Pharmaceutical Compounding II

Lecture 6 Emulsion:Description, types, identification and

applications

Dr. Twana Mohammed M. Ways

2019-2020

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Outline of the lecture

• Description of emulsions

• Types of emulsion

• Identification of emulsion type

• Applications of emulsions in pharmacy

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• An emulsion is a dispersion of two immiscible (orpartially miscible) liquids, one of which is distributeduniformly in the form of fine droplets (the dispersedphase) throughout the other (the continuous phase).

• The immiscible liquids are oil or oily solution and water or aqueous solution.

• The system is stabilized by the presence of a thirdcomponent which is known as emulsifying agent.

Description of emulsions

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❑ Two main types of emulsion can exist;

➢ A product in which oil is dispersed as globules in water (an oil-in-water or o/w emulsion),

➢ and one in which water is dispersed as globules in the oilphase (a water-in-oil or w/o emulsion).

• In an o/w emulsion, the oil is sometimes referred to as theinternal phase the water being the external phase.

Types of emulsion according to the type of dispersed phase and dispersion medium

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Types of emulsion according to the type of dispersed phase and dispersion medium

Internal phase (water droplets)

External phase (oil phase)External phase (water phase)

Internal phase (oil droplets)

o/w emulsion w/o emulsion5

Multiple emulsions

• In multiple emulsions, o/w or w/o emulsions aredispersed in another liquid medium.

• Thus an oil-in-water-in-oil (o/w/o) consists of verysmall droplets of oil dispersed in the water globules ofa water-in-oil emulsion.

• The same for its counter part (w/o/w).

• Multiple emulsions have been proposed as potentialcandidates for sustained release dosage forms.

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Multiple emulsions

o/w/o w/o/w7

The aqueous phase

• The aqueous phase may contain water solubledrugs, preservative, colouring and flavouringagents.

• It is desirable to use distilled or deionised water,since calcium and magnesium ions, found in hardwater, can have an adverse effect on the stabilityof some emulsions; particularly those containingfatty acid soaps as emulsifying agent.

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The oil phase

• The oil phase of an emulsion frequentlyconsists of fixed or volatile oils, oil-solublevitamins, antiseptics and lipophilic drugs.

• It is often necessary to add an antioxidant toprevent autoxidation of the oil andconsequent rancidity and/or destruction ofany vitamin present.

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Identification of emulsion type

• It is important to know the type of an emulsion as this cansignificantly influence its application and properties.

• Generally an emulsion exhibits the characteristics of itsexternal (continuous) phase, and there are a number ofsimple tests based on this for distinguishing between o/wand w/o types of emulsion:

1. Water or oil miscibility2. Filter paper test3. Conductivity measurements4. Dye solubility test

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1. Water or oil miscibility

• An emulsion will only mix freely with a liquid that is misciblewith its continuous phase. Thus, a small quantity of waterdropped onto the surface of an o/w emulsion willimmediately mix with the external phase and disappear, but ifa small quantity of oil dropped on the emulsion two phaseswill form.

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1. Water or oil miscibility

• If a small quantity of oil is dropped onto a w/oemulsion, no phase change will be observed.However if water is added to the w/oemulsion, two phases of oil and water willform.

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2. Filter paper test

• The test involves putting a few drops of emulsiononto filter paper. If the droplet spreads rapidly intothe filter paper, it is an o/w emulsion, as water (theexternal phase) tends to spread more rapidlythroughout the filter paper than oil from a w/oemulsion.

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3. Conductivity measurements

• These are based on the principle that waterconducts electricity better than oils. Thusgenerally, o/w emulsions have a much higherelectrical conductivity than w/o emulsions.

• A light source will glow when electrodes(connected in series to a battery and suitablelight source) are dipped into an o/w emulsion,but not when they are placed in a w/o emulsion.

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3. Conductivity measurements

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4. Dye solubility tests

• These tests involve blending either a water soluble dye or an oil solubledye with the emulsion.

• If a water soluble dye (e.g. amaranth, red dye) is used, an o/w emulsionwill be evenly coloured, whereas a w/o emulsion will be much paler inappearance.

• Microscopically, an o/w emulsion will appear as colourless dropletsagainst a coloured (red if amaranth is used) background, whereas a w/oemulsion will appear as coloured (red) droplets against a colourlessbackground.

• If oil soluble dye (e.g. Scarlet red) is used, o/w emulsion will appear as reddroplets and the background will be colourless. However, w/o emulsionwill appear as colourless droplets against a red background.

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Water soluble dye (e.g. amaranth)

Oil soluble dye (e.g. Scarlet red)

o/w emulsion

w/o emulsion

Oil soluble dye (e.g. Scarlet red)

Water soluble dye (e.g. amaranth)

4. Dye solubility tests

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Applications of emulsions in pharmacy

• Emulsions can be formulated for virtually all themajor routes of administration, although mostcommercial products are developed for the oral,parenteral and topical routes.

• Oral and intravenous emulsions are generallyo/w type, whereas dermatological emulsions,and emulsions for subcutaneous or intramuscularinjection may also be formulated as w/oemulsions.

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• Medicinal o/w emulsions for oral administration are usedto deliver medicinal oils for the treatment of constipation(e.g. mineral oil, castor oil) and as oral food supplements(e.g. fish liver oils and vegetable oils) in a more palatableand acceptable form.

• The unpleasant taste of the oil is masked by the aqueousphase and any odour is suppressed when it is administeredas the internal phase of an o/w emulsion.

• Flavouring agents may be added to the external aqueousphase of the emulsion to increase the palatability.

Applications of emulsions in pharmacy: Oral emulsion

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• Oil-in-water emulsions containing vegetable oils are alsoused for the oral delivery of drugs and vitamins of lowaqueous solubility. Intestinal absorption is generallyenhanced when an oily solution of drug is presented in theform of small sub-micrometre oil droplets, because of thelarger interfacial area available for contact at theabsorption site.

• Absorption is also generally faster and more complete thanfrom suspension or tablet forms, because the drug in oralemulsions is already solubilized in the oil, thus eliminatingthe dissolution step prior to absorption.

Applications of emulsions in pharmacy: Oral emulsion

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• Sterile intravenous lipid o/w emulsions e.g.(Intralipid®) are used clinically as a source of caloriesand essential fatty acids for debilitated patients.

• o/w emulsions are also used as intravenous drugcarriers for drugs of limited water solubility;marketed products are available for drugs such asdiazepam, propofol, docetaxel and vitamin K.

Applications of emulsions in pharmacy: Intravenous emulsion

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• The advantages of intravenous emulsions oversolution formulations (in which the drug issolubilized by various co-solvents, and/or surfactantsand/or pH) include:

✓ a higher drug payload

✓ a lower toxicity

✓ less pain on injection

✓ and protection of labile drugs by the oilyenvironment

Applications of emulsions in pharmacy: Advantages of intravenous emulsion

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• Water-in-oil emulsions administered by the subcutaneous orintramuscular routes can be used to prolong the delivery of water-soluble antigens and thus provide a longer lasting immunity.

• Dermatological emulsions are the largest class of emulsions used inpharmacy, and range in consistency from structured fluids (lotions,liniments) to semisolids (creams).

• Both oil-in-water and water-in-oil emulsions are extensively used asvehicles to deliver drugs to the skin, and for their therapeuticproperties.

• Examples of topical emulsions are estradiol and betamethasone.

Applications of emulsions in pharmacy

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Thanks

Questions?

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