in affecting creaming or sedimentation. Reduction of particle size contributes greatly toward overcoming or minimizing creaming, because the rate of movement is a square-root function of the particle diameter. There are, however, technical difficulties in reducing the diameter of droplets to below about 0.1 m. The most frequently used approach is to raise the viscosity of the continuous phase, although this can be done only to the extent that the emulsion still can be removed readily from its container and spread or administered conveniently.
Define Aggregation
Stokes’ equation is still useful because it points out the factors that influence the rate of sedimentation or creaming. These are the diameter of the suspended droplets, the viscosity of the dispersion medium, and the difference in densities between the dispersed phase and the dispersion medium. Usually, only the use of the first two factors is feasible in affecting creaming or sedimentation. Reduction of particle size contributes greatly toward overcoming or minimizing creaming, because the rate of movement is a square-root function of the particle diameter. There are, however, technical difficulties in reducing the diameter of droplets to below about 0.1 m. The most frequently used approach is to raise the viscosity of the continuous phase, although this can be done only to the extent that the emulsion still can be removed readily from its container and spread or administered conveniently.
Define Coalescence
Coales¬cence, the complete fusion of droplets, leads to a decrease in the number of droplets and the ultimate separation of the two immiscible phases (cracking). Aggregation precedes coalescence in emulsions. Aggregation is, to some extent, reversible; however, cracking is not reversible.
What is Inversion and what factors cause it?
An emulsion is said to invert when it changes from O/W to a W/O emulsion, or vice versa.
i) Inversion sometimes can be brought about by the addition of an electrolyte. For example, an O/W emulsion having sodium stearate as the emulsifier can be inverted by the addition of calcium chloride because the calcium strearate formed is a lipohilic emulsifier and favors the formation of a W/O product.
ii) Or by changing the phase-volume (volume of the internal phase divided by the volume of the emulsion) ratio.
iii) Inversion often can be seen when an emulsion, prepared by heating and mixing the two phases, is being cooled. This takes place because of the temperature-dependent changes in the solubilities of the emulsifying agents.
What are Opthalmic Preparations used for?
Drugs are applied to the eye for the localized effect of the medication on the surface of the eye or on its interior. Most frequently aqueous solutions are employed; however, suspensions, and ophthalmic ointments are also used. Recently, ophthalmic inserts, impregnated with drug, have been developed to provide for the continuous release of medication.
What Volume of Opthalmic solution is administered and how is it determined?
The normal volume of tears in the eye is 7μL. Whereas a non-blinking eye can accommodate a maximum of 30μL of fluid, blinking eyes can hold only 10μL. Excessive liquids, both normally produced and externally added, are rapidly drained from the eye. Therefore, the usual single drop size of an instilled drug solution may be 50 μL and thus, much of the drop instilled may be lost. The effective “dose” of medication administered ophthalmically may be varied by the strength of medication administered, the volume administered, the retention time of the medication in contact with the surface of the eye and the frequency of administration.
What are some thing you should consider in preparing an opthalamic solution?
Considerations in the preparation of ophthalmic solutions includes sterility, preservation, isotonicity, buffering, viscosity and appropriate packaging.
What are some sterility considerations?
All ophthalmic solutions should be sterile when dispensed and wherever possible, a suitable preservative should be added to ensure sterility during the course of the use. Ophthalmic solution intended to be used during surgery generally do not contain preservative agents because these are irritating to the tissues within the eye. These solutions are usually packaged in single-dose containers and any unused solution discarded.