PHA 338 - Colloids, Emulsion and Suspension L10
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136 Terms
What is a pharmaceutical disperse system?
A heterogeneous (two-phase) system containing undissolved or immiscible material distributed throughout a vehicle.
What are the major types of two-phase liquid dosage forms?
Suspensions, emulsions, gels, and magmas.
What is a colloid?
A homogeneous or heterogeneous mixture with particles intermediate in size between solutions and suspensions that do not settle upon standing.
What is a suspension?
A heterogeneous mixture with relatively large particles that settle upon standing.
What determines whether a system is a solution, colloid, or suspension?
Particle size.
Arrange solution, colloid, and suspension from smallest to largest particle size.
Solution → Colloid → Suspension.
Do colloidal particles settle out upon standing?
No.
Do suspension particles settle out upon standing?
Yes.
What is a gel?
A colloidal mixture of a solid dispersed in a liquid.
What is a sol?
A colloidal mixture of a solid dispersed in a liquid.
What is an emulsion?
A colloidal mixture of a liquid dispersed in another liquid.
What is an aerosol?
A colloidal mixture of a liquid dispersed in a gas.
What is a foam?
A colloidal mixture of a gas dispersed in a liquid.
What are the three major problems associated with two-phase systems?
Wetting, particle aggregation, and interfacial tension.
What is wetting?
The displacement of air from a solid surface by a liquid and spreading of the liquid over the solid.
What indicates the degree of wetting?
Contact angle.
What contact angle indicates complete wetting?
0°.
What contact angle indicates no wetting?
180°.
What happens if a drug powder is not wetted?
It will float and may not dissolve or be absorbed.
What is a wetting agent?
A substance that improves the ability of a liquid to spread over a solid surface.
What surfactant is commonly used as a wetting agent?
Sodium lauryl sulfate.
How do bile acids affect wetting?
They act as natural surfactants and improve wetting.
What is particle aggregation?
Clumping of particles together.
Why is particle aggregation undesirable in suspensions?
It can form hard cakes that are difficult to redisperse.
What is flocculation?
Formation of loose particle aggregates that settle rapidly but are easily redispersed.
What is a flocculating agent?
A substance that promotes controlled flocculation.
What types of substances can act as flocculating agents?
Electrolytes, charged surfactants, and charged polymers.
How can particle aggregation be prevented?
By giving particles similar charges so they repel each other.
How does ion valence affect flocculation?
Flocculation increases with increasing ion valence.
What is interfacial phenomenon?
The study of properties of molecules located at the boundary between immiscible phases.
What is interfacial tension?
The force existing at the interface between two immiscible phases due to differences in molecular interactions.
What is surface tension?
The elastic-like force existing at the surface of a liquid.
How does temperature affect surface tension?
Surface tension decreases as temperature increases.
How does temperature affect interfacial tension?
Interfacial tension decreases as temperature increases.
What is an emulsion?
A dispersion of small liquid globules distributed throughout another immiscible liquid.
What is the dispersed phase of an emulsion called?
The internal phase.
What is the dispersion medium called?
The external or continuous phase.
Are emulsions thermodynamically stable?
No, they are metastable.
Why is an emulsifying agent needed?
To stabilize the emulsion and reduce interfacial tension.
What are common routes of administration for emulsions?
Oral, topical, and parenteral.
What is an oil-in-water (o/w) emulsion?
Oil is the internal phase and water is the external phase.
What is a water-in-oil (w/o) emulsion?
Water is the internal phase and oil is the external phase.
What type of emulsion is milk?
Oil-in-water (o/w).
What type of emulsion is butter?
Water-in-oil (w/o).
What are the three classes of emulsifying agents?
Surface acting agents (surfactants), hydrophilic colloids, and finely divided solid particles.
How do surfactants act as emulsifying agents?
They adsorb at interfaces and reduce interfacial tension.
What characteristics must surfactants possess?
Both hydrophilic and hydrophobic portions.
What are hydrophilic colloids?
Water-soluble polymers that form a multimolecular film around dispersed droplets.
How do hydrophilic colloids stabilize emulsions?
By forming a protective film and increasing viscosity.
Give examples of hydrophilic colloids.
Acacia, tragacanth, agar, pectin, gelatin, and casein.
What are finely divided solid particles as emulsifying agents?
Solids adsorbed at the interface that form a protective film around droplets.
Give examples of finely divided solid particle emulsifiers.
Bentonite, magnesium hydroxide, and aluminum hydroxide.
What is adsorption?
Binding or accumulation of molecules on a surface.
What is absorption?
Filling of pores within a solid.
What are the four methods of emulsion preparation?
Dry gum, wet gum, bottle (Forbes), and beaker methods.
What is another name for the dry gum method?
Continental method.
What is the dry gum ratio?
4:2:1 (oil:water:gum).
In the dry gum method, what is mixed first?
Oil and gum.
What indicates successful primary emulsion formation in the dry gum method?
A snapping sound.
What is another name for the wet gum method?
English method.
In the wet gum method, what is mixed first?
Water and gum to form mucilage.
What method is used for volatile oils and low-viscosity oils?
Bottle (Forbes) method.
What occurs during emulsion breaking?
Irreversible separation of the internal and external phases.
What is coalescence?
Complete fusion of droplets leading to phase separation.
What is creaming?
Accumulation of droplets at the upper portion of an emulsion.
How can coalescence be reduced?
By adding an emulsifying agent.
Why are preservatives added to emulsions?
To prevent microbial contamination.
Give examples of preservatives used in emulsions.
Methylparaben, propylparaben, and alcohol.
What is a microemulsion?
A clear, transparent, thermodynamically stable system containing swollen micelles.
How is a microemulsion different from a regular emulsion?
It is thermodynamically stable and transparent.
What four components make up a microemulsion?
Aqueous phase, oily phase, surfactant, and emulsifying agent.
What is the typical droplet size range of a microemulsion?
10–100 millimicrons.
What are common applications of microemulsions?
Oral and topical drug delivery.
What advantage do microemulsions provide in topical delivery?
Enhanced transdermal drug absorption.
What is Neoral?
A cyclosporine oral microemulsion.
What is Topicaine?
A lidocaine gel microemulsion.
What does SURFACTANT stand for?
SURFace ACTive AgeNT.
What is a surfactant?
A molecule containing both hydrophilic and lipophilic regions that acts at interfaces.
What structures do surfactants commonly form?
Micelles.
What are the five classes of surfactants?
Anionic, cationic, amphoteric, nonionic, and naturally occurring.
Which surfactant class is most commonly used?
Anionic surfactants.
Give examples of anionic surfactants.
Sodium lauryl sulfate and potassium laurate.
What charge do cationic surfactants possess?
Positive charge.
Give examples of cationic surfactants.
Benzalkonium chloride and dodecylamine HCl.
What is a major pharmaceutical use of cationic surfactants?
Antimicrobial preservatives.
What are amphoteric surfactants?
Surfactants that can behave as anionic, cationic, or nonionic depending on pH.
What are nonionic surfactants?
Surfactants that contain no ionic groups.
Give examples of nonionic surfactants.
Tweens, Spans, Brijs, and Cremophor.
What are naturally occurring surfactants?
Phospholipids and bile salts.
What is the function of bile salts?
Emulsify fats and improve absorption of poorly soluble drugs.
What is sodium lauryl sulfate used for pharmaceutically?
Wetting agent, solubilizer, and shampoo ingredient.
What is benzalkonium chloride used for pharmaceutically?
Preservative, disinfectant, antifungal agent, and skin cleanser.
What is HLB?
Hydrophilic-Lipophilic Balance.
What does the HLB value indicate?
The balance between hydrophilic and lipophilic portions of a surfactant.
What HLB range corresponds to antifoaming agents?
0–3.
What HLB range corresponds to water-in-oil emulsifiers?
4–6.
What HLB range corresponds to wetting agents?
7–9.
What HLB range corresponds to oil-in-water emulsifiers?
8–18.
What HLB range corresponds to detergents?
13–16.
What HLB range corresponds to solubilizers?
15–20.