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2ND YR DERM > Pharmacology > Flashcards

Pharmacology Flashcards

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Dermatology Board Prep flashcards
1
Q

benefits of using topical drug admin?

A

for local effect and to treat underlying tissue etc.

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2
Q

benefits of using transdermal/subcutaenous deposit admin?

A

good for prolonged systemic effects

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3
Q

name a few epithelial routes of drug admin other than topical or transdermal/subcutaenous

A
  • airways
  • bladder
  • conjunctival sac
  • nasal mucosa
  • rectum
  • vagina

all good for local effects that minimise systemic absorption

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4
Q

name the most important layer in skin for skin defence?

A

stratum corneum

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5
Q

what is the stratum corneum?

A
  • consists of layers of hard dead keratinocytes
  • forms 10-30 sheets of tissue that consistently shed
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6
Q

describe the brick and mortar model reference in the stratnum corneum

A
  • Bricks = corneocytes
  • Mortar = intercellular lipids in lamellar structures
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7
Q

what are corneocytes?

A

hardened dead keratinocytes

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8
Q

where is the stratnum corneum located in the epidermis?

A

outermost layer of the epidermis

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9
Q

where are the keratin filaments of the corneocytes embedded into?

A

embedded in filarggrin matris surrounded by a conrified cell envelope

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10
Q

what holds the corneocytes together?

A

corneo-desmosomes

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11
Q

what is the mortar in the stratnum conreum?

A
  • liquid layer
  • has multiple bilayers of lamellar intracellular lipids
  • can act as a resovoir for drugs
  • incredibly hydrophobic
  • liquid itself contains ceramides, cholesterol, free fatty acids etc.
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12
Q

what do drugs need for both local and systemic effects to work effectively?

A

be able to move through the stratnum corneum

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13
Q

how do most drugs move through the stratnum corneum?

A
  • via intercellular route
  • rely on molecules being small and hydrophobic
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14
Q

what law calculates how easily a drug is absorbed?

A

FIck’s law

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15
Q

Give the drug absorption equation

A

J (for john peters) = permability coefficient (K) X concetration of drug in medicine

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16
Q

what is the permeability coeffcient (K)?

A

basically involves what the drug is like and what the barrier contains

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17
Q

what is J in the drug absorption equation?

A

rate of absorption

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18
Q

give the rate of absorption equation

A
  • J = rate of absoprtion
  • Km = partition coefficient
  • D = diffusion coefficient
  • L = length of diffusion pathway
  • Cv = concentration of drug in the vehicle
19
Q

what is the best combination of frug solubility for absorption?

A
  • hydrophobic (lipophilic) drug in a hydrophilic base
  • best for absorption as it moves preferntially in to the skin
20
Q

what is the distribution of a hydrophobic (lipophilic) drug in a lipophilic base?

A
  • drug can move through the skin but will equal out between the skin and the blood vessels
21
Q

what occurs when you have a hydrophilic drug in a hydrophobic (lipophilic) base?

A

the two dont dissolve into eachother

  • so the drug partions only into the stratum corneum (weakly)
  • as the drug has limited solubility in both the vehicle AND the skin
22
Q

why is a lipophilic (hydrophobic) drug in a hydrophilic base beneficial?

A

drug is more soluble in the skin and preferentially partitions into it

23
Q

describe the solubility of a lipophilic (hydrophobic) drug in a lipophilic (hydrophobic) base?

A

drug is soluble in both vehicle (blood vessels) and skin so partitions between the two

24
Q

describe what happens to a hyrophilic drug in a hydrophilic base on the skin?

A
  • soluble in vehicle but not skin so remains on the surface of it
25
Q

why does a hydrophobic drug work so well in a hydrophilic base?

A

because a hydrophobic drug can make its way through the hyrophobic stratum corneum but wont bind to the base itself

26
Q

why are excipients added to drugs?

A

so the drug correctly dissolves into the liquid vehicle to make it through the skin

27
Q

give examples of vehicles for drugs?

A
  • lotions
  • creams
  • ointments
  • gels
  • pastes
  • powders
28
Q

what is the function of an excipient?

A
  • enhance the solubility of the drug in the vehicle
  • therefore enhance absorption
  • the excipients are compounds that will sit in patches and convert undissolved into soluble drug to move across skin
  • allow a constant drug flow to occur
29
Q

give an exmple of an excipient

A

propylene glycol

30
Q

what is the partiton coefficient?

A
  • concept for drugs to move in well they need to partition into the stratum conreum and enter the deeper layers of the skin
  • physical and chemical barriers of the skin help with this
31
Q

what is one factor that increases the partition coefficient?

A

Hydrated skin

  • allows hydrophilic base to settle into the skin better
  • can be done through addition of a good hydrating vehicle e.g. ointment
    • cling film will also help as it prevents water loss through exaporation
32
Q

how can increased partition be achieved by the skin itself?

A

reduction in the barrier function of the stratum corneum

33
Q

does location of application affect drug potency?

A

yes

  • e.g. steroid on sctorum will be far more potent than on the nail bed
34
Q

list some factors that may affect absorption of topically applied drugs?

A
  • hydration of skin
  • integrity of epidermis (moist/weeping vs. normal)
  • hair vs dry vs damages moist skin etc.
  • drug salt matters (some are more powerful than others)
  • some drugs more soluble in ointment than a cream (drug vehicle matters)
35
Q

what can long term use of high potency steroids result in?

A
  • steroid rebound
  • skin atrophy
  • systemic effects
  • spread of infection
  • steroid roasacea
  • production of stretch marks
  • superficial blood vessels
36
Q

what is transdermal drug delivery?

A
  • drugs penetrate through stratum corneum, epideris and dermis into systemic circulation
  • then delivered throughout the body to the site of action
37
Q

name the 4 features of a suitable drug for transdermal drug delivery?

A
  1. low molecular weight
  2. lipophilic/hydrophobic
  3. potent
  4. relatively brief half life
38
Q

give advantages of transdermal drug delivery

A
  • steady state of drug delivery
  • decreased dosing frequency
  • avoidance of first-pass metabolism
  • rapid termination of action
39
Q

disadvantages of transdermal drug delivery (TDD)?

A
  • relatively few drugs are suitable for this administration route
40
Q

give examples of TDD drugs?

A
  • nicotine
  • GTN
  • fnetanyl
  • oestradiol
41
Q

what can be incorporated into the TDD’s?

A
  • strain of chemicals that can be used to make the stratum conreum more permeable
  • makes it cheaper to administer some drugs
  • can be incorporated into TDD’s
  • can also be toxic for the skin and not effectuve for some soluble drugs
42
Q

why is the skin good for drug administration?

A
  • simple to apply
  • steady state plasma conc.
  • avoids first-pass metabolism
  • can be terminated rapidly because you can just wipe it off
43
Q

why is first-pass metabolism avoidance a good thing?

A

first-pass metabolism means that only a proportion of the drug reaches circulation due to it passing through portal vein into liver

2ND YR DERM (6 decks)

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