Derm 5 Flashcards
(36 cards)
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What are the learning outcomes of the topical formulations lecture?
Describe creams and ointments, understand scientific principles in their manufacture, and explain the role of excipients.
What are pharmaceutical creams?
Semi-solid emulsions for external application, usually oil-in-water (o/w) emulsions; can also be water-in-oil (w/o).
What are the two phases of a cream?
A lipophilic (oily) phase and an aqueous (water) phase, with one dispersed as droplets in the continuous phase.
What are key formulation considerations for creams?
Ensure sufficient drug dose, homogeneous dispersion, drug permeation across the skin barrier, and stable emulsion.
What helps ensure homogenous dispersion of insoluble drugs in creams?
Good solubility or incorporation by trituration (grinding to fine powder) or levigation (wet grinding).
What molecular properties must a drug have to cross the skin barrier?
Molecular weight < 500 and log P (lipophilicity) between 1–4.
How are creams prepared?
Dissolve ingredients in oil and aqueous phases separately (60°C), mix at same temperature, stir to form emulsion, cool slowly.
What is trituration?
Size reduction by grinding solid particles to ensure even dispersion in the formulation.
What is levigation?
Wet grinding of insoluble solids in the presence of a levigating agent to improve dispersion in creams or ointments.
What are the essential components of a cream?
Active pharmaceutical ingredient (drug), oil phase, aqueous phase, emulsifier(s).
Why are preservatives added to creams?
To prevent microbial contamination due to water content.
Name common preservatives used in creams.
Phenoxyethanol, parabens, benzoic acid, benzyl alcohol, chlorocresol.
What is the purpose of antioxidants in creams?
Prevent oxidation of oily components; e.g. vitamin E (α-tocopherol acetate), BHT.
Why are pH regulators used in creams?
Maintain pH within a narrow range to minimise drug degradation.
Name examples of pH regulators.
Citric acid, sodium hydroxide (buffer system).
What do density modifiers do in cream formulations?
Prevent phase separation (creaming); examples: propylene glycol, glycerol, dextrose.
What is aqueous calamine cream BP used for?
Symptomatic relief of mild skin conditions; contains zinc oxide and iron oxide.
How are insoluble solids incorporated into calamine cream?
By trituration after cooling to avoid heat degradation.
What are ointments?
Semi-solid preparations, often anhydrous, with hydrophobic oily bases for external use.
What is the main function of ointments?
Form an occlusive barrier to prevent moisture loss and enhance drug penetration.
Name the four types of ointment bases.
Hydrocarbon bases, absorption bases, water-removable bases, water-soluble bases.
What is an example of a hydrocarbon base?
Petrolatum (mixtures of hard paraffin, white soft paraffin, liquid paraffin).
What is the function of absorption bases?
Soak up water to form w/o emulsions while remaining semi-solid; e.g. lanolin.
