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DERMATOLOGY > Pharmacology > Flashcards

Pharmacology Flashcards

1
Q

What is unusual about the factors considered in the case of drugs applied to the skin?

A

The vehicle in which the drug is solubilized/delivered is almost as important as the choice of drug itself in producing the desired therapeutic effect

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2
Q

What are the major routes of drug administration associated with the skin?

A
  1. Topical
  2. Transdermal
  3. SC
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3
Q

What route is used for local affect?

A

Topical

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4
Q

What route is used for system effect?

A

Transdermal OR SC

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5
Q

Other than skin routes, give examples of other epithelial routes of drug administration.

A
  • Airway
  • Bladder
  • Conjunctival
  • Nasal
  • Rectum
  • Vagina
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6
Q

What is the major advantage of administering drugs via epithelial routes?

A

All of these routes allow a relatively high local concentration of drug, but minimise adverse systemic effects – a major advantage of topical administration when intended for LOCAL effect.

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7
Q

What is the single most important barrier for drug penetration?

A

Stratum corneum

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8
Q

Describe the structure of the stratum corneum.

A

Consists of corneocytes (hardened, dead, keratinocytes) surrounded by intercellular lipids forming 10 - 30 sheets of tissue (typically 20) that are constantly shed (desquamated) and renewed

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9
Q

Name the layers of the epidermis (from outer to inner).

A
  1. Keratin
  2. Granular
  3. Prickle
  4. Basal
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10
Q

Describe the ‘brick and mortar’ model of the stratum corneum.

A

Bricks - corneocytes

Mortar - multiple bilayers of lamellar structures of intercellular lipids

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11
Q

What are corneocytes held together by?

A

Corneodesmosomes

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12
Q

What are corneocytes embedded in?

A

Fillagrin

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13
Q

What do corneocytes contain?

A

Keratin

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14
Q

The stratum corneum is highly ___________ and can act as a reservoir for _____ _______ drugs

A

i) Hydrophobic

ii) Lipid soluble drugs

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15
Q

Both local and systemic effects of drugs require penetration of what? How does this largely occur?

A

The stratum corneum.

Via the intercellular route, and normally allows only diffusion of small, hydrophobic drugs.

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16
Q

What does the ‘topical’ route of administration refer to?

A

A drug – in a pharmacologically inactive substance, or vehicle – being applied directly onto the surface of the skin

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17
Q

Vehicles are usually ________

A

INACTIVE

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18
Q

Give examples of vehicles used in the topical route of administration

A

Ointments, creams, gels, lotions, pastes, powders

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19
Q

What is the choice of vehicle dictated by?

A
  1. Physiochemical properties of the drug
  2. The clinical condition ie. If skin is moist and weeping, don’t use ointment, but do use ointment if the skin is very dry.
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20
Q

What type of process is conventional transdermal drug delivery, and what is this driven by?

A

A passive process, driven by diffusion

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21
Q

What is rate of drug absorption/rate at which the drug crosses the barrier also known as?

A

Flux, J

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22
Q

What increases flux/rate of absorption?

A
  • An increase in Km, the partition coefficient.
  • An increase in D, the diffusion coefficient.
  • An increase in Cv, the concentration of drug in the vehicle.
  • A decrease in L, the length of the diffusion pathway.
23
Q

Why is the choice of vehicle so important?

A

The vehicle can profoundly influence the rate and extent of absorption of a topically applied drug

24
Q

When choosing a vehicle, what 2 factors should you consider?

A
  • Solubility of the drug in the vehicle

* Maximising the separation from the drug from the vehicle at stratum corneum

25
Q

What is Km described as?

A

The solubility of the drug in the stratum corneum (sc) relative to its solubility in the vehicle:
Km = Csc/Cv. This is the partition coefficient

26
Q

What is Km described as?

A

The solubility of the drug in the stratum corneum (sc) relative to its solubility in the vehicle:

Km = Csc/Cv. This is the partition coefficient

27
Q

What drug type does not pass the stratum corneum readily?

A

HYDROPHILIC

28
Q

Name the best drug type and vehicle type for absorption.

A

Lipophilic drug in a hydrophilic base

29
Q

When drugs are applied topically only what fraction provides the driving force for absorption?

A

The soluble fraction

30
Q

The inclusion of what in the vehicle can enhance solubility and enhance absorption?
Give an example.

A

Excipients

eg. Propylene glycol can be added, enhancing the solubility of glucocorticoids

31
Q

What is the advantage of having excess, non-dissolved, drug included in transdermal patches?

A

This can increase the duration of effectiveness and provide a constant rate of delivery – dissolved drug that is removed by absorption is replaced by undissolved drug, maintaining a fairly constant soluble concentration

32
Q

Why are topically applied drugs generally poorly absorbed?

A

Only a small fraction portions into the stratum corneum

33
Q

Outline physical and chemical factors which can improve partitioning

A
  • Hydration of the skin
  • Choice of vehicle
  • Cling film
  • Excipients
34
Q

What does a reduction in the barrier function of the stratum corneum result in? Why may this be the case?

A

Increased partitioning

Due to the reversible development of the pore pathway

35
Q

Stratum corneum is thicker or thinner in different parts of the body, outline this in order of thickest to thinnest

A
  1. palm/sole
  2. trunk/extremities
  3. face/scalp
  4. scrotum
36
Q

Hydrocortisone butyrate is far more potent than hydrocortisone acetate, why?

A

TRUE
Butyrate is far more hydrophobic
Acetate is hydrophilic

37
Q

What are glucocorticoids mostly used in the treatment of?

A

Atopic eczema

38
Q

Describe the effect of glucocorticoids.

A
  • Anti-inflammatory
  • Immunosuppressant
  • Vasoconstricting

Also anti-proliferating action upon keratinocytes and fibroblasts

39
Q

Outline the factors with which glucocorticoid penetration, potency and clinical effect vary with

A
  • Body site
  • State of the skin
  • Occlusion
  • Vehicle
  • Concentration of drug
  • Form of the drug
40
Q

Glucocorticoids are __________ and enter cells by _________ across the ______ ________

A

i) lipophilic
ii) diffusion
iii) plasma membrane

41
Q

How does a drug delivered SC reach the circulation?

A

Via capillaries

42
Q

Describe the absorption of a drug given SC.

A

Slow - due to poor vascular supply in adipose tissue

43
Q

Why is the skin good as a route for systemic drug administration?

A
  • Sterile
  • Steady state plasma conc achieved over a long time
  • Avoids first pass metabolism
  • Drug absorption can be terminated rapidly
44
Q

What is the main disadvantage of using the skin as a route of drug administration for a systemic effect?

A

Skin is a water-tight barrier (if intact)

45
Q

Describe transdermal drug delivery.

A

Drug put into an adhesive patch and applied to the dermis

46
Q

What type of drug can be given via TDD?

A
  • LMW
  • Lipophilic
  • Potent/brief half life
47
Q

Give examples of drugs administered transdermally.

A

Nincotine
GTN
Fentanyl
Estradiol

48
Q

Give advantages of administering a drug transdermally.

A

Steady rate of drug delivery,
Decreased dosing frequency,
Avoidance of first-pass metabolism,
Rapid termination of action (if t½ is short)

49
Q

What can be used to enhance TDD?

A

Chemical enhancers

50
Q

How do chemical enhancers work?

A

Enhancers interact with the lipid matrix of the stratum corneum to increase permeability, mainly to drugs that already cross the skin reasonably well

51
Q

Give an example of an agent which enhances TDD.

A

Water – PROLONGED OCCLUSION

52
Q

Name 4 strategies that are used to physically enhance transdermal drug delivery.

A
  • Iontophoresis
  • Electroporation
  • Sonophoresis
  • Microneedles
53
Q

If you want to know more about strategies to enhance TDD….

A

Look at notes

DERMATOLOGY (6 decks)

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