creams ointments and other topical preparations Flashcards
where are ointments focused
these are focused on skin and scalp:
Topical generally means applied to any external body surface for a localised effect e.g. eye, nasal mucosa, mouth buccal mucosa, skin, scalp: all are labelled ‘for external use only’
why do we give treatment locally to the skin?
- to enhance barrier function of the skin
- Targeted delivery to specific layers of the skin e.g. fungal infections are in the outermost part of skin but for eczema need to deliver drugs deeper into the skin
- Better to give a topical formulation to treat the skin as fewer side-effects compared with oral delivery of drugs
how do formulations improve skin’s barrier function?
- Sunscreens protect against UV radiation
- Antibiotics for abrasions protect against infection
- Emollients (preparations that add moisture) improve dry skin conditions
- Moisturisers protect against drying atmospheric conditions
- Barrier creams prevent exposure of skin to harsh chemicals (e.g. for hair stylists)
skin structure = how many main layers
three
https://www.notion.so/ointments-a-bit-on-pastes-13c00bb3982d806ab7baed739c9a6282?pvs=4#13c00bb3982d81c9adc7ef36dc4c1c09
topical dosage forms to select for specific application to the skin
- Skin surface = on the skin
- Stratum corneum = in the skin
- Viable epidermis = deeper in the skin
- Dermis = underneath the epidermis
targeting the stratum corneum/above/below it
- Above or on the skin – easier target. e.g applying sunscreens, insect repellents
- Below the skin surface or into the skin – more difficult target → we treat the stratum corneum if for example fungal infections present
But if treating epidermis or dermis the formulation must allow drug to cross stratum corneum = percutaneous absorption of drugs
Types of topical dosage forms currently available?
- Semisolids = halfway between solid and liquid and include: Ointments, pastes, creams, lotions, jellies, gels, liniments, collodions, plasters
- Topical solutions
- Soaps/shampoos
- Tinctures
- Powders
- Aerosols/Foams
- Topical patches
Occlusive vs non-occlusive topical formulations
Occlusive = the formulation prevents water movement out of the body.
Occlusive = the formulation prevents water movement out of the body.
An occlusive preparation increases skin hydration and moisture content by “locking in” the water present in the body
- Good for dry skin but bad for infected skin
- Enhances skin barrier as forms a “shield” on skin
- Good penetration of drugs through the skin
what are the 2 types of ointments for the skin:
hydrocarbon and water soluble ointments
what are ointments:
ointments are semisolid preparations intended for external application to the skin or mucous membranes.
oils/ waxes etc found in ointments?
- Soft paraffin is most common ingredient but liquid paraffin (mineral oil) or hard paraffin used to thin or thicken formulation as needed. The two types of soft paraffin are yellow petrolatum vaseline, and white petrolatum (bleached to remove yellow colour)Other types of oils that may be found in hydrocarbon ointments:
- vegetable oils, from plant sources e.g. castor, olive: oils may be thickened with a high melting point material
- synthetic oils, e.g. silicone oils used as water repellents
- isopropyl myristate, e.g. semisynthetic and similar to the vegetable oils in its properties and uses.
properties of hydrocarbon ointments
- Occlusive
- Emollient: Hydrate skin due to moisture accumulation
- Skin hydration keeps skin supple
- Difficult to remove, just water does not work
- Greasy
- Good if drug not stable in water
water soluble ointment / also can be diff ones that are washable tho
- Examples = macrogol ointment (polyethylene glycol ointment). This is a polymer so we can control the length of the polymer to produce whatever type of preparation we want.
- longer the chain length of the polymer = higher the melting point of the ointment.
- Can mix short and long chain polymers to produce different ointments with different melting points
properties of water-soluble ointments
- Water soluble
- Washable
- Non-greasy
- Non-occlusive or not as occlusive as hydrocarbon ointments so they do not lock water in as well as hydrocarbon ointments
what are pastes
- Ointments where we can have 20 to 50% of solid material
- For this reason they are stiffer than ointments
paste characteristics
- Good protective barrier – water impermeable
- Prevent dehydration e.g. Pastes are used to prevent windburn on Skiers
- Pastes are used to prevent nappy rash – absorb ammonia from break down of urine
Why are creams popular for topical application?
- Good delivery system for many drugs
- Good patient acceptability
- Spread easily
- Not as occlusive as ointments
- For O/W creams, water evaporates to leave a thin “film” on the skin
creams have 2 phases which are
- oil phase
- water phase
creams can either be o/w or w/o: extra info
Either oil in water (O/W) or water in oil (W/O): Oil droplets suspended in water or water droplets suspended in oil
- emulsifiers keep the droplets suspended
There are some W/O creams but most common to have O/W creams used for drugs
note: creams need a preservative to stop contamination because water is present in creams
- Name comes from creamy appearance → these aren’t as “stiff” or “sticky” as ointments
what do we use to make creams
emulsifiers, which we select based on if its a w/o cream or a o/w cream
w/o cream details e.g. what do they include?
- w/o emulsifiers include wool fat (lanolin) which is a pale, yellow sticky material composed of fatty acid esters of cholesterol and other sterols.
- It is similar to human sebum but can cause sensitisation in some patients.
- Wool alcohols (lanolin alcohols) = w/o emulsifier
- It is richer in cholesterol and lanesterol and freer of impurities than wool fat
- Hydrous wool fat (hydrous lanolin) is 7 parts wool fat, 3 parts water and is softer than wool fat or wool alcohols
- Beeswax is a traditional w/o emulsifier composed of fatty acid esters and long chain alcohols
o/w: emulsifiers and creams
- Emulsifying waxes – there are three types
- Each one has two ingredients – cetostearyl alcohol (CSA) and a surface active agent
1. Emulsifying wax BP contains sodium lauryl sulphate and CSA (1:9)
2. Cetrimide emulsifying wax BPC contains cetrimide and CSA (1:9)
3. Cetomacrogol emulsifying wax BPC contains cetomacrogol 1000 and CSA (8:2)
what are gels
these are solid/semisolid preparations, that require a gelling agent
Gelling agents used = natural/synthetic
- natural gelling agents → tragacanth, pectin, alginate
- synthetic gelling agents → synthetic polymers e.g Carbomer, Cellulose
Gels are usually transparent or translucent
how gels and gelling agents work
- The gelling agent forms a cross-linked network in liquid
→ So gels are a dispersion of liquid within a solid where the solid is the continuous phase and the liquid is the disperse phase
Hydrogels: based on water and are formed by a hydrophilic polymer swelling in water
