Lecture 21: Creams Flashcards
What is a cream?
- Semi-solid emulsion
- Dispersed system stabilised using a suitable emulsifier
- Multiphase consisting of lipophilic and aqueous phase
- Soft spreadable consistency
What is the administration of creams?
- Topical (external) for application to skin or mucous membrane
What is O/W cream?
- Oil in water semi-solid emulsion
- Hydrophilic
What are the phases of hydrophilic O/W?
- Oil droplets dispersed in water (continuous)
What is W/O cream?
- Water in oil semi-solid emulsion
- Lipophilic
What are the phases of lipophilic W/O?
- Water droplets dispersed in oil (continuous)
What are the characteristics of a hydrophilic (O/W) cream?
- Non-greasy
- Miscible with skin secretions
- Water-washable (easily washed)
- Non-occlusive
What are the characteristics of a lipophilic cream (W/O)?
- Somewhat greasy (less than ointments)
- Less miscible with skin secretions than O/W
- Less water-washable than O/W
- Somewhat occlusive (less than ointments) (no evaporation)
What are the 4 basic components of a cream?
- Drug
- Continuous phase
- Dispersed phase
- Emulsifier - to stable emulsion
What is the purpose of an emulsifier in liquid emulsions?
- Allow the droplets to remain as droplets in the cream
- Required as 2 phases are immiscible
What are 6 other components a cream can contain and their purposes?
- Co-solvent: Enhances solubility
- Thickener: Enhances viscosity/stability/release profile
- Preservative: Prevents microbial spoilage (from water)
- Penetration enhancer: Enhances drug penetration (skin barrier)
- pH regulator: adjusts pH, reduces irritation
- Antioxidant: prevents oxidative degradation (it gets oxidised instead of drug)
How do you prepare a cream (5)?
- Dissolve lipophilic ingredients (molten) in oily phase at minimum temp necessary
- Dissolve hydrophilic ingredients in aqueous phase, heat to same temp as oily phase
- Mix both phases at same temp
- Stir until emulsion (cream) is formed
- Incorporate solids by trituration
To ensure sufficient dose and even dispersion of ingredients, what must be done?
- Good solubility in either phase -> can make solution into suspension and suspend solid particles in
- Or incorporate solids homogenously by trituration
How do you ensure a stable emulsion?
- Choice of suitable emulsifiers, commonly amphiphilic surfactants
- Hydrophile-lipophile balance (HLB) and Bancrofts rule
What is HLB (hydrophilic-lipophilic balance (0-20)) ?
- Is a scale that helps formulators choose the right emulsifier for creams and other emulsions.
- It indicates whether a substance is more water-loving (hydrophilic) or oil-loving (lipophilic).
- If making an O/W cream, use an emulsifier with a high HLB (e.g., 10–16).
- For a W/O cream, use an emulsifier with a low HLB (e.g., 3–6).
What is Bancrofts rule?
- to predict which phase (oil or water) will be the continuous phase in an emulsion.
- The phase in which the emulsifier is more soluble will be the continuous phase of the emulsion.
- choose the right emulsifier based on what type of emulsion they want to create
- High HLB emulsifier = O/W
- Low HLB emulsifier = W/O
What is the purpose of Calamine 4% w/w and zinc oxide 3% w/w in aqueous calamine cream BP?
- Active ingredient
What is the purpose of purified water and liquid paraffin in aqueous calamine cream BP?
- Aqueous phase
- Oily phase
What is the purpose of Cetomacrogol emulsifying wax and Glyceryl monostearate in aqueous calamine cream BP?
- Emulsifier
What is the purpose of phenoxyethanol in aqueous calamine cream BP?
- Preservative
What is HLB matching?
- Different oils have different HLB requirements for O/W and W/O emulsions
- Use emulsifier blends if necessary
- Most stable emulsions contain more than a single emulsifier
- process of selecting emulsifiers (or a combination of them) with a (HLB) value that matches the required HLB of the oil phase in an emulsion. This helps to form a stable emulsion—whether oil-in-water (O/W) or water-in-oil (W/O).
How do you calculate HLB values requirements and how do you calculate blend of emulsifiers using HLB values?
- required HLB = required HLB * mass of both then added together
- HLB1x + HLB2(1-x) = Req HLB
What is an emulgel?
- Emulsion (O/W) or (W/O) + gel
- Gel is the continuous phase
What are the emulgel advantages?
- Incorporation of poorly water soluble drugs in water based formulation
- Non-greasy
- Good patient acceptability
- Dual release control mechanisms (both cream and gel)
- Viscous continuous phase enhances emulsion stability
- Thixotrophy enhances spreadibility: less viscous (more fluid) when subjected to stress
What is the Emulgel disadvantage?
- Entrapment of air bubbles
- Gelation happens when mixing and easy to get air bubbles in (affects dosage uniformity)
What is the polymeric emulsifier Pemulen - gelling agent and emulsifier?
- Cross linked polymers
- Alkyl acralate (hydrophobic): integrates in core of oil droplets
- Acrylic acid (hydrophilic): forms viscous gel in aqueous cont phase, de swells in contact w/ skin electrolytes to cause rapid release of oil phase
What is the type of emulsion for polymeric emulsifier Pemulen and what does it mean that its mucoadhesive?
- O/W emulsion
- Helps retain the formulations on mucus membranes
What is the purpose of the Carbomer, Glycerol and phenoxyethanol in the double base gel?
- Gelling agent
- Thickening agent (hydroxy donors help carbomer swell)
- Preservative
What is the purpose of the Sorbitan Laurate and Trolamine laurate in the double base gel?
- Emulsifier
- Neutralising agent
What are isopropyl alcohol and propylene glycol used as in Emulgel?
- Co-solvent
