Pharmacology Flashcards
Major routes of administration for diseases of the skin
Topical, transdermal, subcutaneous/depot
Other epithelial routes for drug administration
Airways, conjunctival sac, nasal mucosa, vaginal
Most important barrier to drug penetration into the skin or diffusion across it
Stratum corneum
Brick and mortar model of stratum corneum
‘bricks’ - corneocytes containing keratin macrofilaments embedded in a filaggrin matrix surround by cornified envelop
‘mortar’ - multiple lamellar structures of intercellular lipids. Intercellular glue that can also act as a reservoir for lipid-soluble drugs
Drug delivery into and across the stratum corneum is a/an __ process, mediated by __ when the drug is applied topically
Active, diffusion
Topical route of administration
Drug is applied in a pharmacologically inactive vehicle to the skin
The topical route of administration is most often used local effects in the treatment of what?
Superficial skin disorders (psoriasis, eczema) Skin infections Itching Dry skin Warts
Vehicles for topical route of administration from greatest water content to least
Lotions Creams Ointments Gels Pastes Powders
What is the choice of vehicle dilated by?
Physiochemical properties of the drug and the skin condition
Factors influencing the absorption of topically applied drugs
Rate of absorption
Nature of the skin
Drug/pharmaceutical preparation
What does rate of absorption depend on?
Permeability coefficient and concentration of drug in the vehicle
Lipophilic drug in a lipophilic base is soluble/insoluble in the vehicle and soluble/insoluble in the skin
Lipophilic drug in a lipophilic base is soluble in the vehicle and soluble in the skin and partitions between the two
Lipophilic drug in a hydrophilic base is more/less soluble in the skin
Lipophilic drug in a hydrophilic base is more soluble in the skin and so preferentially partitions into it
Hydrophilic drug in a lipophilic base has good/limited solubility in both the vehicle and the skin
Hydrophilic drug has limited solubility in both the vehicle and the skin and partitions into it weakly
Hydrophilic drug in hydrophilic base is soluble/insoluble in the vehicle and soluble/insoluble in the skin
Hydrophilic drug in hydrophilic base is soluble in the vehicle but insoluble in the skin and so remains on the surface
How can drug solubility and absorption be enhanced?
By inclusion of excipients within the vehicle
What provides the driving force for skin penetration for drugs applied topically?
The fraction within the vehicle solubilised
Advantage of using transdermal patches
They include excess, non-dissolved drug which can increase duration of effectiveness and provide a constant rate of delivery
Topically applied drugs are generally well/poorly absorbed
Poorly absorbed - only a small fraction partitions into the skin
Physical and chemical factors that can improve partitioning of topically applied drugs
Hydration of the skin by occlusion
Inclusion of excipients that increase solubility of hydrophobic drugs
Factors relating to nature of the skin that influence the absorption of topically applied drugs
Site of application (thickness of stratum corneum)
Hydration of the skin
Integrity of epidermis
Glucocorticoids are widely used topically in which conditions?
Eczema, psoriasis and pruritus
Formulations of topical glucocorticoids available
Lotion, cream, ointment
Adverse effects of long term use of high potency steroids
Steroid rebound Skin atrophy Systemic effects Spread of infection Rosacea Stretch marks and small superficial dilated blood vessels
Main nuclear receptor glucocorticoids signal via
GR alpha
What do glucocorticoids bind with once in the cytoplasm and what does this produce?
GR alpha producing dissociation of inhibitory heat shock proteins and the activated receptor translocates to the nucleus aided by importins
Subcutaneous route of administration
Drug delivered by a needle, inserted into the adipose tissue just beneath the surface of the skin
Advantages of subcutaneous route of administration
Absorption is fairly slow (advantage/disadvantage)
Relatively simple and fairly painless
Can be used to introduce a depot of drug under the skin that is very slowly released into circulation
Route of administration of many protein drugs and suitable for administration of oil-based drugs
Disadvantages of subcutaneous route of administration
Injection volume limited
Absorption is fairly slow (advantage/disadvantage)
Why is the skin an attractive route for drug administration for systemic effect
Application is simple and non-sterile
Avoids first pass metabolism
Potentially allows for a steady state concentration of drug to be achieved over a prolonged period of time
Transdermal drug delivery
The drug is usually incorporated into an adhesive patch applied to the epidermis
Features of drugs that make them suitable for transdermal drug delivery
Low molecular weight
Relatively lipophilic
Potent
Of relatively brief half-life
Advantages of transdermal drug delivery
Steady rate of drug delivery Decreased dosing frequency Avoidance of first pass metabolism Rapid termination of action (if half-life short) User friendly Convenient Painless
Disadvantages of transdermal drug delivery
Few drugs suitable for this method
Allergies
Costly
Examples of drugs that can be used by the transdermal drug delivery method
GTN
Fentanyl
Buprenorphine
Estradiol
Advantages and disadvantages of topical treatments
Advantages - direct application, reduced systemic effects
Disadvantages - time consuming, correct dosing can be difficult, messy to use
What is a cream?
Semisolid emulsion in water, containing emulsifier and preservative
Creams have a high/low water content
High
Advantages of creams
Cool and moisturise
Non-greasy
Easy to apply
Cosmetically acceptable
What is an ointment?
Semisolid grease/oil (soft paraffin) with no preservative
Advantages and disadvantages of ointments
Advantages - occlusive and emollient, restrict transepidermal water loss
Disadvantage - greasy - less cosmetically acceptable
What is a lotion?
Suspension or solution of medication in water, alcohol or other liquids
What areas do lotions treat?
Scalp and hair-bearing areas
Disadvantage of lotions
May sting if they contain alcohol
What is a gel?
Thickened aqueous solution. Semi-solid containing high molecular weight polymers
Which areas are gels used to treat?
Scalp, hair-bearing areas, face