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Dermatology > Pharmacology > Flashcards

Pharmacology Flashcards

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Dermatology Board Prep flashcards
1
Q

Name the major routes of drug administration

A
  • topical; largely for local effect, but also to treat underlying issues (eg. topical NSAIDs)
  • transdermal
  • subcutaneous / depot
  • airways
  • conjunctival
  • nasal mucosa
  • vaginal
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2
Q

Name the single most important barrier to drug penetration into the skin, or diffusion across it

A

The stratum corneum

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3
Q

The stratum corneum consists of what?

A
  • hardened, dead, keratinocytes
  • surrounded by intercellular lipids formin 10 - 30 sheets of tissue (typically 20) that are constantly shed (desquamated) and renewed
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4
Q

The stratum corneum can be described as the brick and mortar model. Explain this

A
  • bricks; cornerocytes containing keratin microfilaments embedded in a filaggrin matrix surrounded by a cornified (protein) cell envelope. Corneocytes are highly cross linked by protein rivets (corneodesmosomes) providing tensile stength
  • mortar; multiple lamellar structures of intercellular lipids (mainly ceramides that link to corneocyte envelope, cholesterol, free fatty acid). A largely hydrophobic intercellular glue that can also act as a reservoir for lipid-soluble drugs (eg. topical glucocorticosteroids)
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5
Q

How is drug delivered across the stratum corneum?

A
  • via a passive process

- mediated by diffusion, when a drug is applied topically

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6
Q

Which conditions are treated topically for use for local effects?

A
  • superficial skin disorders (eg psoriasis, eczema)
  • skin infections (ie viral, bacterial, fungal and parasitic)
  • itching (pruritus)
  • dry skin
  • warts
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7
Q

The choice of vehicle for topical administration is dictated by what?

A
  • physiochemical properties of the drug

- the clinical condition

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8
Q

Which drugs contain the most water and which contain the least?

A

Most to least

  • lotions
  • creams
  • ointments
  • gels
  • pastes
  • powders
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9
Q

The vehicle (or base) can profoundly affect rate and extent of absorption of a topically applied drug. Name some important factors

A
  • dissolved concentration of the drug in vehicle (Cv)

- the movement (or partitioning) of the drug from vehicle into the stratum corneum and deeper (Km)

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10
Q

Lipophilic drug in lipophilic base is soluble where?

A
  • soluble in both vehicle and skin and partitions between the two
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11
Q

Lipophilic drug in hydrophobic base is soluble where?

A

Most soluble in the skin and preferentially partitions into it

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12
Q

Hydrophilic drug in lipophilic base is soluble where?

A
  • has limited solubility in both vehicle and skin and partitions into it weakly
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13
Q

Hydrophilic drug in hydrophilic base is soluble where?

A
  • soluble in vehicle but not skin and remains on the surface
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14
Q

For drugs applies topically, what provides the driving force for skin penetration

A
  • the fraction within the vehicle solubilised (Cv), not that undissolved
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15
Q

Inclusion of what within the vehicle can enhance drug solubility and enhance absorption?

A

Excipients (eg. propylene glcyol)

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16
Q

Are topically applied drugs well or poorly absorbed?

A

Poorly - only a small fraction partitions into the skin

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17
Q

Name some physical and chemical factors that can improve partitioning

A
  • hydration of the skin by occlusion (prevention of water loss by evaporation)
  • may be achieved by choice of vehicle (eg. ointment versus oil in water cream)
  • cling film
  • inclusion of excipients that also increase the solubility of hydrophobic drugs
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18
Q

Increased partitioning results from what?

A

A reduction in the barrier function of the stratum corneum

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19
Q

Describe the nature of the skin as a factor that influences absorption topically

A
  • site of application (thickness of stratum corneum / skin)
  • hydration of the skin (vehicles and occlusive dressings)
  • integrity of the epidermis (absorption influenced by trauma, inflammation/ other disease processes)
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20
Q

Describe drug / pharmaceutical preparation as a factor influencing absorption topically

A
  • drug concentration and properties
  • the drug salt
  • the vehicle (betamethasone valerate more active as an ointment than as a cream, or lotion)
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21
Q

Describe the features of glucocorticoids

A
  • widely used topically in the treatment of atopic eczema, psoriasis and pruritus
  • posses anti-inflammatory, immunosuppressant and vasoconstricting effects plus anti-proliferating action upon keratinocytes and fibroblasts
  • available in several formulations
  • adverse events less likely with topical application, but system adverse events can occur
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22
Q

Penetration, potency and clinical effect varies with what?

A
  • body site; eg thickness of stratum corneum
  • state of the skin; eg infants and children have thin skin that is more permeable to glucocorticoids
  • occlusion
  • specific drug and its concentration
  • vehicle; affects potency, affects compliance
  • formulation of drug; 1% hydrocortisone acetate is mild but 0.1% hydrocortisone butyrate is potent
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23
Q

Name some serious adverse effect of long term use of higher potency steroids

A
  • steroid rebound (glucocorticoid receptor down-regulation)
  • skin atrophy (that may not be totally reversible)
  • systemic effects (HPA axis depression due to systemic absorption)
  • spread of infection (due to immune suppression in the skin)
  • steroid rosacea (skin reddening and pimples of facial skin)
  • production of stretch marks (striae atrophica) and small superficial dilated blood vessels (telangiectasia)
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24
Q

True or flase?

Glucocorticoids are lipophilic molecules

A

True

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25
Q

Within the cytoplasm, glucocorticoids combine with what?

A
  • GRalpha producing dissociation of inhibitory heat shock proteins (eg. HSP90)
  • the activated receptor translocated to the nucleus aided by importins
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26
Q

Describe the action of glucocorticoids within the nucleus

A
  • activated receptor monomers assemble to homodimers and bind to glucocorticoid response elements (GRE) in the promotor region of the specific genes
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27
Q

How does the drug reach the systemic circulation when administered subcutaneously?

A
  • diffusion into either capillaries or lymphatic vessels (particularly high molecular weight compounds)
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28
Q

Describe the advantages of the subcutaneous route of administration

A
  • absorption is relatively low due to poor vascular supply
  • route for administration for many protein drugs (eg insulin) and suitable for administration of oil based drugs (eg steroids)
  • can be used to introduce a depot of drug under the skin that is very slowly released into the circulation
  • relatively simple and fairly painless
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29
Q

Describe the disadvantages of the subcutaneous route of administration

A
  • injection volume limited
30
Q

Why is the skin an attractive route of drug administration for a systemic effect?

A
  • application is simple and non-sterile (when drug is applied topically
  • potentially allows for a steady state plasma concentration of drug to be achieved over a prolonged period of time
  • avoids first pass metabolism, for example by the intestine and liver and potential toxicity to those organs
  • drug absorption can be terminated rapidly (with the caveat that some drug may have accumulated in the skin)
31
Q

What is a disadvantage of the skin as a route of drug administration?

A
  • intact skin is a water tight barrier
  • only a limited number of drugs diffuse across the epidermis to reach the superficial capillaries of the dermis to be systemically available at an effective concentration
32
Q

Describe transdermal drug delivery

A
  • drug absorption is partially controlled by a drug release membrane - occurs by diffusion across cutaneous barrier
  • most suitable for drugs that are low molecular weight, moderately lipophilic, potent or have a relatively brief half-life
33
Q

Describe advantages of transdermal drug delivery

A
  • steady state of drug delivery, decreased dosing frequency, avoidance of first pass metabolism, rapid termination of action ( if t1/2 is short)
  • user friendly, convenient, painless, increased patient concordance
34
Q

Describe disadvantages of transdermal drug delivery

A
  • relatively few drugs suitable for TDD (although increasing)
  • allergies
  • cost
35
Q

Name some drug examples of transdermal drug delivery

A
  • scopolamine
  • nicotine
  • GTN
  • fentanyl
  • buprenorphine
  • estradiol
36
Q

Describe the chemical enhancement of transdermal drug delivery

A
  • enhancers interact with the lipid matrix of the stratum corneum to increase permeability, mianly to drugs that already cross the skin reasonably well
37
Q

Name some agents that chemically enhance transdermal drug delivery

A
  • water; prolonged occlusion (via topical formulation or patch, causes increased hydration of the stratum corneum and the formation of a pore pathway
  • a variety of solvents (eg ethanol) and surfactants (eg sodium dodecyl sulphate)
38
Q

Describe the advantages of topical treatments

A
  • direct application

- reduced systemic effects

39
Q

Describe the disadvantages of topical treatments

A
  • time consuming
  • correct dosage can be difficult
  • messy to use
40
Q

Drugs used on the skin are dissolved in bases or vehicles, name some

A
  • gels
  • creams
  • ointments
  • pastes
  • lotions
  • foams
41
Q

Describe creams

A
  • semisolid emulsion of oil in water
  • contain emulsifier and preservative (to increase shelf life)
  • high water content (to help with cooling)
  • cool and moisturise
  • non greasy
  • easy to apply
  • cosmetically acceptable
42
Q

Describe ointments

A
  • semisolid grease/oil
  • no preservative
  • occlusive and emollient
  • restrict transepidermal water loss
  • greasy; less cosmetically attractive
  • no sharing of ointment to avoid bacterial infection due to no preservative
43
Q

Describe lotions

A
  • liquid formulation
  • suspension or solution of medication in water, alcohol or other liquids
  • if contain alcohol, may sting
  • treat scalp, hair bearing areas
44
Q

Describe gels

A
  • thickened aqueous lotions
  • semisolids, containing high molecular weight polymers eg methylcellulose
  • treat scalp, hair bearing areas, face
45
Q

Describe pastes

A
  • semisolids
  • contain finely powdered material eg ZNO
  • stiff, greasy, difficult to apply
  • protective, occlusive, hydrating
  • often used in cooling, drying, soothing bandages
46
Q

Describe foams

A
  • colloid with two-three phases
  • usually hydrophilic liquid in continuous phase with foaming agent dispersed in gaseous phase
  • advantage of increased penetration of active agents (eg steroid, vitamin D)
  • advantage that can spread easily over large areas of skin, no greasy / oily film
47
Q

What form of treatment would you give for icthyosis?

A

Lotion

48
Q

What form of treatment would you give child hand dermatitis?

A

Cream

49
Q

What form of treatment would you give scalp psoriasis?

A

Gel

50
Q

What form of treatment would you give hyperkeratotic hand eczema?

A

Ointment

51
Q

Name some types of topical therapies

A
  • emollients
  • topical steroids
  • anti-infective agents; antiseptics, antibiotics, antivirals, antifungals
  • antipruritics
  • keratolytics
  • psoriasis therapies
  • cytotoxic and antineoplastic agents
52
Q

Describe emollients

A
  • enhance rehydration of epidermis
  • for all dry/scaly conditions especially eczema
  • need to be effective and cosmetically acceptable
  • prescribe 300-500g
  • needs frequent application
53
Q

Describe the prescribing tips for emollient

A
  • apply immediately after bathing
  • apply in direction of hair growth (can block hair follicles and cause infection)
  • make skin and surfaces slippery
  • use clean spoon or spatula to remove from tub
  • fire risk if paraffin based
  • avoid these containing SLS in leave on products
54
Q

What is wet wrap therapy used for?

A

Very dry (xerotic) skin

55
Q

What is the mode of action for topical corticosteroids?

A
  • vasoconstrictive
  • anti inflammatory
  • antiproliferative
56
Q

Name topical steroids in order of mild to high potency

A
  • mild; hydrocortisone 1%
  • moderate; modrasone, clobetasone butyrate 0.05%
  • potent; mometasone, betamethasone valerate 0.1%
  • very potent; clobestaol proprionate 0.05%
57
Q

Name some uses for topical corticosteroids

A
  • eczema (dermatitis)
  • psoriasis (eg flexures, face, hairline, scalp) beware round, triggering pustular psoriasis
  • other non-infective inflammatory dermatoses eg lichen planus
  • keloid scars (intralesional or tape)
58
Q

Describe calicneurin inhibitors

A
  • tacrolimus, pimecrolimus
  • suppress lymphocyte activation
  • topical treatment of atopic eczema (esp. face, children)
  • no cutaneous atrophy
  • may cause burning sensation on application
59
Q

What are the four types of antiinfectives?

A
  • antiseptics
  • antibiotics
  • antivirals
  • antifungals
60
Q

Name some examples of antiseptics and their function

A
  • have bacteriostatic or bactericidal effects
  • povidone iodine skin cleanser
  • chlorhexidine (hibitane, savlon)
  • triclosan (aquasept, sterzac)
  • hydrogen peroxide (crystacide)
61
Q

Describe the clinical uses of antiseptics

A
  • recurrent infections (broad spectrum)
  • skin cleansing
  • wound irrigation
62
Q

Describe some clinical uses of antibiotics

A
  • treatment of acne and rosacea
  • treatment of skin infection eg impetigo
  • treatment of infected eczematous process eg otitis externa
63
Q

Name some topical antifungals

A
  • candida; antiyeast eg nystatin, clotrimazole
  • dermatophytes; antifungal eg clotrimazole, terbinafine cream
  • pityriasis versicolor; ketoconazole (cream or shampoo)
64
Q

Name some antipruritics

A
  • menthol; added to calamine and other lotions and creams to impart cooling sensation
  • capsaicin; depletes substance P at nerve endings and reduced neurotransmission, effect gradually builds
  • camphor / phenol; for pruritus ani
  • crotamiton; eg eurax cream, used after treatment of scabies to relieve residual itch
65
Q

What are keratolytics used for?

A
  • to soften keratin
  • viral warts
  • hyperkeratotic eczema and psoriasis
  • corns and calluses
  • to remove keratin plaques in scalp
66
Q

Describe the treatment of warts

A
  • mechanical paring plus
  • keratolytics eg salicyclic acid
  • formaldehyde
  • glutaraldehyde
  • silver nitrate
  • cryotherapy (usually liquid nitrogen)
  • podophyllin (genital warts)
67
Q

Describe some topical psoriasis treatments

A
  • emollients and choice of;
  • coal tar
  • vitamin D analogue
  • keratolytic
  • topical steroid
  • dithranol
  • based on; sites affected, extent, severity, side effects, compliance
68
Q

Describe coal tar

A
  • mild solutions to strong crude coal tar

- messy and smelly

69
Q

Describe vitamin D analogues

A
  • clean, no smell
  • easy to apply
  • can be an irritant
  • use limited to 100g weekly
70
Q

Describe dithranol

A
  • effective
  • difficult to use
  • irritant and stains normal skin
71
Q

Describe treatment for scalp psoriasis

A
  • greasy ointments to soften scale
  • tar shampoo
  • steroids in alcohol base or shampoo
  • vitamin d analogues
72
Q

Describe cytotoxic and antineoplastic therapies

A
  • 5 fluorouracil for solar damage, bowens disease and superficial basal cell carcinoma
  • imiquimod for solar damage and superficial basal cell carcinoma

Dermatology (10 decks)

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