SPIRITS

SPIRITS

Definition:

Spirits are alcoholic or hydroalcoholic solutions of volatile substances. Most are used as flavoring agents but a few have medicinal value. The active ingredient in the spirit may be a solid, liquid or gas.

Use:

(i)       They are mainly used as flavoring agents. e.g. Lemon spirit, Peppermint Spirit, Compound Orange Spirit etc.

(ii)     Some spirits are taken internally for their medicinal value e.g. Aromatic Spirit of Ammonia IP is a respiratory stimulant.

Storage:

Spirits contains volatile substances hence, should be stored in tight containers and should be stored in a cool place. This prevents the volatilization of alcohol or the active substances.

Methods of preparation:

(i)      Simple solution method        e.g. Chloroform Spirit IP               Spirit of Ether IP

(ii) Solution with maceration       e.g. Compound Orange Spirit IP

(iii) Distillation        e.g. Aromatic Spirit of    Ammonia IP

Examples:

Name of Spirit	Formula	Method of preparation
Chloroform Spirit IP	Chloroform 50ml Alcohol (90%v/v) upto 1000ml	Simple solution
Spirit of Ether IP	Anaesthetic Ether 330ml Alcohol (90%v/v) up to 1000ml	Simple solution

Aromatic Spirit of Ammonia

Synonym.  Aromat. Sp. Ammon.,     Spirit of Sal Volatile

Formula:               Ammonium bicarbonate [NH₄HCO₃]             25g

                                Ammonia solution strong                                  70ml

                                Lemon oil                                                              5ml

                                Nutmeg oil                                                            3ml

                                Alcohol (90%v/v)                                                750ml

                                Purified Water q.s.                                               1000ml

Method of preparation:

(i)       Lemon oil (5ml) + Nutmeg oil (3ml) + Alcohol 90% (750ml) + Purified Water (375ml) ® taken in a still (1173ml)

(ii)     The first 875ml portion of the distillate is collected.

(iii)    The second 35ml portion of the distillate is collected separately.

(iv)   The second distillate is taken in a bottle, ammoniumbicarbonate (25g) and strong ammonia solution (70ml) is taken. The bottle is closed and warmed gently at 60⁰C on a water bath. The bottle is shaken to dissolve the salt completely.

(v)     The solution is cooled and filtered through cotton wool.

(vi)   This solution is then mixed gradually with the first distillate (i.e. 875ml).

(vii)  Sufficient purified water is added to make up the volume up to 1000ml.

Storage:

The preparation contains volatile oils (Nutmeg and Lemon oil) therefore, it should be stored in a tightly closed container in a cool place.

Differences between pastes and ointments

Differences between pastes and ointments

(i)     Pastes generally contains a large amount (50%) of finely powdered solids. So they are often stiffer than ointments.

(ii)   When applied to the skin pastes adhere well, forming a thick coating protects and soothes inflamed and raw surfaces and minimizes the damage done by scratching in itchy conditions such as chronic eczema. it is comparatively easy to confine pastes to the diseased  areas whereas ointments, which are usually less viscous, tend to spread on to healthy skin, and this may result in sensitivity reactions if the preparations contain a powerful medicament such as dithranol.

(iii) Because of the powder contents pastes are porous; hence, perspiration can escape. Since the powders absorbs exudate, pastes with hydrocarbon base are less macerating than ointments with a similar base.

(iv) They are less greasy than ointments but since their efficacy depends on maintaining a thick surface layer they are far from attractive cosmetically.

(v)   Most of the pastes are unsuitable for treating scalp conditions because they are difficult to remove from the hair.

OINTMENT & Preparation Of Ointments

OINTMENT

Definition: Ointments are semisolid preparations for application to the skin or mucosae. The ointment bases are almost always anhydrous and generally contains one or more medicaments in suspension or solution.

Characteristics of an ideal ointment:

1.      It should be chemically and physically stable.

2.      It should be smooth and free from grittiness.

3.      It should melt or soften at body temperature and be easily applied.

4.      The base should be non-irritant and should have no therapeutic action.

5.      The medicament should be finely divided and uniformly distributed throughout the base.

Classification of ointments

According to their therapeutic properties based on penetration of skin.

According to their therapeutic uses.

Ointments classified according to their therapeutic properties based on penetration are as follows:

(a) Epidermic, (b) Endodermic, (c) Diadermic

Preparation Of Ointments

A well-made ointment is -

(a) Uniform throughout i.e. it contains no lumps of separated high melting point ingredients of the base, there is no tendency for liquid constituents to separate and insoluble powders are evenly dispersed.

(b) Free from grittiness, i.e. insoluble powders are finely subdivided and large lumps of particles are absent. Methods of preparation must satisfy this criteria.

Two mixing techniques are frequently used in making ointments:

1. Fusion, in which ingredients are melted together and stirred to ensure homogeneity.

2. Trituration, in which finely-subdivided insoluble medicaments are evenly distributed by grinding with a small amount of the base or one of its ingredients followed by dilution with gradually increasing amounts of the base.

1. Ointments prepared by Fusion method:

When an ointment base contain a number of solid ingredients such as white beeswax, cetyl alcohol, stearyl alcohol, stearic acid, hard paraffin, etc. as components of the base, it is required to melted them. The melting can be done in two methods:

Method-I

The components are melted in the decreasing order of their melting point i.e. the higher m.p. substance should be melted first, the substances with next melting point and so on. The medicament is added slowly in the melted ingredients and stirred thoroughly until the mass cools down and homogeneous product is formed.

Advantages:

This will avoid over-heating of substances having low melting point.

Method-II

All the components are taken in subdivided state and melted together.

Advantages:

The maximum temperature reached is lower than Method-I, and less time was taken possibly due to the solvent action of the lower melting point substances on the rest of the ingredients.

Cautions:

(i)     Melting time is shortened by grating waxy components (i.e. beeswax, wool alcohols, hard-paraffin, higher fatty alcohols and emulsifying waxes) by stirring during melting and by lowering the dish as far as possible into the water bath so that the maximum surface area is heated.

(ii)   The surface of some ingredients discolors due to oxidation e.g. wool fats and wool alcohols and this discolored layers should be removed before use.

(iii) After melting, the ingredients should be stirred until the ointment is cool, taking care not to cause localized cooling, e.g. by using a cold spatula or stirrer, placing the dish on a cold surface (e.g. a plastic bench top) or transferring to a cold container before the ointment has fully set. If these precautions are ignored, hard lumps may separate.

(iv) Vigorous-stirring, after the ointment has begun to thicken, causes excessive aeration and should be avoided.

(v)   Because of their greasy nature, many constituents of ointment bases pickup dirt during storage, which can be seen after melting. This is removed from the melt by allowing it to sediment and decanting the supernatant, or by passage through muslin supported by a warm strainer. In both instances the clarified liquid is collected in another hot basin.

(vi) If the product is granular after cooling, due to separation of high m.p. constituents, it should be remelted, using the minimum of heat, and again stirred and cooled.

Example:

(i) Simple ointment B.P. contains

                                                Wool fat                      50g

                                                Hard paraffin               50g

                                                Cetostearyl alcohol      50g

                                                White soft paraffin      850g

Type of preparation:                Absorption ointment base

Procedure:

Hard paraffin and cetostearyl alcohol on water-bath. Wool fat and white soft paraffin are mixed and stirred until all the ingredients are melted.

If required decanted or strained and stirred until cold and packed in suitable container.

(ii) Paraffin ointment base

Type of preparation : Hydrocarbon ointment base

(iii) Wool alcohols ointment B.P.

Type of preparation: Absorption base

(iv) Emulsifying ointment B.P.

Type of preparation: Water-miscible ointment base.

(v) Macrogol ointment B.P.C

Type of preparation: Water soluble ointment base

Formula:         Macrogol 4000

                        Liquid Macrogol 300

Method: Macrogol 4000 is melted and previously warmed liquid macrogol 300 is added. Stirred until cool.

2. OINTMENT PREPARED BY TRITURATION

This method is applicable in the base or a liquid present in small amount.

(i)     Solids are finely powdered are passed through a sieve (# 250, # 180, #125).

(ii)   The powder is taken on an ointment-slab and triturated with a small amount of the base. A steel spatula with long, broad blade is used. To this additional quantities of the base are incorporated and triturated until the medicament is mixed with the base.

(iii) Finally liquid ingredients are incorporated. To avoid loss from splashing, a small volume of liquid is poured into a depression in the ointment an thoroughly incorporated before more is added in the same way. Splashing is more easily controlled in a mortar than on a tile.

Example:

(i) Whitfield ointment (Compound benzoic acid ointment B.P.C.)

Formula:         Benzoic acid, in fine powder   6gm

                        Salicylic acid, in fine powder  3gm

                        Emulsifying ointment              91gm

Method: Benzoic acid and salicylic acid are sieved through No. 180 sieves. They are mixed on the tile with small amount of base and levigated until smooth and dilute gradually.

(ii) Salicylic acid sulphur ointment B.P.C.

3. OINTMENT PREPARATION BY CHEMICAL REACTION

Chemical reactions were involved in the preparation of several famous ointments of the past, e.g. Strong Mercuric Nitrate Ointment, both of the 1959 B.P.C.

(a) Ointment containing free iodine

Iodine is only slightly soluble in most fats and oils but readily soluble.

Iodine is readily soluble in concentrated solution of potassium iodide due to the formation of molecular complexes KI.I₂, KI.2I₂, KI.3I₂ etc.

These solutions may be incorporated in absorption-type ointment bases. 

e.g. Strong Iodine Ointment B.Vet.C (British Veterinary Pharmacopoeia) is used to treat ringworm in cattle. It contains free iodine. At one time this type of ointments were used as counter-irritants in the treatment of human rheumatic diseases but they were not popular because:

(i)     They stain the skin a deep red color.

(ii)   Due to improper storage the water dries up and the iodine crystals irritate the skin, hence glycerol was some times to dissolve the iodine-potassium iodide complex instead of water.

Example: Strong Iodine Ointment B. Vet.C.

                        Iodine

                        Woolfat

                        Yellow soft paraffin

                        Potassium iodide

                        Water

Procedure:

(i)     KI is dissolved in water. I₂ is dissolved in it.

(ii)   Woolfat and yellow soft paraffin are melted together over water bath. Melted mass is cooled to about 40⁰C.

(iii) I₂ solution is added to the melted mass in small quantities at a time with continuos stirring until a uniform mass is obtained.

(iv) It is cooled to room temperature and packed.

Use: - Ringworm in cattle.

(b) Ointment containing combined iodine

Fixed oils and many vegetable and animal fats absorb iodine which combines with the double bonds of the unsaturated constituents, e.g.

CH₃.(CH₂) ₂.CH = CH.(CH₂) ₇.COOH + I₂ ® CH₃.(CH₂) ₂.CHI CHI.(CH₂) ₇.COOH

                                    Oleic acid                                            di-iodostearic acid

Example: Non-staining Iodine Ointment B.P.C. 1968              Iodine

                                                                                                Arachis Oil

                                                                                                Yellow Soft Paraffin

Method:

(a)    Iodine is finely powdered in a glass mortar and required amount is added to the oil in a glass-stoppered conical flask and stirred well.

(b)   The oil is heated at 50⁰C in a water-bath and stirred continually. Heating is continued until the brown color is changed to greenish-black; this may take several hours.

(c)    From 0.1g of the preparation the amount of iodine is determined by B.P.C. method and the amount of soft paraffin base is calculated to give the product the required strength.

(d)   Soft paraffin is warmed to 40⁰C. The iodized oil is added and mixed well. No more heat is applied because this causes deposition of a resinous substance.

(e)    The preparation is packed in a warm, wide-mouthed, amber color, glass bottle. It is allowed to cool without further stirring.

4. PREPARATION OF OINTMENTS BY EMULSIFICATION

An emulsion system contain an oil phase, an aqueous phase and an emulsifying agent.

For o/w emulsion systems the following emulsifying agents are used:

            (i) water soluble soap

            (ii) cetyl alcohol

            (iii)glyceryl monostearate

            (iv) combination of emulsifiers: triethanolamine stearate + cetyl alcohol

            (v) non-ionic emulsifiers: glyceryl monostearate, glyceryl monooelate, propylene glycol stearate

For w/o emulsion creams the following emulsifiers are used:

            (i) polyvalent ions e.g  magnesium, calcium and aluminium are used.

            (ii) combination of emulsifiers: beeswax + divalent calcium ion

The viscosity of this type of creams prevent coalescence of the emulsified phases and helps in stabilizing the emulsion.

Example:

Cold cream:

Procedure:

(i)     Water immiscible components e.g. oils, fats, waxes are melted together over water bath (70⁰C).

(ii)   Aqueous solution of all heat stable, water soluble components are heated (70⁰C).

(iii) Aqueous solution is slowly added to the melted bases with continuous stirring until the product cools down and a semi-solid mass is obtained.

N.B. The aqueous phase is heated otherwise high melting point fats and waxes will immediately solidify on addition of cold aqueous solution.

Introduction to biopharmaceutics and pharmacokinetics

Definition of Biopharmaceutics

Biopharmaceutics can be defined as the study of the

interrelationship of the physicochemical properties of the drug,

the dosage form in which the drug is given,

and the route of administration

on the rate and extent (amount) of systemic drug absorption.

Thus biopharmaceutics deals with the factors that influence the

1.       protection of the activity of the drug within the drug product (stability)

2.       the release of the drug from the a drug product

3.       the rate of dissolution of the drug at the absorption site, and

4.       the systemic absorption of the drug.

Studies of biopharmaceutics involves both in-vitro and in-vivo methods.

In-vitro methods involves test apparatus without involving laboratory animals or humans. E.g. disintegration tests, dissolution tests etc.

In-vivo test involves measurement of systemic drug availability (bioavailability) after giving a drug product to an animal or human. 

Definition of Pharmacokinetics

Pharmacokinetics is defined as the study of rate processes involved in absorption, distribution, metabolism and excretion (ADME).

The study of pharmacokinetics involves both experimental and theoretical approaches.

The experimental approach involves

1.       the development of biological sampling techniques

2.       analytical methods development for the measurement of drugs and metabolites

3.       and the procedures for data collection and manipulation.

The theoretical aspect of pharmacokinetics involves the development of pharmacokinetic models that predicts drug disposition after drug administration.

The application of statistics is an integral part of pharmacokinetic models top determine data errors, deviation of models and correlation.

Clinical pharmacokinetics is the application of pharmacokinetic methods in drug therapy.

This is a multidisciplinary approach where the dose of a drug is optimized for a specific patient depending on the disease state, age and sex of the patient. This subject requires information from medical and pharmaceutical research.

Population pharmacokinetics is the study of pharmacokinetic differences of drug in various population groups.

Therapeutic drug monitoring (TDM)

When drug with narrow therapeutic indices are used in patients, it is necessary to monitor plasma drug concentration closely by taking periodic blood samples. Some drugs those are frequently monitored are aminoglycoside antibiotics, convulsants and anticancer drugs in order to minimize adverse side effects.

Pharmacodynamics deals with the relationship between the drug concentration at the site of action (receptor) and pharmacologic response, including biochemical and physiological effects that influence the interaction of drug with the receptor.

Under pharmacodynamics we study the relationship between the plasma concentration of drug (related to the concentration at the site of action) and the magnitude of biological effect it shows.

Toxicokinetics

Toxicokinetics is the application of pharmacokinetic principles to the design, conduct and interpretation of drug safety evaluation studies and used in validating dose related exposure in animals. Toxicokinetic studies are conducted in animals and the result obtained is used to interpret possible toxic reactions in human.

The ultimate aim of a drug is to achieve optimal therapy.

1.       To attain this aim the drug is first molded into a suitable dosage form.

2.       The dosage form is administered in to the body through a suitable route of administration.

3.       The drug is released at the site of absorption at a certain rate.

4.       The drug is then absorbed from the site of absorption to systemic circulation.

5.       The drug is carried to various tissues through blood. The drug is distributed to extravascular tissues. The distribution method is a reversible process. The drug returns back to the systemic circulation.

6.       The drug produces its action at the site of action. The site of action may reside in some extravascular tissues.

7.       The drug is excreted through kidney and metabolize in the liver and various tissues. Thus the drug is eliminated from the body.

All the above processes are occurring at a certain rate. Under the subject pharmacokinetics we study those rates and built up equations to predict those rate processes.

Application of biopharmaceutics

1.       A company is going to market a new dosage form of a certain drug. The dose is known. When this dosage form is administered to a healthy human the drug may not released quickly. In this case the action of the drug will be delayed. In another case if the drug is released all at a time then the duration of action of the drug will be very short. So with the knowledge of biopharmaceutics we can change various formulation factors to obtain optimum onset of action and duration of action.

2.       A company is marketing tablets of a certain drug. Now it wants to change a few ingredients or some formulation factors. The new tablets may not behave similarly as the previous one. So the bioavailability of new tablets are compared with the old tablets. If it is found that the bioavilability of the newer tablets are equivalent (i.e bioequivalent)  to that of older tablets then the new tablets will be permitted to market (by FDA).

3.       A company is marketing the tablets of a certain drug. Now they have planned to make transdermal dosage form of the same drug. To establish its efficacy the bioavailability of the transdermal dosage form is compared to that of the established tablet dosage form. If both are found to be closer then the transdermal dosage form will be accepted by FDA.

Application of pharmacokinetics

1.       The bioavailabilty of a dosage form is calculated by pharmacokinetic equations.

2.       The frequency of dosing is calculated from pharmacokinetic equations.

3.       To calculate the dose of a controlled release dosage form pharmacokinetic equations are required.

4.       In case of patients with kidney failure the dose of a drug should be calculated very cautiously. If the rate of absorption of the drug is greater than the elimination rate of the drug from that patient then the drug will be accumulated in the body and may show toxic effect. The rate of elimination of the drug from the body of that patient is calculated with the help of pharmacokinetic equations.

5.       When a potent anticancer drug is administered to a patient the plasma concentration of the drug must be very close to minimum effective concentration. Since the therapeutic index of the drug is very narrow in case of potent drugs so rate of administration must also be very slow. This rate of administration is calculated by pharmacokinetic principles.

BIPHASIC LIQUID DOSAGE FORMS

BIPHASIC LIQUID DOSAGE FORMS

Additives used in suspension dosage forms

1. Wetting agents: Some substances (e.g. sulfur, hydrocortisone etc.) are both insoluble in water and are poorly wetted by it. During preparation it is difficult to disperse the clumps and the foam produced on shaking. So wetting agents are used to reduce the interfacial tension between the solid particle and the vehicle and increase wetting of the particle.

e.g.    alcohol,  glycerin, propylene glycols, saponins of quillaia extract etc.

2. Flocculating agents: On standing for a long period the suspension may become difficult to redisperse on shaking. That time, controlled flocculation is required to prevent compact sediment, which is difficult to redisperse. Controlled flocculation can be produced either by,
(i) electrolytes (e.g. potassium citrate, phosphate salts), (ii) surfactants, and (iii) polymers.

3. Suspending agents / Thickening agents: Suspending agents are the substances, which are added to a suspension to increase the viscosity of the continuous phase so that the particles remain suspended for a sufficiently long time and it becomes easy to measure an accurate dose.

                                Due to increase in viscosity of the vehicle, the particles sediment at a much slower rate.

                                e.g. methylcellulose, hydroxy propyl methyl cellulose, sodium carboxymethylcellulose, bentonite, veegum etc.

4. Preservative: The aqueous vehicle may be liable for bacterial growth, so a preservative should be used. e.g. benzoic acid, sodium benzoate, methylparaben, proptlparaben etc. may be used.

5. Organoleptic additives: Colors, sweeteners and flavoring agents may be used to make the oral suspensions more palatable.

                                      Colors:             e.g. Amaranth, Tartrazine, Caramel, and other approved colors

                                      Sweeteners:     e.g. Sucrose

                                      Flavors:           e.g. Peppermint oil, Chocolate flavor, Raspberry syrup etc.

Additives used in emulsion dosage forms

A. Emulsifying agent: The emulsifying agents stabilize an emulsion by various mechanisms. They are also known as emulgents or emulsifiers.

Classification of emulsifiers:

Type	Examples	Mode of action
Hydrophilic colloids	Vegetable source Gum acacia Tragacanth Starch Animal source Wool fat Egg yolk Gelatin Synthetic Methyl cellulose, Hydroxyethyl cellulose,	(i)       They do not reduce the surface tension but forms a rigid film on the oil droplets and form a stable o/w emulsion - thus inhibits coalescence of droplets. (ii)     As an auxiliary emulsifier they increase the viscosity of the continuous phase so that movement of dispersed phase is reduced.
Finely divided solid particles	Colloidal clays: bentonite (aluminium silicate) veegum (magnesium aluminium silicate).	(i)       They tend to absorb at the oil-water-interface and form thick impenetrable films. (ii)     Sometimes increases the viscosity of water (as continuous phase).
Synthetic Surface Active Agents	Anionic Potassium stearate Sodium lauryl sulphate Cationic Cetyl trimethyl ammonium bromide (or cetrimide) Ampholytic N-dodecyl alanine Non-ionic Sorbitan mono-oleate (TWEEN) Polyoxyethylene sorbitan mono-oleate (Polysorbate)	(i)       They form a flexible film on the oil-water interface. (ii)     They lower interfacial tension markedly and this contribute to the stability of emulsion. (iii)    In case of ionic surfactants surface charge is developed, increasing the zeta-potential, which will cause repulsion between two adjacent globules.

Difference between emulsion and suspension

Emulsions	Suspensions
1.       They contain two immiscible liquids, one of which is dispensed as minute globules into the other. 2.       Emulsifying agents are required to make a stable emulsion. 3.       Emulsions are mainly of two types: o/w and w/o. 4.       During storage, freezing should be avoided as it may lead to cracking of emulsion.	1.       They contain finely divided solid particles dispersed in a liquid or semisolid vehicle. 2.       Suspending agents are required to make a stable suspension. 3.       Suspensions are mainly of two types: (i) Flocculated and (ii) De-flocculated. 4.       During storage, freezing should be avoided as it may lead to aggregation of suspended particles.

BIPHASIC LIQUID DOSAGE FORMS

BIPHASIC LIQUID DOSAGE FORMS

Additives used in suspension dosage forms

1. Wetting agents: Some substances (e.g. sulfur, hydrocortisone etc.) are both insoluble in water and are poorly wetted by it. During preparation it is difficult to disperse the clumps and the foam produced on shaking. So wetting agents are used to reduce the interfacial tension between the solid particle and the vehicle and increase wetting of the particle.

e.g.    alcohol,  glycerin, propylene glycols, saponins of quillaia extract etc.

2. Flocculating agents: On standing for a long period the suspension may become difficult to redisperse on shaking. That time, controlled flocculation is required to prevent compact sediment, which is difficult to redisperse. Controlled flocculation can be produced either by,
(i) electrolytes (e.g. potassium citrate, phosphate salts), (ii) surfactants, and (iii) polymers.

3. Suspending agents / Thickening agents: Suspending agents are the substances, which are added to a suspension to increase the viscosity of the continuous phase so that the particles remain suspended for a sufficiently long time and it becomes easy to measure an accurate dose.

                                Due to increase in viscosity of the vehicle, the particles sediment at a much slower rate.

                                e.g. methylcellulose, hydroxy propyl methyl cellulose, sodium carboxymethylcellulose, bentonite, veegum etc.

4. Preservative: The aqueous vehicle may be liable for bacterial growth, so a preservative should be used. e.g. benzoic acid, sodium benzoate, methylparaben, proptlparaben etc. may be used.

5. Organoleptic additives: Colors, sweeteners and flavoring agents may be used to make the oral suspensions more palatable.

                                      Colors:             e.g. Amaranth, Tartrazine, Caramel, and other approved colors

                                      Sweeteners:     e.g. Sucrose

                                      Flavors:           e.g. Peppermint oil, Chocolate flavor, Raspberry syrup etc.

Additives used in emulsion dosage forms

A. Emulsifying agent: The emulsifying agents stabilize an emulsion by various mechanisms. They are also known as emulgents or emulsifiers.

Classification of emulsifiers:

Type	Examples	Mode of action
Hydrophilic colloids	Vegetable source Gum acacia Tragacanth Starch Animal source Wool fat Egg yolk Gelatin Synthetic Methyl cellulose, Hydroxyethyl cellulose,	(i)       They do not reduce the surface tension but forms a rigid film on the oil droplets and form a stable o/w emulsion - thus inhibits coalescence of droplets. (ii)     As an auxiliary emulsifier they increase the viscosity of the continuous phase so that movement of dispersed phase is reduced.
Finely divided solid particles	Colloidal clays: bentonite (aluminium silicate) veegum (magnesium aluminium silicate).	(i)       They tend to absorb at the oil-water-interface and form thick impenetrable films. (ii)     Sometimes increases the viscosity of water (as continuous phase).
Synthetic Surface Active Agents	Anionic Potassium stearate Sodium lauryl sulphate Cationic Cetyl trimethyl ammonium bromide (or cetrimide) Ampholytic N-dodecyl alanine Non-ionic Sorbitan mono-oleate (TWEEN) Polyoxyethylene sorbitan mono-oleate (Polysorbate)	(i)       They form a flexible film on the oil-water interface. (ii)     They lower interfacial tension markedly and this contribute to the stability of emulsion. (iii)    In case of ionic surfactants surface charge is developed, increasing the zeta-potential, which will cause repulsion between two adjacent globules.

Difference between emulsion and suspension

Emulsions	Suspensions
1.       They contain two immiscible liquids, one of which is dispensed as minute globules into the other. 2.       Emulsifying agents are required to make a stable emulsion. 3.       Emulsions are mainly of two types: o/w and w/o. 4.       During storage, freezing should be avoided as it may lead to cracking of emulsion.	1.       They contain finely divided solid particles dispersed in a liquid or semisolid vehicle. 2.       Suspending agents are required to make a stable suspension. 3.       Suspensions are mainly of two types: (i) Flocculated and (ii) De-flocculated. 4.       During storage, freezing should be avoided as it may lead to aggregation of suspended particles.