ceutics 2 emulsions

what makes up an emulsion

2 immiscible liquids

-internal/dispersed phase: droplets

-external/continuous phase: outer portion

types of emulsions

water-in-oil (w/o) & oil-in-water (o/w)

internal phase

dispersed phase

inner droplets

external phase

continuous phase

outer portion

droplets in emulsions are usually greater than _____ in size, giving a _________ appearance

0.1 micrometers; milky appearance

(microemulsion: 10-200nm)

o/w

oil in water emulsion

w/o

water in oil emulsion

w/o/w

water-in-oil-in-water

multiple emulsion

purpose of doing multiple emulsion (ex: w/o/w)

1. separates incompatible substances

2. adjusts drug release rates

advantages of emulsions

-more palatable (taste)

- greater chemical stability

- smaller oil globules = more digestible and increased absorption

- enhanced skin absorption

- less irritating to skin in internal phase

why are smaller oil globules in emulsions advantageous

1. more digestible

2. increases absorption

why are emulsions beneficials for topical drugs

1. enhanced skin absorption

2. drugs that irritate the skin are less irritating in the internal phase

castor oil

emulsion laxative

simethicone

emulsion defoaming agent

surface active agents are also known as

surfactants, amphiphiles, emulsifying agents, SAAa

amphiphilic

molecules possessing both hydrophobic (nonpolar) and a hydrophilic (polar) parts

all SAAs are amphiphilic

adsorbed

held on the surface

what allows SAAs to be adsorbed on interfaces

amphiphilic nature allows polar heads to face water and nonpolar tails to face water

where do heads and tails of surfactants face

head= polar= water

tail= nonpolar= oil

_______ must be nontoxic, stable, and compatible with water, oil, and drug

SAAs

SAAs provide droplets with ____________________ to make mutual repulsions

adequate electric potential

SAAa must be effective in __________ concentrations

low

Critical Micelle Concentration (CMC)

The surfactant concentration at which micelles form

HLB

hydrophillic/lipophilic balance (0-20), low HLB is more oil, high HLB is more water

HLB increases as

polarity/ hydrophilicity increases

HLB>9

vs

HLB

greater than 9: o/w (think hit hard, up= ow)

less than 9: w/o

mineral oil HLB in o/w vs w/o

4 in w/o

10.5 in o/w

how do you determine what HLB an emulsifier should have

should be similar to oils

overall HLB value=

sum of (each fraction * HLB)

increasing the concentration of the internal phase to >75% can cause

inversion

why does inversion lead to instability

if SAA favors o/w and it is inverted to w/o, then it is no longer stable

4 classifications of SAA based on ionic contents

1. anionic= negative charge on head

ex: sodium layryl sulfate in toothpaste, tri ethanolamine dodecyl sulfate, sodium dodecyl benzene sulfonate

(SLS, TEDS, SDBS)

2. cationic= positive charge on head

= bacteriostatic, reacts w cell wall

ex: quaternary ammonium, cetyl trimethyl ammounium Br

3. ampholytic= both + and - zwitterionic head, depends on pH

4. non-ionic= water soluble head that does NOT have charge

Spans (w/o) and Tweens (o/w)

which SAAs are bacteriostatic

cationic

Spans vs Tweens

both nonionic SAAs

Spans (Sorbitan fatty acid esters)= oil soluble, promote w/o

Tweens (PEG-sorbitan fatty acid ester)= water soluble, promote o/w

(think tweens= mean= ow)

3 theories of emulsification (summary)

1. surface tension theory

= liquids assume shape with least amount of area exposed

=SAA lowers interfacial tension= break globules into smaller parts= reduce coalescence

2. oriented-wedge theory

= formation of MONOmolecular layer around drops = prevent coalescence via 1) electrical repulsion 2) physical separation via layer

3. interfacial-film theory

= MULTImolecular film at interface prevents coalescence

1) increases viscosity 2) charge repulsion

interfacial tension

Interphase between two liquids

SAA vs interfacial tension and coalescence

SAAs LOWER interfacial tension and REDUCE coalescence

high pressure homogenizer

uses high pressure to make homogenized product

continental/ dry gum method

1. add gum/SAA to oil

2. add water all at once and triturate= crackle and white

3. add other ingredients

fixed(4o:2w:1g)

mineral (3o:2w:1g)

volatile (2o:2w:1g)

English/wet gum method

(think england= wet)

1. add gum/SAA to water

2. add oil slowly and triturate

3. add other ingredients

Bottle Method

*used for volatile oils or low viscosities

1. gum and oil shaken in bottle

2. add water and then oil in proportions

micro/nano emulsions

clear

transparent

thermodynamically stable systems of two immiscible fluids

size of micro/nano emulsions

10-200nm

why arent nanoemulsions not true solutions

they are dispersions of oil, so even though they are transparent, they arent completely soluble like a solution

example of SAA used in micro/nano emulsions

polysorbate 60 and 80

micro/nano emulsion advantages

- rapid oral absorption

-increased diffusion into skin

-targets cytotoxic drugs to cancer cells

how can you dilute emulsions

o/w: dilute with water (external phase)

w/o: dilute with oil

what emulsions can conduct an electric current

o/w (water is conductor)

which emulsions can be colored by water soluble dyes

o/w

Creaming of emulsions

internal phase droplets separate slightly (oil to top, water to bottom)

= reversible

= may lead to improper dosing

Cracking/breaking of emulsions

internal phase globules seperate into a PERMANENT LAYER that CANNOT be fixed

how can you stabilize emulsions/ reduce coalescence

1. reduce particle size

2. minimal density difference between internal and external phase

3. high viscosity of external phase

4. proper SAA selected

coalescence

The process by which parts of a whole join together, or fuse, to make one

emulsion inversion

changing of an emulsion from o/w to w/o

what environmental conditions can affect the stability of an emulsion

temp, light, air

what can be added to reduce oxidative decomposition

antioxidants

what can be added to reduce contamination from microbes

methylparaben, propylparaben, alcohol