Ointments, creams, pastes and gels Flashcards
Advantages and disadvantages of dermatological preparations
Advantages
* Allows direct application to and retention at target site
* Drug is less prone to segregation than liquid formulations
Disadvantages
* Drug dose is not readily quantifiable
* Some products are intricate formulations with complex structural elements that can be difficult to stabilise
Ideal features of dermatological preparations
Optimised drug delivery
Physically stable
Chemically stable
Production can be readily scaled up
Compatible with skin condition
Non-sensitising; low irritation potential
Cosmetically acceptable and user-friendly
Functions of dermatological prep
Emollient
Symptomatic relief
Protective
Drug delivery vehicle
What are ointments
Semisolid, often greasy external preparations
* No water
Drug is dissolved or dispersed in ointment base
Classification
* Fatty
* Absorption base
* Emulsifying base
* Water-soluble base
What are fatty ointments
Water-immiscible hydrocarbon or fat bases
Provide emollient and occlusive effects
Formulation
* Hard, soft and liquid paraffins
* Solid fats and fixed oils
* Silicone oils
* Additives
o Antioxidants
o Chelating agents
E.g. Petrolatum
What are absorption bases fatty ointments
HC base with w/o emulsifier
Emollient but not as occlusive as fatty bases
Emulsifiers
* Wool fat
* Fatty alcohol
* Sterols
* Span
E.g. Simple oinment APF
What are emulsifying bases fatty ointment
HC base with o/w emulsifier
Water-miscible
Examples
Anionic - Sod lauryl sulfate
Cationic - cetrimide
Non-ionic - cetomacrogol, cetostearyl alcoholc
What are water-soluble bases
Water-miscible, non-greasy bases
Prepared from mixtures of high and low mw polyethylene glycol (PEG)
E.g. Macrogol ointment
Cream characteristics
High water content
May contain charged emulsifiers
- Anionic - sodium lauryl with cetostearyl alcohol
- Cationic - cetrimide with cetostearyl alcohol
- Non-ionic - cetomacrogol with cetostearyl alcohol
Explain the formulation of creams
Comprise combination of fatty amphiphile and surfactant
Formulated with excess emulsifiers
* Form films at oil-water interphase and in bulk water phase
Fatty amphiphile forms liquid crystalline gel structures in water
* Addition of surfactant leads to swelling of crystalline gel network
Explain the gel network theory
o/w creams are influenced by swelling properties of crystalline gel network formed when there’s excess emulsifier required to form an interfacial film at the oil/water interface
Gel netowrk in emulsion achieved with
- Ionic surfactant
- Non-ionic surfactant
What are pastes and what are its characteristics
Semisolid stiff preparations with high powder content in a fatty base
Characteristics
* Feels less greasy than ointments
* Leaves opaque film upon application
o Localised drug action
o Protective
* Effective at absorbing skin secretions
What are gels and what are its characteristics
Liquid contained within semisolid networks
* High water content - 10-20%
Suspensions of small inorganic particles interpenetrated by liquid phase
Solutions of large oranic molecules
What are excipients for semi-solid formulations
What are methods of manufacture for semisolids
State quality standards and compendial requirements for semi-solid
