Skin Content

Question 1

Give a drug that was once used for oral route but changed into topical delivery

Answer 1

Rivastigmine

Question 2

What are the two properties with relative ease of permeation in skin

Answer 2

1. Lipophilic molecules are delivered better compared to hydrophilic
2. Lower melting point is better absorbed

Question 3

What are the pharmacokinetic properties an ideal topical drug should have

Answer 3

1. Molecular weight: 300 - 500
2. Log P: 1-3.5
3. Aqueous solubility: >100mg/mL

Question 4

How do you estimate drug flux

Answer 4

Using mathematical models of empirical relationships between flux, log P, solubility and molecular weight

Works alright for mid range molecules and small moderately lipophilic molecules

Question 5

What are the different phases of liquid formulation and its advantages

Answer 5

1. Allows rapid short term drug input into skin
2. Single phase: non polar solution (oils) example: liquid paraffin
3. Two phase: Dilute emulsions (o/w and w/o) found in lotions
4. Multi phase: Dilute multiple emulsions (o/w/o or w/o/w)

Question 6

What are the different phases of semisolid formulation and its advantages

Answer 6

1. Has increased residency time on sin
2. Single phase: ointment (dissolved medicaments)
3. Two phase: Emulsions (o/w or w/o) dispersed medicament that include creams
4. Multi phase: Multiple emulsions with dispersed medicaments (cream pastes)

Question 7

What are the different phases of solid formulation and its advantages

Answer 7

1. Extended drug delivery via skin
2. Single phase: Powders
3. Two phase: Transdermal patches (some)
4. Multi phase: Complex transdermal patches

Question 8

What are the different skin types and what formulation of topical delivery should you use on them?

Answer 8

1. Normal to oily: Gels
2. Normal to dry: Lotions
3. Dry skin: creams
4. Hairy: lotions, gels, sprays
5. Intertriginous areas: rubbing of two skins (arm pit): creams or lotions

Question 9

How do you treat a wet, vesicular or weeping lesion

Answer 9

Using creams, lotions or gels

Hydrophilic drugs: aqueous system water, co solvents of propylene glycol and avoiding alcohols

Hydrophobic drugs: mineral oils

Question 10

How do you treat a dry, thickened scaly leision

Answer 10

Fatty formulation like ointments and pastes

Oil and waxes contain surfactants, glycol depends on formulation and drug solubility

Question 11

How do you target a normal intact stratum corneum to enhance skin delivery

Answer 11

1. Aqueous or oil based formulations containing alcohols, glycols, oleic acid
2. Isopropyl myristate, propylene glycol

Question 12

What is the typical bioavailability of topical creams and gels and patches

Answer 12

1. Topical creams and gels: 1-3%

2. Patches: 30-70% of drugs

Question 13

What is the most appropriate properties the formulation of drug should have

Answer 13

1. Designed to have appropriate release of drug, rapid release or slow (7 day patch)
2. Contains MODERATELY LIPOPHILIC DRUG in LIPOPHILIC OILY BASE
3. Vehicle should allow solubility of drug but not retain the drug by being a good solvent

Question 14

What is the most desirable thermodynamic property

Answer 14

Saturated solutions: Kp is fixed for given molecule

Gives maximum driving force for diffusion, maximum concentration gradient through skin

Question 15

What does occlusion allow and give an example of a product that uses this

Answer 15

1. Helps stratum corneum equilibrate with underlying wet epidermis
2. Stops transepidermal water loss (TEWL)
3. Hydrates tissue
4. Promotes delivery of hydrophilic and hydrophobic compounds
5. Product: EMLA cream applied with occlusive dressing

Question 16

What is an enhancer

Answer 16

1. Chemicals that interact reversibly with skin to promote drug flux
2. Typical: disrupts stratum corneum and intercellular lipid structure
3. Alters transcellular keratin conformation

Question 17

Give an example of an enhancer

Answer 17

Solvents: EtOH, propylene glycol
Surfactants: SLS
Fatty acids, oleic acid 
Urea
Mineral oils, silicone oils

Question 18

What is bioequivalence in comparing hydrocortisone and clobetasol

Answer 18

No significant difference in rate and extent of absorption

Question 19

What is the most common patch and describe what it consists of

Answer 19

1. Drug in adhesive (DIA)
2. Pressure sensitive adhesive, backing and release liner
3. Can incorporate solvents, surfactants and fragrances

Question 20

What are the advanced formulations used in drug skin delivery

Answer 20

1. Heat- double delivery
2. Ablation of skin; lasers and radio waves
3. Similar principle when treating wart- remove callus skin

Question 21

What is a liposome

Answer 21

1. Lipid vesicles that enclose an aqueous volume
2. Formed from phospholipids and possibly cholesterol
3. Can trap hydrophilic molecules in an aqueous core or lipophilic materials within membrane

Question 22

Give examples of liposome

Answer 22

1. Niosomes: non ionic surfactant
2. PEGylated: increases circulation residence
3. Ethosomes: high ethanol content, soft phospholipid vesicles
4. Transfersomes: derformable liposomes

Question 23

An example of a commercial liposome

Answer 23

amBisome

Formed with amphotericin B in liposomes

Question 24

What are good targets for liposomes for which skin conditions

Answer 24

Pilosebacceuous units

Used to treat acne, cancers and for systemic delivery

Question 25

What is iontophoresis

Answer 25

Electrical charge used to repel ionic molecules e.g. positive canon repelled by positive cathode Drives molecule into skin Can also get convective flow of water

Question 26

What are micro needles used for and their future use

Answer 26

Penetrate into strateum corneum, but no pain receptors Delivery of large proteins, antibodies, hormones, vaccines