P11, P12 & P13: Topical Drug Delivery

Question 1

what is the structure of the stratum corneum

Answer 1

bricks= dead keratin-filled cells
mortar= complex lipid mixture
has rivets holding corneocytes together are specialised protein structures called corneodesomes

Question 2

what are corneodesomes

Answer 2

major structures to be degraded for desquamation of the skin

Question 3

what are the pathways through the stratum corneum

Answer 3

transcellular

intercellular

Question 4

via which pathway does H2O cross the stratum cornea

Answer 4

intercellular

Question 5

what is the drug/delivery system supposed to do

Answer 5

modulate barrier function, treat disease states in the epidermis an dermis, alleviate local pain/inflammation in subcutaneous tissues, elicit systemic pharmacological effect

Question 6

where is the therapeutic target and how accessible is it

Answer 6

surface, stratum corneum, viable epidermis/dermis, skin appendages, suncutaneous tissue, systemic circulation

Question 7

what happens during percutaneous absorption

Answer 7

absorption of drugs from the skin surface into the body

drug penetrates into skin and is taken up by microcirculation

Question 8

what does percutaneous absorption depend on

Answer 8

physiochemical properties of a drug, interactions of drug with vehicle or delivery system and with the skin, condition of the skin

Question 9

how are topical formulations optimised

Answer 9

many are lipophilic with very low aqueous solubility

introduction of co-solvent into a formulation can increase Csat but this has the opposite effect on Ksc/v

Question 10

how does pH of vehicle influence absorption

Answer 10

skin surface pH is acidic
unionised drugs best absorbed
extreme pH values damaging to skin, formulations mostly neutral

Question 11

how does skin permeation affect absorption

Answer 11

some excipients, when incorporated in wehicle, can improve drug flux, but correlation between enhancement efficacy and skin irritation produced

Question 12

what is the ideal vehicle in drug formulation

Answer 12

elicits no pharmacological effects, solubilises the drug, releases the drug with appropriate kinetics, is chemically and physically stable, is cosmetically appealing, is non-allergenic and non-irritating

Question 13

what are the issues during drug formulation

Answer 13

interaction of vehicle with skin, interaction between drug and vehicle, no ‘rules’ for matching a formulation to a particular drug, enhancing delivery without irritating the skin

Question 14

what physiochemical considerations need to be made during drug formulation

Answer 14

MW, lipophilicity, H-bonding, solubility in different solvents

Question 15

how are formulations selected

Answer 15

type of emulsion, lipid content and occlusivity

Question 16

what type of formulation is preferred for chronic skin disease

Answer 16

hydrocarbon-based formulations

Question 17

how can drug solubility be enhanced

Answer 17

by formulation with hydrocarbon-miscible solvents like isopropyl myristate or propylene glycol

Question 18

what is the water-free PEG-gel formulation

Answer 18

polar, 1-phase, semi-solid system, based on polyethylene glycols

Question 19

what is the water-free lipogel formulation

Answer 19

polar, 1-phase, semi-solid system, principally based on triglyceride derivatives

Question 20

what is the water-free oleogel formulation

Answer 20

polar, 1-phase, semi-solid system compromising triglycerides and/or hydrocarbon/ silicon oils and inorganic filter

Question 21

what is the water-free fatty ointment formulation

Answer 21

apolar, 1-phase, semi-solid system, based on hydrocarbon materials

Question 22

what are water-free formulations used to treat

Answer 22

psoriasis, chronic eczema, mycosis

small area of application to very dry skin

Question 23

what is the base for polar gel formulations

Answer 23

water and/or alcohol-based with low lipid content or even lipid free
variety of gelling agents for thickening solutions and suspensions, allowing creatino of diverse formulations

Question 24

what is an emulsion gel

Answer 24

hydrogel containing a dispersed lipid phase

Question 25

what are suspension gels

Answer 25

suspensions of water-insoluble drugs in hydrogels

Question 26

what is hydrogel

Answer 26

semi-solid system, typically compromising large organic molecules inter-penetrated by water

Question 27

what is emugel

Answer 27

2-phase system, consisting of large organic molecules inter-penetrated by water and small fraction of emulsified lipids

Question 28

what are gel formulations used to treat

Answer 28

acne, acute eczema, allergic skin conditions | small application areas to normal-to-oily and inflamed skin, transparent to opaque semi-solid gels, rapidly absorbed

Question 29

what are emulsions

Answer 29

creams, disperse systems and the majority of aqueous formulations readily adjustable properties, require emulsifiers

Question 30

what are the features of w/o emulsions

Answer 30

blend easily with SC lipids, improving bioavailability of lipid-soluble drugs and moisturising skin via slight occlusive effect

Question 31

what are the features of o/w emulsions

Answer 31

more cosmetically appealing as lipids therein are finely dispersed can withdraw moisture from the skin due to surfactant-like emulsifiers

Question 32

what is w/o lotion

Answer 32

hydrophobic, semi-liquid, 2-phase system, compromising water and a continuous lipid phase

Question 33

what is w/o cream

Answer 33

hydrophobic, semi-solid, 2-phase system, compromising water and a continuous lipid phase

Question 34

what are w/o creams used to treat

Answer 34

psoriasis, chronic eczema, mycosis | broad areas of application to normal to dry skin

Question 35

what is o/w cream

Answer 35

hydrophilic, semi-liquid, 2-phase system, compromising lipids and a continuous aqueous phase

Question 36

what is o/w cream

Answer 36

hydrophilic, semi-solid, 2-phase system, compromising lipids and a continuous aqueous phase

Question 37

what are o/w creams used to treat

Answer 37

acne and acute and sub-acute eczema | broad areas of application to normal to slightly dry skin and to inflamed areas

Question 38

what is the absorption base of dermatological formulations

Answer 38

apolar, 1-phase, semi-solid system compromising mainly hydrocarbon structures

Question 39

what is the liposome formulation

Answer 39

bi- or multi-lamellar phospholipid structure entrapping a hydrophilic core

Question 40

what are nanoemulsions

Answer 40

vesicles of phospholipids, surfactant and other lipid dispersed un water

Question 41

what are microemulsions

Answer 41

transparent o/w or w/o colloidal emulsions compromising lipophilic and hydrophilic surfactants and water

Question 42

what are emulsifier-free systems

Answer 42

2-phase, semi-solid and hydrophilic, comprising various lipids, a continuous aqueous phase and polymers/co-polymers

Question 43

what are multiple emulsions

Answer 43

3-phase, semi-solid, hydrophilic (w/o/w) or hydrophobic (o/w/o) systems

Question 44

what are spray emulsions

Answer 44

stable, sprayable, 2-phase, semi-liquid emulsions

Question 45

what are foam/mousse formulations

Answer 45

gas dispersions in liquids containing lipids and water stabalised with surfactants

Question 46

what are water-free 2-phase systems

Answer 46

physical mixture of 2 non-miscible organic phases forming semi-solid stabalised with polymers/co-polymers

Question 47

what are lacquers

Answer 47

polymeric film-builders in volatile solvents and plasticiser leaving transparent, elastic and adhesive film on skin/nail

Question 48

what happens to formulations when they are applied to skin

Answer 48

structural matrix of formulation may change due to rubbing or loss of volatile excipients leading to increased viscosity rubbing may cause emulsifying effects