Below is the formula of a softening cream called “Cremor leniens”:

White beeswax ………………………………………………….7.0 g

Cetyl palmitate ………………………………………………….9.0 g

Refined sunflower oil ………………………………………53.5 g

Virgin castor oil ………………………………………………….5.0 g

Glycerol monostearate 40-50 ………………………….5.5 g

Purified water …………………………………………………20.0 g

Methylparaben ……………………………………………….0.04 g

Propylparaben ………………………………………………..0.01 g

Propyl gallate ………………………………………………….0.02 g

Geranium essential oil ……………………………………0.3 ml

 

Questions:

  1. Creams are semisolid emulsions for topical use. How would you proceed when preparing this cream? Three methods of emulsion preparation are described below. Which one would you use in the case of Cremor leniens?
    • Methods of preparation of emulsions:
      • Wet gum method (English method): emulsion is formed by mixing the emulsifying agent with a dispersion medium in which it dissolves. This is then mixed with a dispersed phase.
      • Dry gum method (continental method): order of mixing is different; emulsion is formed by mixing the emulsifying agent with the dispersed phase in which it dissolves; and this is then mixed with the dispersion medium.
      • In situ soap method: emulsifying agent is produced during the preparation of emulsion (not added from outside).
  2. Emulsion are generally two-phase systems with an internal phase and an external phase such as oil-in-water (o/w) and water-in-oil (w/o). Emulsifier is used to maintain physical stability of emulsion. Please identify the emulsifier in the preparation of Cremor leniens and describe its mechanism of action. Based on the used emulsifier, which type of emulsion is it?
  3. Two more components can help maintain the physical stability. Their mechanism of action differs from the one employed by the emulsifier. Please indicate the general name of this kind of substances, their mechanism of stabilisation and identify them in the composition of the Cremor leniens.
  4. Which components are used to ensure microbial stability of the cream? Are there any antioxidants?
  5. In the formula of Cremor leniens, could the total amount of purified water and both parabens be replaced with the same amount of paraben preserved water (composition shown below)? Why? 
    • Paraben preserved water
    • Metylparaben                                  0.67 g
    • Propylaparaben                              0.33 g
    • Purified water               up to 1 000.0 g
  6. Two oils are used in the preparation. Which one is more hydrophilic and why?

 

   
Structure of major triglyceride present in castor oil
(source: wikipedia.org)
Structure of major triglyceride present in sunflower oil

(source: wikipedia.org)

7.    Contrary to Ungentum leniens (softening ointment), Cremor leniens does not have a cooling effect. Based on the composition of Ungentum leniens below, could you explain why it has a cooling effect after application on the skin?

Composition of Ungentum leniens : borax (sodium borate), white beeswax, cetyl palmitate, refined sunflower oil, virgin castor oil, geranium essential oil, purified water

 

Answers:

  1. The cream is prepared by wet gum method (English method) as the emulsifier is firstly dissolved in oil phase (the soluble phase).
    • A hot solution of parabens in water is prepared.
    • Beeswax, cetyl palmitate, both oils and glycerol monostearate are melted in the mortar. Propyl gallate is then dissolved in the melted mixture.
    • The solution of parabens is added to the melting step by step. The emulsified system is homogenised until cold.
    • The amount of evaporated water is used to adjust the weight of the cream.
    • Finally, geranium essential oil is added to the cool cream.
  2. Glycerol monostearate is an emulsifier. It acts on the interface by decreasing the interfacial tension. This cream is water-in-oil (W/O), it´s an hydrophobic cream.
  3. Besides emulsifier, quasi emulsifiers increases viscosity of the outer oil phase and thus helps to maintain the system stability. In Cremor leniens, these are white beeswax and cetyl palmitate.
  4. Both parabens are antimicrobial components and propyl gallate is an antioxidant.
  5. Parabens preserved water contains lower amount of parabens compared to what is required for compounding Cremor leniens. The increased amount of parabens is due to the fact that parabens are lipophilic substances and thus have some affinity to oil phase. Part of the entire amount can then pass to the oil phase. In order to ensure sufficient concentration of parabens in water phase, we should use the prescribed amount of parabens, not Parabens preserved water.
  6. Castor oil is more hydrophilic. Both oils are triglycerides, however, esterified with different fatty acids. Sunflower oil contains mainly triglycerides derived from linoleic and oleic acid. Castor oil has usually three ricinoleic fatty acids. Ricinoleic acid differs from other fatty acids because of hydroxyl functional group on C12 that increases its hydrophilicity.
  7. Ungentum leniens does not contain emulsifier, only two quasi emulsifiers, so the system is not stable enough. After application, the emulsified system disrupts and the released water has a cooling effect while evaporating.