Exam 1 Flashcards
Define emulsion, internal phase and external phase
An emulsion is defined as a dispersed system containing at least two immiscible liquids
One of the liquids (internal phase) is finely subdivided and uniformly distributed as droplets throughout the other (external phase)
Droplet size in emulsions
0.1 - 100 µm (nanometers)
In an emulsion, one liquid is ______ and one is _______
Invariably, one of the two immiscible liquids is aqueous, while the other is oleaginous
What are the two types of emulsions? Define them.
Oil-in-Water (O/W) Emulsions:
an emulsion in which the oil is dispersed as droplets throughout the aqueous phase
Water-in-Oil (W/O) Emulsions:
an emulsion in which water is the dispersed phase and an oil is the continuous phase (dispersion medium water
O/W Emulsion Water Content? What is the internal phase?
water > 45% of total weight
oil is internal phase
W/O Emulsion Water Content? What is the internal phase?
dispersion medium water < 45%of total weight
water is internal phase
What is a multiple emulsion? Why were they created?
have been developed to produce a sustained release of the active ingredient.
any drug present in the innermost phase must cross two phase boundaries to reach the external or continuous phase (to be available for absorption)
Define W/O/W
consist of small water droplets which are enclosed in a large oil droplet, which in turn is dispersed in water
Define O/W/O Emulsion
small oil droplets are enclosed in a large water droplet, which is dispersed in oil
What are some advantages of emulsions as dosage forms?
Unpalatable drugs can be administered in palatable form
Aqueous phase easily flavored
Oil sensation easily removed
Increased rate of absorption
Easy parenteral adminstrratuion where lipid componenet phase is important
Possible to include two incompatabible ingedirnts; one in each phase of the emulsion
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Why are emulsions advantageous over suspensions?
Bypasses dissolution and makes easier absorption (already in mononuclear phase)
Advantage over suspensions (suspensions in granular form)
For oral admin, emulsions are mainly….. WHy
O/W –> Ensure pleasant taste
For intravenous administration, emulsions are mainly….. Why
O/W –> Other serious embolization may occur
Intramuscular administration, emulsions are…. Why?
Usually w/o emulsions for depot therapy (sustained release)
External administrations are …….
Emulsified lotions, creams or liniments may be either o/w or w/o depending on their desired use.
What are some characteristics of topical O/W emulsions and W/O emulsions?
O/W: Not greasy, water-washable
W/O: Greasy, occlusive, form water repellent film
What emulsions are lotions, creams, and ointments?
Lotions - O/W
Creams - O/W or W/O
Ointments - W/O
What are the components of an emulsion?
Oil phase
Water Phase
Emulsifying Agent/ emulsifier –> Makes water and oil miscible and provides a homogenous agent
What oils are used for the oil phase in oral emulsions? What are they also? Iv? External?
liquid paraffin
castor oil
arachis oil (peanut oil)
cod liver oil
LAXATIVES
IV
Cottonseed
Soyabean
Safllower
Topical
Benzyl-benzoate
Turpentine
Various oils (e.g. liquid parrafin) as carriers for active ingredient
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What is a fixed-oil? Examples?
non-volatile/fatty oil of animal or plant derivation a mixture of esters of fatty acids, usually triglycerides
- Castor oil, Cod liver oil, olive oil
What is an essential or volatile oil? Example?
non fatty oils from plants
- Mint oil, rose oil, peppermint oil
What is mineral oil? Example?
- A grade of liquid petrolatum
- Liquid parrafin
What may be used for the water phase in an emulsion?
Water
Glycerol
Propylene glycol
Polyethylene glycols
Sorbitol
Emulsion equation
Emulsions = oil + water + emulsifier + energy
How do emulsifier stabilize the system in general?
All emulsifying agents concentrate at oil/water interface to provide protection by:
a) Reducing the interfacial tension
b) Imparting a charge on the droplet –> electrostatic repulsion
What are the requirements of an emulsyfying agent?
Molecular Structure
Stable Interface
Chemical Stability
Inertness
Non-toxic, non-irritating
Odorless, taseteless, colorless
Non-cost prohibitive
How are emulsifying agents classified?
a) Based on chemical structure
i) Synthetic and semi-synthetic
ii) Natural
iii) Finely dispersed solids
iv) Auxillary agents
b) Based on mechanism of action
i) Surface active agents
ii) Hydrophillic colloids
iii) Finely divided solid particles
What are the natural emulsifying agent?
Plant Derivatives (mainly water soluble natural polymers) such as tragacanth
Animal derivatives like gelatin, lanolin (w/o), cholesterol and lecithin
What are the semi-synthetic emulsyfying agents?
Cellulose derivatives (mainly water soluble polymers) like methylcellulose and carboxymethycellulose
What are the synthetic emulsyfying agent?
Polymers like PVP, PEG, or carbomer (hydrocolloid)
Surfactants
How are surfactants subdivided?
- Anionic - Negative hydrophilic head
- Soft soaps alkali metal and ammonium soaps can be formed in-situ, O/W emulsions - - Sodium triethanolamine-stearte
- Hard soaps of divalent and tri-valent metals W/O emulsions - Calcium Oleate
- Detergents sulfated and sulfonated compounds O/W emulsions - Sodium lauryl sulfate - Cationic - Positive polar head
- Quaternary ammonium compounds (Benzylklonium, benetholium chloride)
- Used as preservative sin opthalmic formulations - Non-ionic
- Most commonly contain an OH and/or ethylene oxide group
- Fatty acid or alchol (12-18 carbon chain)
–> If hydrophobic predominates, surfactant is oil soluble
–> If the hydrophilic portion predominates –> Surfactant is water soluble
- SPANS AND TWEENS
- Amphoteric
- Carry both a positive and negative charge
-Cationic Part –> primary, secondary or tertuiary amines or quaternary ammonium
- anionic part –> Variable
What are the finely divided solids emulsyfying agents?
Form a particulate layer around dispersed droplets –> swell in dispersion medium –> increases inter-particle distance –> minimize inter-particle interaction (process is what makes them have surfactant activity)
Most of them support o/w emulsions. Some like bentonite can form w/o emulsion as well
Viscosity depends on the internal concentration i.e. relative volume of the internal phase
- E.g. bentonite, Veegum
What are auxillary emulsifiers?
Weak emulsifiers therefore, always used in combination with other emulsifiers
Stabilize the system by thickening (increasing the viscosity) –> retard inter-particle movement
Examples fatty acids (stearic acid), fatty alcohols (stearyl or cetyl alcohol) or fatty esters (glyceryl mono stearate)
How can one choose an emulsifying agent?
Depends on the emulsifying ability desired and the toxicity (determines route of administration) of each emulsifying agent.
Why are non-ionic emulsifiers beneficial?
) Non-ionic Emulsifiers
- less toxic, less irritant
When can ionic emulsifiers be used?
Ionic Emulsifiers
- should not be given orally (irritant to GIT)
Cationic: toxic at low concentrations –> limited to external use when antiseptic properties are required
Anionic: have high pH (alkaline) –> unsuitable for broken skin
What emulsifiers are used for parenteral use?
Parenteral Use
- Only certain types of non-ionic surfactants may be used for parenteral administration
e.g. lecithin, polysorbate 80
In regards to the mechanism of action of an emulsifying agent, they are classified according to……
The type of interfacial film formed:
1) Mono-molecular Film
2) Multi-molecular film
3) Solid particle film
Define Mono-molecular film
Move from liquid –> liquid interface
–> higher concentration at interface compared to the bulk –> reduces the surface interfacial tension
(surface active agent)
Define Multi-molecular film
Causes NO change in interfacial tension and protects coalescence (combination) by:
- Protective sheath around the droplets
- Imparting charge to the droplets –> repel each other
- wetting to increase viscosity –> less likely to merge
(hydrocolloids)
Define solid-particle film
Forms particulate layer –> swells –> increase viscosity –> retard droplet movement
(finely divided solids)
What is the most common type of emulsifier? What is a structural feature common in all surfactants? The concepts related to the actions of these surfactants will help us decide:
Surfactants
Hydrophilic head and Hydrophobic tail
a) Amount
b) Type
Describe amphipathic properties and adsorption at interfaces
- Hydrophobic tail has affinity for oil
- Hydrophilic head has affinity for water
Amphipathic refers to a chemical entity which possesses two distinctly different characteristics, such as a molecule which has both hydrophobic and hydrophilic characteristics (also termed amphiphilic).
What occurs at the interface of two immiscible substances? What reduxes it?
When one liquid is in contact with a second liquid in which it is immiscible, the force causing each liquid to resist mixing is called interfacial tension
Surfactants lower the interfacial tension.
What do surfactants do in an aqueous medium?
Surface Adsorption
V
Monomers
V
Micelle
Describe how surfacatants form micelles?
A low concentration of surfcactant - just adsorption
Surface adsorption increases as concentration of surfactant increases. Surfactant starts to form monomers
At CMC, surfactant concnetration is enough where micelles start to form
How are micelles formed?
Micelles are formed by self-assembly of amphiphilic molecules (surfactants).
What is the CMC?
the concentration of surfactants above which micelles form and all additional surfactants added to the system will form micelles
Define aggregation number
the average number of surfactant monomers in a spherical micelle e.g. 8
In an emulsion, do we want a high CMC or a low CMC?
If CMC is low, surfactants form micelles before coating the droplets
Want a high CMC
Describe the difference between micelle characteristics with non-ionic and ionic surfactants?
Non-ionic surfactants form micelles at lower concentrations than ionic surfactants
Micelles and Monomer Surfactant Relationship
Micelles are in dynamic equilibrium with monomeric surfactant molecules in the emulsion
What CMC value of a surfactant do you want for an emulsion?
If the CMC is low –> surfactant will form micelles before oil (or water) droplets can be coated
a surfactant with a low CMC emulsification is not as efficient as one whose CMC is higher
What is a mixed micelle?
If a blend of surfactants is used in the preparation of an emulsion –> formation of mixed micelles
Describe the lipophile balance?
more hydrophilic emulsifiers,
form o/w emulsions
more lipophilic emulsifiers,
form w/o emulsions
What is the numeric system of classifying lipophile balance?
Numeric Measurement = HLB system
What is the HLB system?
Assigns each surfactant an HLB number –> its relative polarity
The HLB scale is a numerical scale ranging from 1 to approximately 50
Most surfactants fall between 1-20
Describe the solubility of SPANs and TWEENS
If the hydrophobic portion predominates –> surfactant is oil soluble = SPANS
If the hydrophilic portion predominates –> surfactant is water-soluble = Tweens
What determines a lipophilic and hydrophilic surfactant?
Low HLB numbers (0-10) –>low polarity –>
LIPOPHILLIC SURFACTANT
High HLB numbers (10-20) –> high polarity –>
HYDROPHILIC SURFACTANT
Water Soluble Surfactants and HLB agents. What type of emulsion?
8-16
Emulsifying agents for o/w emulsions
Oil Soluble Surfactants and HLB agents. What type of emulsion?
3-8
Emulsyfying agents for W/O emulsions
Surfacatants for a stable emulsion?
Combination of surfactant in specific ratios –> more stable emulsion
What are spans?
Spans are sorbitan fatty acid esters having low HLB values ranging from 1.8 to 8.6.
Spans are lipophilic
What are Tweens?
Tweens (think of W, water) are polyoxyethylene derivatives of spans.
So, they are more hydrophilic having higher HLB values ranging from 10.5 to 16.7.
What are the required HLB values for an emulsion?
Oils in the emulsions require
a specific HLB value to be formulated as o/w or w/o emulsion
For the same oil:
If w/o emulsion desired=low HLB value to impart lipophilicity (3-8)
If o/w emulsion desired=high HLB values to impart hydrophilicity (8-16)
What is used to obtain the required HLB of the oil?
Mixture of surfactants with high and low HLB values are used to obtain the required HLB of the oil