Pharmacology Flashcards
When is topical administration usually used?
Superficial skin disorders Skin infections Itching Dry skin Warts
What are the vehicles for topical administration?
Lotions Creams Ointments Gels Pastes Powders
What is Fick’s law of diffusion?
Rate = permeability x concentration of drug in the vehicle
What does permeability of a drug take into account?
Partition co-efficient
Diffusion co-efficient
Length of the diffusion pathway
What is the partition co-efficient?
The movement of the drug from vehicle into the stratum corneum
What type of drug and vehicle are needed to reach systemic capillaries?
Lipophillic (easily moves through the skin)
Lipophilic or hydrophilic vehicle
What type of drug and vehicle are needed for superficial skin conditions and why?
Hydrophilic drug in lipophilic base Only partitions (moves through skin) weakly
What type of drug and vehicle would not penetrate the skin?
Hydrophilic drug and base
What are excipients and why are they used in vehicles?
Substances that can enhance hydrophobic drug solubility to enhance absorption
What is the advantage to transdermal patches?
Excess non-dissolved drug can be included to increase duration of effectiveness and provide a constant rate of delivery
What can the partition co-efficient be improved by?
Hydration of the skin by occlusion by ointment or cling film
Inclusion of excipients
What aspects of the nature of skin influence the absorption of topical drugs?
Thickness of the site of application
Hydration of the skin
Integrity of the epidermis
What skin conditions are topical steroids used treat?
Atopic eczema
Psoriasis
Pruritis
How do topical steroids work?
Anti-inflammatory
Immunosupressant
Vasoconstricting
Anti-proliferating for keratinocytes and fibroblasts
What are the categories of topical steroid?
Mild
Moderate
Potent
Very potent
In what vehicles are topical steroids available?
Lotion
Cream
Ointment
What are the side effects of high potency steroids?
Steroid rebound
Skin atrophy
Systemic effects
Spread of infection due to immune suppression
Steroid rosacea
Stretch marks and small superficial dilated blood vessels (telangectasia)
What is the mechanism of action of topical steroids?
Signal via nuclear receptors
Lipophilic molecules, enter by diffusion
How does subcutaneous administration work?
Drug inserted into the fatty (adipose) tissue just beneath the surface of the skin
Drug reaches the systemic circulation by diffusion into either capillaries or lymphatic vessels
What are the advantages of subcutaneous administration?
Absorption is slow
Preferred for many protein drugs and oil-based drugs
Can be used to introduce depot of drug that is slowly released into circulation
Simple and relatively painless
What is the disadvantage of subcutaneous administration?
Injection volume limited
What is transdermal drug delivery?
Drug is incorporated into an adhesive patch applied to the epidermis
Drug absorption partially controlled by a drug release membrane
Absorption occurs by diffusion across cutaneous barrier
What are the drugs that are most suitable for transdermal drug delivery?
Low molecular weight
Moderately lipophilic
Potent
Short half-life
What are the advantages of transdermal delivery?
Steady rate of drug delivery Decreased dosing frequency Avoidance of first-pass metabolism Rapid termination if half-life too short User-friendly, convenient and painless
What are the disadvantages of transdermal delivery?
Relatively few suitable drugs
Allergies
Cost
What are examples of drugs that can be given by transdermal delivery?
Scopolamine
Nicotine
GTN
What are the advantages and disadvantages of topical skin treatments?
Advantages: direct application, reduced systemic effects
Disadvantages: time consuming, correct dosage can be difficult, messy to use
What are the vehicles that can be used to apply drugs?
Gels Creams Ointments Pastes Lotions Foams
What is a cream?
Semisolid emulsification of oil in water
What are the benefits of cream?
High water content so cools and moisturises
Not greasy
Easy to apply
Cosmetically acceptable
What is an ointment?
Semisolid grease/oil
What are the advantages and disadvantages of ointments?
Possibility of contamination so can’t share
Restrict water loss
But greasy so less cosmetically attractive
What is a lotion?
Liquid suspension or solution of medication water, alcohol or other liquid
What are lotions used to treat?
Scalp conditions and other hair bearing areas
What are gels?
Thickened aqueous liquids containing high molecular wight polymers
What are gels used to treat?
Scalp, hair bearing areas, face
What are pastes?
Semisolids that contain finely powdered material
What are the disadvantages of pastes?
Stiff, greasy, difficult to apply
What are the benefits of pastes?
Protective, occlusive, hydrating
Can protect surrounding skin
Often used in cooling, drying soothing bandages
What are foams?
Colloid with two or three phases, usually a hydrophilic liquid in continuous phase with a foaming agent
What are the advantages of foams?
Increased penetration of active agents
Spreads easily over large areas of skin with no greasy/oily film
What is the action of emollients?
Enhance rehydration of the epidermis
What are emollients used for?
All dry or scaly conditions
When is wet wrap therapy used?
For very dry skin, mostly for children
When are calcineurin inhibitors used?
As alternative to steroids in eczema
What are the types of anti-invectives?
Antiseptics
Abtibiotics
Antivirals
Antifungals
What is the action of antiseptics?
Bacteriostatic or bactericidal
What are the uses of antiseptics?
Recurrent infections
Skin cleansing
Wound irrigation
What are the skin uses of antibiotics?
Acne and rosacea
Skin infections
Infected eczema
What are the disadvantages of using antibiotics in skin conditions?
Resistance
Sensitisation
Only use if you have to
When are antivirals used in skin conditions?
Herpes simplex virus cold sores
Eczema herpeticum
Herpes Zoster (shingles)
When are antifungals used in skin conditions?
Candida
Dermatophytes (ring worm)
When are keratolytic agents used?
Viral warts
Hyperkeratotic eczema and psoriasis
Corns and callouses
To remove keratin plaques in scalp
What is an example of a keratolytic agent?
Salicylic acid ointment
How are warts treated?
Mechanical paring plus: Salicylic acid (keratolytic) Formaldehyde Silver nitrate Cryotherapy
How is psoriasis treated?
Emollients and a choice of: Coal tar Vitamin D analogue Keratolytic Topical steroid Dithranol
Which treatments are used in stable chronic plaque psoriasis?
Coal tar
Vit D analogues
Dithranol
What treatments are used in scalp psoriasis?
Greasy ointments to soften scale
Tar shampoo
Steroids in alcohol base or shampoo
Vit D analogues
What treatments are used in psoriasis in axilla?
Topical steroids for face, flexures, groin/genitals
Consider combination antibacterial and anti fungal
Calcineurin inhibitors
What are topical treatments for superficial basal carcinomas?
5-fluorouracil
Imiquimod
What are possible side effects of topical therapies?
Burning or irritation
Contact allergic dermatitis
Local toxicity
Systemic toxicity
