Topical Preparations

Question 1

Describe topical

Answer 1

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

Question 2

Why do it minimise systemic?

Answer 2

To minimise side effects

Question 3

How is it different to transdermal?

Answer 3

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

Question 4

What are advantages?

Answer 4

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

Question 5

What are disadvantages?

Answer 5

Low skin permeability
Skin irritation
Difficult to determine dose

Question 6

What is problem with low skin permeability?

Answer 6

Only small section of drugs deliverable + uptake slow

Question 7

Describe ointment

Answer 7

Drug dissolved or dispersed in greasy base

Occlusive

Question 8

What are disadvantages of ointment?

Answer 8

Difficult to spread

Patient acceptability could be low

Question 9

Why is ointment occlusive?

Answer 9

Promotes skin hydration by minimising trans epidermal H2O loss

Question 10

Describe cream

Answer 10

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

Question 11

What are advantages of cream?

Answer 11

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

Question 12

Describe gel

Answer 12

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

Question 13

What disadvantage of gel?

Answer 13

May form occlusive film on skin when dried

Question 14

Describe lotion

Answer 14

H2O based = non-occlusive

Solution, suspension or emulsion

Question 15

What is lotion used for?

Answer 15

Cleaning or disinfection

Question 16

What are advantages of lotion?

Answer 16

Highly spreadable

Suitable for hairy skin

Question 17

Why is it good it is highly spreadable?

Answer 17

Ideal for covering large area thinly

Question 18

What is the problem of lotion?

Answer 18

Short residence time

Question 19

How to fix short residence time of lotion?

Answer 19

Increase viscosity

Question 20

Describe foam

Answer 20

Dispersion of gas within liquid

Drug dissolved in liquid phase

Question 21

What is foam available in?

Answer 21

Pressurised cans

Question 22

How does foam work?

Answer 22

Generated during use + stable only momentarily

Question 23

Describe spray

Answer 23

Aerosol = dispersion of liquid droplets in gas

Fine mist generated using propellant in pressurised can

Question 24

What is advantage of spray?

Answer 24

Administration without direct skin contact

Rapid + even coverage of large SA

Question 25

Describe patch

Answer 25

Similar to trans dermal BUT for topical delivery | Solid dosage form containing drug on adhesive film

Question 26

What are advantages of patch?

Answer 26

Discrete dosage unit = enables accurate dosage | Provides occlusion, dose retention + protection of formulation

Question 27

What are the dermal drug transport mechanism?

Answer 27

Partitioning | Diffusion

Question 28

Describe partitioning

Answer 28

From one medium into another, solubility-driven

Question 29

Describe diffusion

Answer 29

Within same medium, down conc gradient

Question 30

What is skin permeability?

Answer 30

Function of partitioning coefficient + diffusion coefficient

Question 31

How do you calculate permeability coefficient?

Answer 31

Kp = KD/ h ``` Kp = permeability coefficient K = partition coefficient D = diffusion coefficient h = Diffusion pathway length ```

Question 32

What is the transcellular route?

Answer 32

Straight through corneocyte = hydrophilic drug

Question 33

What is paracellular route?

Answer 33

Around corneocyte through lipids = lipophilic drug

Question 34

What is the shunt pathway?

Answer 34

Through hair follicles + sebaceous glands

Question 35

Why is the shunt pathway important?

Answer 35

For innovative drug delivery strategies

Question 36

Why is the shunt pathway traditionally regarded as negligible?

Answer 36

Small skin area

Question 37

What factors affect dermal drug transport? | Drug properties

Answer 37

``` Lipophilicity (logP 1-4) Molecular weight (<5000) ```

Question 38

What factors affect dermal drug transport? | Anatomical site

Answer 38

Barrier thickness | Hair follicle density

Question 39

What factors that affect dermal drug absorption?

Answer 39

Age | Disease

Question 40

Why is age a factor that affect dermal drug absorption?

Answer 40

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

Question 41

Why is disease a factor that affect dermal drug absorption?

Answer 41

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

Question 42

What do you asses with in vivo dermal drug transport?

Answer 42

Ethical considerations Clinical support Suitability of animal method

Question 43

What do you asses with in vitro dermal drug transport?

Answer 43

Ethical considerations | Suitability of skin model

Question 44

How is drug lost from applied dose?

Answer 44

Remaining dose on administration site

Question 45

Describe microdialysis

Answer 45

Semi-permeable tube inserted surgically below skin | Permeated drug collected in perfusate

Question 46

Describe tape stripping

Answer 46

Stratum corneum progressively removed by adhesive tape | Drug assayed relative to protein content of strip

Question 47

What must be assumed in tape stripping?

Answer 47

Each strip removes materials from single cellular layer

Question 48

What is a problem with tape stripping?

Answer 48

Tape constituents may contaminate sample

Question 49

What is the problem with microdialysis?

Answer 49

Invasive

Question 50

What are the three types of diffusion cells?

Answer 50

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

Question 51

Describe what happens in diffusion cell

Answer 51

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

Question 52

What is the mass balance? | Diffusion cell

Answer 52

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