Topicals Flashcards
What does topical mean?
Applied to any external body surface for a localised effect e.g. eye, nasal mucosa, skin, scalp
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 improve dry skin conditions
- Moisturisers protect against drying atmospheric conditions
- Barrier creams prevent exposure of skin to harsh chemicals
Skin Structure - 3 main layers
Stratum corneum is outer
layer of epidermis
Skin cells begin life in
the stratum basale layer
of the epidermis
Blood vessels are
present in the dermis
but not the epidermis
Sweat glands, hair follicles
and sebaceous glands
originate in the dermis.
The subcutaneous layer
is fatty tissue that acts as
“cushion” for the skin
What topical dosage form should you select for application to the skin?
- Skin surface = on the skin
- Stratum corneum = in the skin
- Viable epidermis = deeper in the skin
- Dermis = underneath the epidermis
- Do you need to treat the skin appendages = hair, sweat glands, sebaceous glands, nails
Target above the stratum corneum (SC), to the SC or below SC
- Above or on the skin – easier target. This is where we apply sunscreens, insect repellents
- Below the skin surface or into the skin – more difficult target
- 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
What type of topical dosage forms are 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 means that the formulation prevents water movement out of the body. So 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 ointments?
Semisolid preparations intended for external application to the skin or mucous membranes
2 types of ointments for the skin
- Composed of hydrocarbons (not water soluble)
- Water soluble ointments
Types of soft paraffin hydrocarbons
- Yellow petrolatum (Petroleum Jelly) Vaseline
- White petrolatum (white petroleum jelly) has been bleached to remove yellow colour
What other types of oils are found in hydrocarbon ointments?
Vegetable oils from plant sources e.g. peanut, castor, olive, coconut. These oils may be thickened with a high melting point material such as cetosteary alcohol
Synthetic oils such as silicone oils (Dimethicone BP) used as water repellents.
Isopropyl myristate is 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 ointments
These ointments are water soluble or washable
Examples include 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.
The longer the chain length of the polymer the higher the melting point of the ointment.
Can mix short and long chain polymers to produce different ointments with different melting points
Examples of products with water soluble ointment bases
Bactroban ointment contains mupirocin - used for treatment of skin conditions
Iodosorb ointment consists of a form of ionine in a macrogol ointment base, used for wound management
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
Pastes
We can have 20-50% of solid materials
Stiffer than ointments
Good protective barrier - water impermeable
Prevent dehydration e.g. pastes are used to prevent windburn
Pastes are used to prevent nappy rash - absorb ammonia from break down of urine
Creams
Two phases, oil phase and a water phase
Either o/w or w/o
Need emulsifiers to keep the droplets suspended
Need a preservative to stop contamination because water is present in creams
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
How are emulsifiers used to make creams?
Select emulsifier depending on whether a w/o cream or a o/w cream is needed
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
Emulsifiers in w/o creams
- Wool alcohols
- Richer in cholesterol and lanesterol and freer of impurities than wool fat
- Hydrous wool fat 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
Examples of w/o creams
Drapolene cream for nappy rash
Boots chilblain cream
Emulsifiers in o/w creams
- Emulsifying waxes - 3 types:
Each one has 2 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)
Miscellaneous emulsifiers
- Calcium soaps are produced by mixing a fatty acid with lime water (calcium hydroxide solution) to form a soap. They are used to form w/o emulsions
- Synthetic surface active agents can also be used. Low HLB materials produce w/o emulsions and higher HLB materials give o/w emulsions
- HLB – hydrophilic lipophilic balance
