Unit 2 - Topical Formulations Flashcards
Where is hairy skin found?
Everywhere except palms of hands and soles of feet
What is the outer dead layer of skin called
Stratum corneum
What is the structure of the epidermis?
Keratinocytes
Melanocytes
Langerhans cells
What is the structure of the dermis?
Blood vessels
Sweat glands
Base of hair follicles
Sense cells
What is the function of the skin?
- active barrier (adapts to conditions)
- regulates body temperature
- mediates sensation
- expresses emotion (reddening)
- identifies us
How can skin be damaged?
- mechanically (cuts)
- chemically (burns)
- biologically (microbes)
- radiation (UV)
Why might applications be put onto the skin?
- Manipulate the barrier to improve its function
- infection
- protection
- emollient (moisturise) - Local treatment
- anti-inflammatory
- symptomatic relief - Systemic treatment
- transdermal drug delivery (patches/topical)
- NSAIDs
- motion sickness
- angina
- hypertension
What are the five targets of topical delivery?
- Designed to stay on the surface of the skin barrier
- protective layer
- antibacterial/antifungal - Deliver to stratum corneum
- emollient
- hyperkeratosis - Deliver to skin appendages
- hyperhidrosis
- acne
- antibiotics
- transfollicular absorption - Deliver to epidermis/dermis (keratinocytes)
- steroids
- anti inflammatories
- antipruritics (anti-itching)
- anaesthetics
- prior to tattoos/infections - Deliver to blood supply
- systemic circulation
What factors affect topical delivery?
- skin age
- skin delivery
- skin region
- skin metabolism
- species
How does skin age affect drug delivery?
Collagen structure changes
- thickness of layers
- elasticity
How does skin condition affect drug delivery?
Hydration - cracked skin affects the barrier
How does skin region affect drug delivery?
- plantar (hairless)
- palmar (hairless)
- scrotal
- scalp
- arm
- leg
- trunk (torso)
How does skin metabolism affect drug delivery?
- defensive enzymes
- flora on skin
- oils on skin
How does species of skin affect drug delivery?
Pre-clinical studies needs to use skin which is very similar to human. Porcine is often used
Give examples of topical formulations
- topical semi-solid preparations (e.g. creams, gels, ointments, pastes)
- lotions
- patches
- powders
- microneedles
- sprays
What is a topical semisolid formation?
Semi-solid preparations for cutaneous application are intended for local or transdermal delivery of active substances or for their emollient or protective action
What is a semi solid?
Formulation which possess rheology with a mixture of solid and fluid behaviour
- solids retain shape when acted upon by external stimuli
- liquids flow indefinitely
What is the structure of a cream
- oily phase
- aqueous phase
Give examples of topical semi-solid preparations
Ointments
Pastes
Creams
Gels
Describe the properties of ointments
- water emulsifying (e.g. wool alcohols ointment BP)
- hydrophobic (e.g. calamine ointment BP)
- hydrophilic (e.g. macromolecules ointment BP)
Describe the properties of creams
- hydrophobic (w/o)
- hydrophilic (o/w)
Describe the properties of gels
- hydrophobic
- hydrophilic
Describe an ointment
Soft, semi solid preparation
- single phase base in which solids or liquids may be dispersed
- emollient action without absorption through the skin
- protective effect against environment
- intended to adhere to the skin and mucous membranes for localised delivery
What are the two types of ointment used in topical delivery?
- occlusive
- non-occlusive
What is transepidermal water loss?
Loss of water through the skin naturally - not just through sweating
what does occlusive mean ?
To close, obstruct, or prevent the passage
What effect does an occlusive ointment have on the skin?
Stops water loss
Moisturises skin
What effect does a non-occlusive ointment have on the skin?
Allows water loss - absorbs water into the ointment which passes through the ointment
Why do topical drugs get delivered to different extents?
Different ointments have different properties so penetrate to different degrees through the skin
What are the six main types of ointment bases?
- hydrocarbons
- fats and fixed oils
- silicones
- absorption bases
- emulsifying bases
- water-soluble bases
Describe hydrocarbons as an ointment base
Hard, soft and liquid paraffins
What type of ointment base is the most widely used?
Hydrocarbons
How does a hydrocarbon ointment base work?
Forms a greasy film on the skin (occlusive), reducing moisture loss and improving hydration (including absorption)
- water comes to the skin surface which helps the water soluble drug be absorbed
What are the advantages of using hydrocarbons as an ointment base?
- relatively inert
- few incompatabilities
How can a hydrocarbon ointment base be made easily spreadable with consistent rheological properties?
Soft paraffin is often mixed with liquid and hard paraffin
Why do patients need to regularly hot wash their clothes which are in contact with ointment?
They absorb flammable bases which can then catch fire easily
Give some examples of fats and fixed oils as an ointment base
Vegetable origin
- peanut (arachis)
- sesame
- olive
- cotton seed
- almond
Why is there variation in fats and fixed oils as an ointment base?
- batch
- growing conditions
- country of origin
What types of fats make up fats and fixed oils as an ointment base?
Mixtures of saturated and unsaturated fats
How can fats and fixed oils as an ointment base decompose?
- exposure to air
- exposure to light
- increased temperature (rancidity)
What is rancidity in fats and fixed oils as an ointment base increased by?
Metallic impurities
- metal ions in source or excipients used
Describe fats and fixed oils as an ointment base
Occlusive and sticky
What is the advantages of using fats and fixed oils as an occlusive ointment base?
Stops trans-epidermal water loss
What are the disadvantages of using fats and fixed oils as an ointment base?
Allergies
- peanut oil (arachis)
- sesame oil
What is the function of silicones as an ointment base?
Water repellent
- used in barrier creams to protect against water soluble irritants
