Dispersions

What is a solution?

A molecular dispersion where particles are fully dissolved in solvent, particle size < 1 nm

What are the components of a solution?

Solvent (major part) + solute (minor part)

List advantages of solutions.

Easy to swallow, fast absorption, good for feeding tubes, less bioavailability problems

List disadvantages of solutions.

Unstable, need preservatives, dosing accuracy issues, bulky, costly, solubility limits

Max residue allowed in Purified Water, USP?

≤ 0.001%

What processes are used to purify Purified Water, USP?

Distillation, ion exchange, reverse osmosis

What types of purified water are used for parenterals?

Water for Injection, Bacteriostatic Water, Sterile Water

Alcohol USP concentration?

94.9-96% at 15.56°C

At what concentration is alcohol antimicrobial?

> 12%

OTC alcohol limits by age?

6 yrs: 0.5%; 6-12 yrs: 5%; >12 yrs/adults: 10%

What is Diluted Alcohol NF?

50/50 water/alcohol mix; 3% shrinkage in volume

What is Rubbing Alcohol?

70% ethanol or IPA; external use only; germicide, skin cleanser.

Key properties of Glycerin USP?

Sweet, viscous, miscible with water/alcohol

Name common preservatives.

Parabens (methyl-, propyl-), alcohol, propylene glycol, glycerin

Name common sweeteners.

Sucrose, liquid glucose, saccharin, aspartame, sorbitol, sucralose, mannitol, polyols

Name common thickeners / viscosity enhancers.

Cellulose derivatives: methylcellulose, sodium CMC, HPMC, carbomers, povidone

Examples of aqueous solutions?

Rehydration (Pedialyte), colonic lavage (Golytely), mouthwashes (Listerine), syrups (85% sugar)

Examples of non-aqueous solutions?

Elixirs (Digoxin Elixir), tinctures (Iodine), liniments (White cream liniment), collodions, aromatic waters, spirits

What is an emulsion?

Liquid droplets dispersed in another immiscible liquid, stabilized by emulsifiers

What are the main types of emulsions?

oil-in-water (o/w), water-in-oil (w/o), oil-in-water-in-oil (o/w/o), and water-in-oil-in-water (w/o/w)

How can you identify emulsion types?

dilution test, conductivity test, and dye solubility test

What is the dilution test?

if dilution with WATER remains stable it is an o/w emulsion, and if dilution with OIL remains stable it is a w/o emulsion

What is the conductivity test?

o/w emulsions conduct electricity because water is the external phase, while w/o emulsions do not conduct

What is the dye solubility test?

water-soluble dye colors the continuous phase in o/w emulsions, while oil-soluble dye colors the continuous phase in w/o emulsions

What are the characteristics of o/w emulsions?

Water is the external phase, non-greasy, water-washable, good for oral use

What are the characteristics of w/o emulsions?

Oil is the external phase, greasy, not water-washable, good for external use

What is an emulsifying agent?

Surfactants that stabilize emulsions by reducing interfacial tension

What are examples of natural emulsifying agents?

acacia, gelatin, egg yolk, agar, pectin, and starch

What are examples of semi-synthetic emulsifying agents?

sodium carboxymethylcellulose (Na-CMC), hydroxypropylcellulose (HPC), and methylcellulose (MC)

What are examples of finely divided solid emulsifying agents?

bentonite and magnesium hydroxide

What are auxiliary emulsifiers?

stearic acid, stearyl alcohol, cetyl alcohol, glyceryl monostearate, and cholesterol

What does HLB stand for?

Hydrophilic-Lipophilic Balance, higher HLB = more hydrophilic

What is the dry gum (Continental) method?

oil is triturated first with the emulsifier, and then water is added all at once while stirring to form the primary emulsion

What is the wet gum (English) method?

the emulsifier is mixed with water first to form mucilage, and then oil is slowly added with constant trituration

What is the bottle (Forbes) method?

performed in a bottle, suitable for volatile or non-viscous oils, and uses dry or wet gum methods to form the emulsion

What is the in-situ soap method?

lime water reacts with fatty acids like oleic acid from olive oil to form calcium oleate, which acts as the emulsifier

What is the formula for a primary emulsion with fixed oil?

oil:water:emulsifier in a ratio of 4:2:1

What is aggregation (flocculation) in emulsions?

when internal phase globules loosely clump together, which is reversible upon shaking

What is coalescence in emulsions?

the irreversible merging of globules into larger ones, leading to phase separation

What is creaming in emulsions?

the reversible rising or settling of internal phase due to density differences, which may affect dose uniformity

What is cracking in emulsions?

complete separation of phases, which is irreversible and cannot be restored by shaking

What is phase inversion in emulsions?

the switching of internal and external phases, which can be reversible or irreversible depending on the cause

What are colloids and suspensions?

Heterogeneous systems with 2 phases: dispersed/internal phase & dispersing/external phase

Particle size range for colloids?

1 nm to 0.5 µm

Particle size for suspensions?

> 0.5 µm

Advantages of colloids and suspensions?

Smaller volume than solutions, better stability, taste masking, easier swallowing, flexible dosing, depot effect

Disadvantages of colloids and suspensions?

Dose inconsistency, sedimentation, caking, storage loss, and more complex manufacturing

What is flocculation?

Particles form loose clusters, settle faster, easy to redisperse

What is deflocculation?

Particles stay separate, settle slowly, form hard cake that’s hard to redisperse

What is controlled flocculation?

Stabilizes particles to prevent hard caking while allowing redispersion

How do electrolytes help controlled flocculation?

Reduce zeta potential and electric repulsion between particles

How do surfactants help controlled flocculation?

Form polymer bridges between particles to promote loose floc formation

How do polymers help controlled flocculation?

Form protective colloids that prevent caking

Name the 3 types of flocculating agents.

Electrolytes, surfactants, polymers

How does particle diameter affect sedimentation?

Larger particles settle faster

How does particle density affect sedimentation?

Higher density leads to faster settling

How does medium density affect sedimentation?

Higher medium density slows settling

How does viscosity affect sedimentation?

Higher viscosity slows sedimentation (inverse relationship)

What is wetting?

Vehicle completely contacts solute particles

How does contact angle relate to wetting?

Lower angle = better wetting; 0° = completely wet, 180° = non-wetting

Name common surfactants/emulsifiers

Anionic (SLS), cationic (benzalkonium), amphoteric (Span®, Tween®), nonionic (lecithin)

What factors affect physical stability of suspensions?

Temperature, particle aggregation, interaction with excipients