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Flashcards in Pharmacology Deck (22)
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1
Q

What are the main routes of drug administration in the skin?

A

Topical
Transdermal
Subcutaneous

2
Q

Other than the skin, what other epithelial routes can be used for drug administration?

A
Airways 
Bladder
Conjunctival sac 
Nasal mucosa
Rectum
Vagina
3
Q

What is the single most important barrier to drug penetration?

A

The stratum corneum (keratin layer)

4
Q

What makes up the stratum corneum?

A

corneocytes (hardened, dead, keratinocytes)

surrounded by intercellular lipids forming 10 - 30 sheets of tissue (these are constantly shed and renewed)

5
Q

What are the two routes by which drugs can travel through the stratum corneum?

A

Transcellular

Intercellular

6
Q

What holds adjacent corneocytes together?

A

corneodesmosomes

7
Q

describe the structure of the intercellular route

A

multiple bilayers of lamellar structures of intercellular lipids

Highly hydrophobic and can act as a reservoir for lipid-soluble drugs (e.g. topical corticosteroids)

8
Q

In what conditions are topical agents most likely to be used?

A
superficial skin disorders 
skin infections
itching (pruritus) 
dry skin 
warts
9
Q

What formula describes the factors which influence absorption of a topical drug?

A

Fick’s Law of Diffusion

                                 J = KpCv
J = Rate of absorption 
Kp = permeability coefficient 
Cv = concentration of drug in the topical medication
10
Q

What part of topical drugs provides the driving force for absorption?

A

soluble fraction

11
Q

What substances can be added to topical drugs to aid solubility?

A

excipients (e.g. propylene glycol)

12
Q

What factors can affect the absorption of topical drugs?

A
  • Site of application (thickness of stratum corneum)
  • hydration of the skin
  • Integrity of the epidermis
  • drug concentration / physicochemical properties
  • drug salt (hydrocortisone butyrate far more potent than hydrocortisone acetate)
  • vehicle (betamethasone valerate more active as an ointment than as a cream, or lotion)
13
Q

How are subcutaneous drugs delivered to the body?

A

needle inserted into the fatty (adipose) tissue just beneath the surface of the skin

Drug reaches systemic circulation by diffusion into either:

  • capillaries
  • lymphatic vessels (particularly high molecular weight compounds)
14
Q

What are the advantages of subcutaneous drugs?

A

Absorption = slow

Relatively simple and painless

Route of administration for many protein drugs (e.g. insulin)

Suitable for administration of oil-based drugs (e.g. steroids)

Used to introduce depot of drug under skin that is slowly released into the circulation:

  • certain contraceptive steroids (medroxyprogesterone)
  • antipsychotic drugs (fluphenazine decanoate)
15
Q

What disadvantage do subcutaneous drugs have?

A

Injection volume is limited

16
Q

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

A

Application = simple and non-sterile

Allows steady-state plasma concentration (Cpss) of drug to be achieved over a prolonged period of time

Avoids first pass metabolism

Drug absorption can be terminated rapidly

17
Q

What drugs are most suitable for transdermal delivery?

A

(i) low molecular weight
(ii) moderately lipophilic
(iii) potent
(iv) of relatively brief half-life (t½)

18
Q

What are the advantages of transdermal drug delivery?

A
  • Steady rate of drug delivery
  • decreased dosing frequency,
  • avoidance of first-pass metabolism
  • rapid termination of action (if t½ is short)
  • User friendly, convenient, painless
19
Q

What are the disadvantages of transdermal drug delivery?

A
  • Relatively few drugs suitable
  • allergies
  • cost
20
Q

Give examples of drugs that can be administered transdermally?

A

nicotine
GTN
Fentanyl
estradiol

21
Q

What do chemical enhancers do to improve transdermal drug delivery?

A

interact with the lipid matrix of the stratum corneum to increase permeability

(mainly to drugs that already cross the skin reasonably well)

22
Q

What agents can be used to chemically enhance a transdermal patch?

A

Water – increased hydration of the stratum corneum and the formation of a ‘pore’ pathway

Variety of solvents (e.g. ethanol) and surfactants (e.g. sodium dodecyl sulphate)