Medicinal Emulsions Notes

Learning Outcomes

  • Definition of Emulsion:

    • An emulsion is a liquid formulation for internal application, composed of two phases:
    • Disperse phase (fine droplets of oil or water)
    • Continuous phase (water or oil)
    • Types:
    • Crude emulsion
    • Microemulsion

  • Routes of Delivery:

    • Recognize the various routes medicinal emulsions are used (oral, IV, topical).

  • Hydrophile-Lipophile Balance (RHLB):

    • Understand oily/fatty components and how to calculate the RHLB.
    • Use RHLB to select appropriate emulsifying agents.

  • Ideal Properties of Emulsions:

    • List properties and understand factors that affect stability.

  • Viscosity Modifiers and Preservatives:

    • Explain the role of viscosity modifiers and suitable preservatives in emulsion design.
What is an Emulsion?
  • Liquid Formulations:
    • For internal application (oral) vs. external (lotions/creams).
    • Composed of oil/water droplets ranging from 0.1 to 100 micrometers.
  • Types:
    • O/W (Oil in Water): Primarily for oral emulsions.
    • W/O (Water in Oil): Mainly for topical applications.
    • Multiple Emulsions: Used for specialized delivery systems.
Emulsion Types

  • Oil in Water (O/W):

    • Oil is the disperse phase and water is the continuous phase.
    • Common for oral and IV medicines.

  • Water in Oil (W/O):

    • Water is the disperse phase and oil is the continuous phase.

  • Multiple Emulsions:

    • O/W/O or W/O/W.
    • Superlative for delayed action delivery systems.
Microemulsions
  • Defined by droplet sizes of 1 nm to 1 mm, forming homogeneous, transparent systems.
  • Thermodynamically stable with more than one surfactant.
  • Commonly used for topical and IV delivery systems.
Interfacial Tension
  • Describes the energy at the interface between two phases.
  • High interfacial tension leads to coalescence of droplets.
  • Cohesive forces are stronger than adhesive forces at the interface.
Stabilisation of Emulsions
  • Emulsions initially form droplets but require stabilization to prevent separation.
  • High interfacial tension encourages droplet coalescence, leading to phase separation over time.
Choice of Emulsion Routes

  • Oral Emulsion:

    • Typically O/W, using non-toxic emulsifiers.
    • Employed for delivering oil-soluble drugs effectively.

  • Intravenous (IV) Emulsion:

    • Generally O/W, offers nutrition to patients unable to take oral feeds.
    • Uses high-caloric oils (cottonseed, olive) in formulations.

  • Topical Emulsion:

    • O/W creams for skin application; W/O creams for occlusive action.
    • Commonly use soft paraffins as bases.
Hydrophilic-Lipophilic Balance (HLB)
  • HLB Scale:
    • Measures polarity of emulsifying agents (ranges from low lipophilicity to high hydrophilicity).
    • Spans are low HLB; Tweens are high HLB.
Required HLB (RHLB)
  • Calculate the overall RHLB based on weight fractions of oil components.
  • Select emulsifying agents with appropriate HLB values for mixtures.
Ideal Emulsion and Emulsifying Agent Properties

  • Ideal Emulsion:

    • Stable globules, evenly distributed with no creaming or phase separation.
    • Should monitor bacterial growth.

  • Ideal Emulsifying Agent:

    • Non-toxic, stable at low temperatures, colorless, tasteless, and odourless.
Emulsion Stability Evaluation
  • Use macroscopic and microscopic examination for stability.
  • Assess globule size and storage conditions impacting stability.
Viscosity of Emulsions
  • Viscosity determination varies by composition; most exhibit non-Newtonian flow behavior.
  • Factors affecting viscosity include phase ratios and component interactions.
Preservation of Emulsions

  • Microbial Growth:

    • Water supports growth; emulsions must be preserved against microbes to ensure safety and efficacy.

  • Preservatives:

    • Must be effective, non-toxic, and retain activity in the emulsion matrix.
    • Examples include benzoic acid, phenoxyethanol, and quaternary ammonium compounds.
Properties of Effective Preservatives
  • Must demonstrate low toxicity, wide antibacterial spectrum, and not bind to other components.
  • Must be suitable for effective partitioning in emulsion applications.