Pharmaceutics: Emulsions and Emulsifiers

Deflocculation and Stabilisation

• Deflocculation: particles separate
• Stabilisation effect: reducing interfacial tension, forming a rigid interfacial film, and formation of an electric double layer

Emulsifiers

• HLB (Hydrophilic-Lipophilic Balance) equation: measures the balance between hydrophilic and lipophilic parts of an emulsifier
• Types of emulsifiers:
  • Anionic: Na lauryl SO4, Ca Oleate, Cetostearyl alc.
  • Cationic: Cetrimide
  • Non-ionic: Tween 80, Glyc. Monostearate, Span 60, Cetomacrogol 1000

Ointment Bases

• Types of ointment bases:
  • Hydrocarbon-based
  • Oleaginous
  • Absorption bases
  • Water-soluble bases
  • Water-miscible bases
  • Removable bases

Creams

• Types of creams:
  • Aqueous creams (anionic)
  • Cetrimide creams (cationic)
  • Sorbolene and cetomacrogol creams (non-ionic)

Colloids

• Properties of colloids:
  • Lyophilic: stable, interacts well with dispersion medium, and forms with relative ease
  • Lyophobic: opposite to lyophilic, uses insoluble particles
  • Association: dispersed phase are aggregates of small molecules
• Examples of colloids:
  • Gelatin, acacia, albumin, and insulin in water (lyophilic)
  • Au, Ag, S, and AgI (lyophobic)

Colloid Preparation Methods

• Dispersion: particles ground in solvent mill, subjected to high heat, and forced through a narrow gap between 2 rotating surfaces to tear particles apart
• Chemical methods:
  • Dissolution and precipitation
  • Condensation
• Emulsion: emulsifier is added to create a homogenized solution

Imbibition and Syneresis

• Imbibition: takes up a certain liquid amount without an increase in gel volume
• Syneresis: gel contraction caused by interaction of particles of the dispersed phase

Hydrogels

• Provides absorption, desloughing, and debriding capacities to necrotic and fibrotic tissues
• Fills the wound cavity and protects granulating tissue

Suspensions

• Coarse dispersions of fine, large, and insoluble particles
• Formulated to allow for easy swallowing, dosage separation, palatability, stability, and prolonged action/relief

DLVO Theory

• Related to energy of attraction (van der Waals forces) and repulsion (electric double layer)
• The second minimum is beneficial as particles have a limited overall attraction to each other and behave as floccules (loose aggregates of individual particles)

Emulsions

• Advantages: can be administered without swallowing difficulty, disguises tastes or smells of oils or oil-based drugs, and improves absorption of poorly soluble drugs
• Disadvantages: thermodynamically unstable, difficult to formulate and manufacture

Dermatological Recommendations

• Clean treatment area, remove any matting hair, spread a thin and even layer of medication, and leave
• Do not cover unless absolutely necessary
• Remind patients of drug safety

Sterilisation Methods

• Heat: steam or dry heat
• Gas: ethylene oxide and inert gas
• Radiation: gamma or beta radiation
• Filtration: physically removed from drug

Sterility Assurance Levels (SAL)

• Probability of 1 unit being non-sterile
• Topical: 1 in 1000
• Parenterals: 1 in 10^6

Viscosity Inducing Agents

• Gelatin, Agar, alginic acid, guar gum, dextrin, and xanthan gum

Colloidal Drug Delivery Systems

• Micelles, microemulsions, liposomes, parenteral emulsions, microspheres, nanoparticles, and drug-polymer conjugates

Determining Colloidal Particle Size

• Hydrodynamic chromatography
• Light scattering
• Electron microscopy
• Tyndall effect

Liposomes

• Drug delivery vehicle with a lipid bilayer and a hydrophilic, aqueous area
• Used for enhancing drug targeting and passive or active targeting

Microspheres

• Spherical particles with a diameter in micrometres
• Porous and allows a delayed release due to its structure

Nanoparticles

• Prepared with polymers and lipids as well as proteins
• Pegylated: coated with PEG to increase solubility

Gels

• Single-phase gels: no clear boundary between particles and more restricted movement
• Two-phase gels: individual particles that are cross-linked and have limited movement
• Hydrogels: in-organic
• Organogels: hydrophobic

Effect of pH on Dispersions

• Carbopol: can form acidic solution, causing neutralisation and precipitation
• Cellulose derivatives: wide pH range
• Bentonite magma: addition of acid reduces pH, causing instability and reducing absorption of water

Desirable Properties of Suspensions

• Non-rapid settling
• Easy redispersion
• Free-flow
• Uniform dosage after shaken
• Particle size constant
• Acceptable to patient

Flocculation vs Deflocculation

• Flocculation: aggregates formed
• Can occur by reducing zeta potential
• Deflocculation: particles separate