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Pharmaceutics > Topical Preparations > Flashcards

Topical Preparations Flashcards

1
Q

Describe topical

A

Administered on tissue surface
Local condition
Site administration is site of therapeutic action
Commonly skin

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2
Q

Why do it minimise systemic?

A

To minimise side effects

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3
Q

How is it different to transdermal?

A

Administered on skin surface
Act at remote site away from site administration
Requires systemic drug absorption

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4
Q

What are advantages?

A 
Avoid GI + 1st-pass 
Non-invasive
Patient compliance
Better drug targeting = minimal systemic side effects
Easy dose withdrawal
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5
Q

What are disadvantages?

A

Low skin permeability
Skin irritation
Difficult to determine dose

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6
Q

What is problem with low skin permeability?

A

Only small section of drugs deliverable + uptake slow

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7
Q

Describe ointment

A

Drug dissolved or dispersed in greasy base

Occlusive

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8
Q

What are disadvantages of ointment?

A

Difficult to spread

Patient acceptability could be low

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9
Q

Why is ointment occlusive?

A

Promotes skin hydration by minimising trans epidermal H2O loss

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10
Q

Describe cream

A

Semi-solid emulsion
Multiphase dispersion of O/W or W/O
Longer residence time than lotion

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11
Q

What are advantages of cream?

A

Mixable with skin secretions, easily washable
Excellent patient acceptability
Less greasy than ointment

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12
Q

Describe gel

A

Semi-solid, often clear
Polymer network interpenetrated by liquid
Mostly aq
Drug dissolved in liquid component

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13
Q

What disadvantage of gel?

A

May form occlusive film on skin when dried

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14
Q

Describe lotion

A

H2O based = non-occlusive

Solution, suspension or emulsion

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15
Q

What is lotion used for?

A

Cleaning or disinfection

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16
Q

What are advantages of lotion?

A

Highly spreadable

Suitable for hairy skin

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17
Q

Why is it good it is highly spreadable?

A

Ideal for covering large area thinly

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18
Q

What is the problem of lotion?

A

Short residence time

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19
Q

How to fix short residence time of lotion?

A

Increase viscosity

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20
Q

Describe foam

A

Dispersion of gas within liquid

Drug dissolved in liquid phase

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21
Q

What is foam available in?

A

Pressurised cans

22
Q

How does foam work?

A

Generated during use + stable only momentarily

23
Q

Describe spray

A

Aerosol = dispersion of liquid droplets in gas

Fine mist generated using propellant in pressurised can

24
Q

What is advantage of spray?

A

Administration without direct skin contact

Rapid + even coverage of large SA

25
Q

Describe patch

A

Similar to trans dermal BUT for topical delivery

Solid dosage form containing drug on adhesive film

26
Q

What are advantages of patch?

A

Discrete dosage unit = enables accurate dosage

Provides occlusion, dose retention + protection of formulation

27
Q

What are the dermal drug transport mechanism?

A

Partitioning

Diffusion

28
Q

Describe partitioning

A

From one medium into another, solubility-driven

29
Q

Describe diffusion

A

Within same medium, down conc gradient

30
Q

What is skin permeability?

A

Function of partitioning coefficient + diffusion coefficient

31
Q

How do you calculate permeability coefficient?

A

Kp = KD/ h

Kp = permeability coefficient 
K = partition coefficient
D = diffusion coefficient
h = Diffusion pathway length
32
Q

What is the transcellular route?

A

Straight through corneocyte = hydrophilic drug

33
Q

What is paracellular route?

A

Around corneocyte through lipids = lipophilic drug

34
Q

What is the shunt pathway?

A

Through hair follicles + sebaceous glands

35
Q

Why is the shunt pathway important?

A

For innovative drug delivery strategies

36
Q

Why is the shunt pathway traditionally regarded as negligible?

A

Small skin area

37
Q

What factors affect dermal drug transport?

Drug properties

A 
Lipophilicity (logP 1-4)
Molecular weight (<5000)
38
Q

What factors affect dermal drug transport?

Anatomical site

A

Barrier thickness

Hair follicle density

39
Q

What factors that affect dermal drug absorption?

A

Age

Disease

40
Q

Why is age a factor that affect dermal drug absorption?

A

Thickness, hydration, lipid content + microvascular clearance decline with age
Corneocytes enlarge with age

41
Q

Why is disease a factor that affect dermal drug absorption?

A 
Broken skin = highly permeable
Scaly skin (peeling) = impaired permeability barrier BUT also dehydrated = reduce permeability
Thick skin = reduced permeability = increased diffusion pathway length
42
Q

What do you asses with in vivo dermal drug transport?

A

Ethical considerations
Clinical support
Suitability of animal method

43
Q

What do you asses with in vitro dermal drug transport?

A

Ethical considerations

Suitability of skin model

44
Q

How is drug lost from applied dose?

A

Remaining dose on administration site

45
Q

Describe microdialysis

A

Semi-permeable tube inserted surgically below skin

Permeated drug collected in perfusate

46
Q

Describe tape stripping

A

Stratum corneum progressively removed by adhesive tape

Drug assayed relative to protein content of strip

47
Q

What must be assumed in tape stripping?

A

Each strip removes materials from single cellular layer

48
Q

What is a problem with tape stripping?

A

Tape constituents may contaminate sample

49
Q

What is the problem with microdialysis?

A

Invasive

50
Q

What are the three types of diffusion cells?

A

Franz-type vertical
Side-by-side
Flow-through

51
Q

Describe what happens in diffusion cell

A

Skin sandwiched between donor + receptor channels
Stratum corneum facing donor chamber
Drug formulations administered into donor chamber
Receptor chamber filled with receptor buffer
Drug can only pass through skin to receptor chamber
Drug sampled from receptor + assayed

52
Q

What is the mass balance?

Diffusion cell

A

Drug recovered from donor chamber + drug extracted from skin + drug assayed in donor receptor + 100% dose

Pharmaceutics (21 decks)

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