Emulsions Flashcards
Emulsions
Dispersion in which one phase is composed of small globules of liquid is distributed through vehicle in which it is immiscible.
Parts of Emulsions
- Internal phase = dispersed phase
- External phase = dispersed medium
- Emulsifying agent = can be used to prepare stable emulsions
Emulsion Viscosity
- Can greatly vary
- Can be liquid or semisolid
- Many drugs not categorized as emulsions since they fit better in other categories
Emulsion Types (2)
- Oil-in-water (O/W) - Oleaginous internal phase and aqueous external phase. May be diluted with water
- Water-in-oil (W/O) - Aqueous internal phase and oleaginous external phase. May be diluted with oil-miscible liquid
Role of Emulsions
- Lets pharmacists prepare a stable, homogeneous mixture of two immiscible liquids
- Can disperse liquids as globules rather than in bulk
- Increases palatability
- Increases absorption of active ingredient
- Active ingredient will be less irritating on skin
Mechanism of Emulsifiers
- Interfacial tension resists large globules of liquids from breaking into smaller particles
- Emulsifying agents facilitate break up of large globules into smaller ones that have a lower tendency to coalesce
- Monomolecular layers of emulsifying agent surround the internal phase
- Emulsifying agents have both hydrophilic and lipophilic molecular regions
HLB System
- Hydrophil-Lipophil Balance
- Categorizes emulsifying agents based on chemical makeup
- Assigned numbers based on polarity
HLB + Emulsifying Agents
1-3 = Antifoaming 3-6 = W/O Emulsifying Agents 7-9 = Wetting Agents 8-18 = O/W Emulsifying Agents 13-15 = Detergents 15-16 = Solubilizers
Emulsification Preparation Methods (3)
- Continental or Dry Gum Method
- English or Wet Gum Method
- Bottle or Forbes Bottle Method
Continental Preparation Method
Primary Emulsion: 4:2:1 ratio (oil:water:emulsifier (gum))
- Gum titrated with oil in rough mortar to reduce size.
- Add water all at once and titrate immediately, rapidly, and continuously for at least 3 minutes (creamy, white emulsion with cracking sound).
- Other liquid substance with external phases are then added to primary emulsion (solid can be dissolved in a little water and be added in as well).
- Emulsions transferred to graduate and made to volume with water.
English Preparation Method
- Same ratio as continental
1. Gum is titrated with water, then oil is added slowly in portions and titrated to emulsify oil.
2. After all oil is added and mixed well, other materials (liquids and solids) are added.
3. Emulsion is transferred to graduate and brought to volume with water.
Bottle Preparation Method
Used for emulsions made from volatile oil or low viscosity oils
- One part gum and 2 parts oil are added to a bottle and shook.
- Volume of water equal to oil is added and shaken.
- Primary emulsion is then diluted with proper water volume.
Emulsion Instability
- Internal phase forms aggregated of globules when standing
- Large globules or aggregates of globules rise to top and fall to bottom and form a concentrated layer
Emulsion Creaming
- Aggregates of globules at top or bottom
- Reversible if redistributed with shaking
- If non-reversible, improper dose can result and this is NOT acceptable to pharmacist or patient
- Can increase risk of coalescence of globules
Upward Creaming
Internal phase has lower density than external phase (mostly occurs with O/W emulsions).
Downward Creaming
Internal phase has higher density than external phase (mostly W/O emulsions).
Breaking or Cracking
Coalescence of globules of internal phase and separation into a layer. IRREVERSIBLE. Layer of emulsifying agent surrounding internal phase is destroyed.
Factors Encouraging Instability of Emulsions (3)
- Increased particle size of internal phase
- Large difference in viscosities of internal and external phase.
- Decreased viscosity of external phase
Protecting Against Instability (4)
- Protect against heat and cold (at 5, 40 , and 50 degrees Celsius)
- Protect against light (light resistant container)
- Protect against air (antioxidants and tightly closed containers)
- Protect against microorganisms (bacteria, fungi, and mold can eat emulsifying agent)
Types of Emulsifying Agents (5)
- Carbohydrates (O/W) - acacia, agar, microcellulose
- Protein (O/W) - gelatin, egg yolk, casein
- High MW Alcohols (O/W) - steracyl/cetyl alcohol
- Wetting Agents (O/W or W/O) - anionic, cationic, nonionic
- Finely Divided Solids (O/W or W/O) - magnesium hydroxide, aluminum hydroxide
Emulsifying Agent Properties
1.Compatible with other ingredients in the formulation 2. Should not interfere with stability or efficacy of
therapeutic agent
3. Should be stable and not deteriorate in the preparation
4. Non-toxic with intended use and amount ingested
5. Have little color, odor or taste
6. Should have the ability to promote emulsification and
maintain stability for intended shelf-life of product
Emulsion Advantages
- Unpalatable oil-soluble drugs can be administered in palatable form
- Aqueous phase easily flavored
- Oily sensation easily removed
- Increased rate of absorption
- Possible to include two incompatible ingredients, one in each phase of emulsion
Emulsion Disadvantages
- Preparation needs to be shaken before use
- Measuring device needed for administration
- Storage conditions may affect stability
- Prone to microbial contamination
Types of Oral Emulsions (3)
- Mineral Oil Emulsions - used as lubricating cathartic, much more palatable, normal dose is 15 mL
- Castor Oil Emulsions - laxative
- Simethicone Emulsion - used as defoaming agent for gas relief in GI, changes surface tension of bubbles resulting in coalescence of free gas which is easy to eliminate, dispensed in infant drops and antacid products
