emulsion dosage forms Flashcards
What are some pharaceutical applications of emulsions?
- Topical delivery (creams)
- Total parenteral nutrition (intravenous feeding of fat emulsions)
- Oral delivery and taste masking (cod liver oil)
- As vehicle for drug (emulsions containing propofol)
What is an emulsion?
A ‘pseudo-stable’ dispersion of at least two immiscible liquids, one of
which is dispersed throughout the other in the form of fine droplets
(generally oil and water) stabilised by the presence of an emulsifying
agent (known as emulsifier)
What are some characteristics of emulsions?
- Cloudy or milky
- Droplet sizes are polydispersed (nm to μm)
- Low concentration of surfactant/cosurfactant
- Thermodynamically unstable but kinetically stable
(feasible to separate, but happens very slowly) - Prepared by input of large amount of energy, e.g. high speed
homogenisation, sonication, heat
What are the emulsion types?
- Normal emulsion (o/w)
- Reverse emulsion (w/o)
- Multiple emulsion
(o/w/o or w/o/w)
What are some examples of w/o emulsions?
- w/o emulsions
- Sunscreen
- w/o/w emulsions
- Vancomycin hydrochloride – enhanced enteral bioavailability
What is an example of a o/w emulsion?
- Vehicles for lipophilic drugs
What are creams made up of in terms of emulsions?
Semi-solid emulsions of two immiscible phases stabilised by emulsifying
agent (either o/w or w/o)
What are some characteristics and properties of ‘watery’ (o/w) creams?
- Water is the continuous medium, while oil is the dispersed
phase, therefore o/w creams do not feel greasy - Can deposit lipids so restore skin hydration, however they
are non-occlusive - Rub into the skin, leaving behind a thin film of rapidly
releasing water-soluble drug - Readily diluted and miscible with water; easily rinsed off
- Conduct electricity
- Prepared using surfactants with higher HLB (8-16)
What are some characteristics and properties of ‘oily’ w/o creams?
- Are more greasy, since oil is the continuous phase
- More moisturising as they provide an oily barrier which
reduces water loss from the outer layer of the skin - Hydrophobic drugs are better formulated and more
readily released - Miscible with oil therefore not easily washable, however
more easily spreadable - Do not conduct electricity
- Prepared using low HLB surfactants (3.5-8)
What do semi-solid creams require?
Semi-solid creams require excess surfactant/co-surfactant compared to
that required for stabilising runny emulsions
* The excess surfactants form structures in the bulk phase producing complex
semi-solid multiphase systems
What are the four phases observed in an o/w cream prepared by cetostearatyl alcohol?
- Dispersed oil phase
- Bulk water phase
- Crystalline gel phase
containing interlamellar fixed
water - Phase composed of crystalline
hydrates of cetostearyl alcohol
What are the benefits to a greasier emollient? +downside
Generally, the greasier an emollient, the more effective it is, as it is able to
trap more moisture in the skin
* However greasy emollients are often less acceptable or tolerated
Why are creams better than ointments?
Creams are less greasy but generally more acceptable than ointments
Why are lotions better than creams and ointments?
Lotions are good for very mild dry skin and for the face. They can also be
used in hairy places where the application of ointments or thicker creams can
be quite messy
Why are ointments okay?
Ointments should not be used where an infection is present (unless it is an
antibiotic ointment)
* Over-use of greasy ointments can lead to folliculitis (blockage and inflammation of
hair follicles)
