Ointments Flashcards
What is an ointment?
A semi-solid dosage form, usually anhydrous with a hydrophobic oily base, intended for external application to the skin or mucous membrane.
Ointments are Occlusive
Increases skin hydration by minimising transepidermal water loss. Also enhances dermal drug penetration.
Ointment are Emollient
Suitable for dry skin
3 types of ointment
– Hydrophobic (oleaginous) ointment
– Water emulsifying ointment
– Hydrophilic (greaseless) ointment
Hydrocarbon bases for hydrophobic ointment characteristics (3)
– Occlusive—emollient effect
– Not water-washable
– Greasy
Hydrocarbon bases for hydrophobic ointment example
Petrolatum (paraffin)
Absorption bases for water emulsifying (W/O) ointment characteristics (4)
– Form w/o emulsions with skin secretions.
– W/O emulsifier
– Emollient effect
Absorption bases for water emulsifying (W/O) ointment example
Lanolin and derivatives
Water-removable bases for water emulsifying (O/W) ointment characteristics (3)
– Form O/W emulsions with skin secretions.
– O/W emulsifier
– Water-washable
Water-removable bases for water emulsifying (O/W) ointment example
Cetostearyl alcohol, cetomacrogol.
Water-soluble bases for hydrophilic ointment characteristics (2)
– Water-washable
– Non-greasy
Water-soluble bases for hydrophilic ointment example
Macrogols (polyethylene glycols = PEG)
2 basic comportments of an ointment
Drug
Ointment base
Ointments may also contain (3)
Solvent
Antioxidant
Emulsifying agent
Solvent purpose in ointment
to dissolve components, miscible with ointment base.
Antioxidant purpose in ointment
to prevent oxidative degradation. (reacidification)
Emulsifying agent purpose in ointment
for water emulsifying ointments.
Why are preservatives not generally required in ointments
As no water content.
Betnovate ointment
For relief of inflammatory and pruritic manifestations of steroid-responsive dermatoses.
White soft paraffin purpose in Betnovate
Ointment base
Liquid paraffin purpose in Betnovate
Ointment base
White soft paraffin purpose in Fucidin Ointment
Ointment base
Liquid paraffin purpose in Fucidin Ointment
Ointment base
All-rac-alpha-tocopherol purpose in Fucidin Ointment
Vitamin E antioxidant
Butylhydroxytoluene purpose in Fucidin Ointment
Antioxidant
Cetyl alcohol purpose in Fucidin Ointment
Emulsifier
Lanolin (wool fat) purpose in Fucidin Ointment
Ointment base
Rancidification
Oxidative chain reaction mediated by free radicals, changing organoleptic properties due to chemical decomposition.
What does rancidification happen to?
Particularly to oxygen-containing fats and oils derived from animals or plants.
How do antioxidants work?
Deplete free radicals, thus terminating oxidative chain reactions. Needs to be soluble in ointment base.
Example of water emulsifying ointment
Fucidin Ointment
Fucidin Ointment
Treatment of skin infections caused by sensitive strains of S. aureus, streptococcus spp and Corynebacterium minutissimum.
How to incorporate a drug into an ointment (3)
- Dissolve directly in ointment base.
- Dissolve drug in a suitable solvent, then incorporate solution into ointment base.
- Levigate solid drug into ointment base to disperse evenly, with geometric dilution.
What is levigation?
Crushing particles in presence of a fluid (levigation fluid) to reduce particle size as it being incorporated into ointment.
Two types of penetration enhancers
Physical and chemical
Chemical penetration enhancer (CPE) auxiliary equipment?
- Included as an excipient in formulation.
- No requirement for auxiliary equipment.
Physical enhancement auxiliary equipment?
Usually requires auxiliary equipment.
Physical enhancement examples
Microneedles, iontophoresis, electroporation, sonophoresis, laser ablation, thermal ablation.
Chemical penetration enhancer (CPE) increase permeability by…
Drug partitioning
What does the Lipid-protein-partitioning theory propose
Proposes that the skin has lipophilic and hydrophilic domains.
Lipid-protein-partitioning theory: lipid
Disrupting stratum corneum lipids (lipophilic domain), increasing diffusivity (D) for lipophilic drugs.
Lipid-protein-partitioning theory: Protein
Altering stratum corneum proteins (hydrophilic domain), increasing diffusivity (D) for hydrophilic drugs.
Lipid-protein-partitioning theory: Partitioning
Enhancing drug partitioning from formulation into skin, increasing partitioning (K).
Ideal properties of penetration enhancers (2)
– Chemically inert and non-toxic.
– Transient, reversible and selective penetration enhancement effect.
What type of molecules act as strong chemical penetration enhancers
Amphiphilic compounds that have a polar head group and long hydrocarbon tail.
What do Amphiphilic compounds resemble in relation to the skin?
Stratum corneum (SC) lipids
How do amphiphilic compounds work as chemicals penetration enhancers?
Insert into SC extracellular lipids to loosen packing.
Examples of amphiphilic compounds as chemicals penetration enhancers
Surfactants, fatty alcohols, fatty acids, phospholipids.
What type of amphiphilic compounds are most effective as chemicals penetration enhancers?
Unsaturated (double bond) and cis hydrocarbon tail more effective.
Why are cis isomers more effective than unsaturated (trans)?
The cis has a kink which forces open a gap in the SC lipid structure which allows small molecules to pass through.
Polar CPE are more effective on what type of drug?
Hydrophilic
Non-polar CPE are more effective on what type of drug?
Lipophilic
