Topical Products Flashcards
How does the stratum corneum act as a barrier?
*has alternating amorphous lipophilic and hydrophilic layers (majority lipophilic cells)
*contain keratin and fat
*40% water, 40% protein
*dense tissue, swells in water to many times own thickness
*cells stacked in vertical columns to form cohesive laminae
*each cell has a proteinaceous envelope instead of lipid bilayer membrane
*40-70 hair follicles per square cm-secrete sebum
*200-250 sweat ducts per square cm- temp control
How can topical products act on the stratum corneum?
*increase barrier ie sunscreen
*reduce barrier ie drug delivery
*treat damaged barrier ie antibiotics
*restore physical characteristics ie emollients, moisturisers
How are drugs systemically absorbed from the skins surface?
*drug percolates deep into dermis to micro-circulation
*micro circulation acts as drug sink- carry’s drug away into systemic circulation leaving a near zero drug level in dermis
*if skin damaged, rapid systemic absorption can occur via topical route-care required
Why is topical therapy usually free from systemic reactions?
Dilution factor following absorption from topical route approx 1000
What factors promote percutaneous drug absorption?
*stratum corneum barrier compromised by disease
*raised skin temp- increased drug diffusion
*chemical manipulation of barrier
*maximised drug concn in solution in applied surface film
What are examples of topical dosage forms?
*aerosols
*powders
*emulsions
*transdermal patches
*SEMI SOLID PREPARATIONS- Ointment, cream, paste, gel
What is an advantage of using semi solids in topical drug delivery?
Remains localised at application site until mechanical force applied
Applied force causes permanent deformation in applied formulation- hence why semi solid
What are hydrocarbon ointments?
*Hydrocarbon based semi-solids
*base-higher melting solid at room temp (matrix former) + fluid component.
*matrix former- mixture of C30-C50 hydrocarbons and C16-C30 hydrocarbons
*made by fusion (melting)
In a hydrocarbon ointment , how is the stiffness of the final product determined?
*the relative proportions of two fluid and solid components
*speed of cooling- slow cooling=larger crystalline structure in matrix former=matrix less coherent=more fluid base
How are non hydrocarbon ointment bases made?
Silicone oil + a wax (matrix former) followed by cooling
Good barrier properties to moisture- excellent emollients
What type of lesions are hydrocarbon ointments suitable for?
Dry (has water retaining properties)
How are ointments prepared?
*oil and wax heated to between 60-80°
*drug component added (if insoluble milling process needed)
*system cooled with gentle stirring (to avoid air trapping)
What is a paste?
An ointment with a high loading of insoluble solid-stiff
Less greasy
Good protective barrier- absorb irritating agent before reach skin
Dry to clear film
Used in sun screens and skin hydration
What gives creams their creamy white appearance?
The internal phase reflects light
What is a cream?
o/w emulsion
Oil phase made of long chain alcohols, esters, acids
