Emulsions and Creams

🧪 What is an Emulsion?

• An emulsion is a dispersion of two immiscible or partially miscible liquids.

• One liquid is dispersed as fine droplets (dispersed phase) throughout the other liquid (continuous phase).

💧 Types of Emulsions

1. Oil-in-Water (O/W)

• Oil droplets dispersed in water

• Common in oral, IV, and topical use

• Polymer solutions may form O/W emulsions

2. Water-in-Oil (W/O)

• Water droplets dispersed in oil

• Used in topical, SC, and IM delivery

3. Multiple Emulsions

• Oil-in-Water-in-Oil (O/W/O): O/W emulsion further dispersed in oil

• Water-in-Oil-in-Water (W/O/W): W/O emulsion further emulsified in water

• Used in controlled release and vaccine delivery

📊 Classification of Emulsions

Droplet Size Types

🔬 O/W vs W/O Emulsions

💊 Emulsions vs Suspensions

🚀 Applications in Drug Delivery

• Enhance absorption of poorly soluble drugs & vitamins

• Mask taste of unpleasant oil-soluble drugs

• IV O/W emulsions: e.g. Intralipid® for TPN, drug carriers

• Contrast agents: Iodised oils, bromised oils for imaging

• W/O emulsions: SC or IM, e.g. for vaccines (longer immunity)

• Topical creams: O/W or W/O based on skin needs

📦 Routes of Delivery

✅ Advantages of Emulsions

• Deliver lipophilic drugs effectively

• Allow parenteral nutrition

• Better absorption vs suspensions/tablets

• Taste masking

• Topical: soothing and cleansing

❌ Disadvantages of Emulsions

• Thermodynamically unstable

• Require emulsifying agents

• Susceptible to coalescence, creaming, phase inversion

• May need special packaging/storage

🧱 Pharmaceutical Emulsion Types

⚗ Emulsion Components

1. Oil Phase

• May carry the drug

• Oral: Castor oil, liquid paraffin

• Topical: Hydrocarbons (e.g. mineral oil)

• Parenteral: O/W for IV only; purified mineral oil for IM

2. Emulsifying Agents

• Reduce interfacial tension & prevent coalescence

Types:

• Surfactants: e.g. Sodium stearate, SDS

  • Hydrophilic + hydrophobic ends

  • Adsorb at interface, form monolayer

  • Provide charge & steric stabilisation

• Hydrophilic colloids: e.g. Gum arabic, pectin

  • Form multimolecular film

• Finely divided solids: e.g. Bentonite

  • Form particulate film

3. Additives

🧪 Emulsion Formation

1. Two immiscible liquids: High surface tension & polarity difference

2. Agitation: Increases surface area, forming droplets

3. Free Energy Increase: ΔG = γ × ΔA

   • (γ = surface tension, A = surface area)

4. Thermodynamically Unstable: Droplets tend to coalesce

5. Emulsifiers: Reduce interfacial tension and stabilise droplets

⚙ Emulsification Process

Two Simultaneous Processes:

• (1) Droplet Formation (Energy input):
  → Requires agitation to disperse droplets and increase energy

• (2) Coalescence (Spontaneous):
  → Droplets merge to reduce free energy
  → Ceases only if system fully separates

⚠ Emulsion Instability Issues

🧪 Emulsion Type Testing

🧴 Creams: Special Emulsion Form

• Semi-solid emulsions used on skin/mucous membranes

• Can be O/W (washable) or W/O (greasy, more emollient)

• Offer local or systemic drug effects

Cream Formulation Components