colloids

Question 1

What is a colloid?

Answer 1

A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance.

Question 2

What is topical delivery

Answer 2

Delivery of a medicament to the skin or mucous membrane.

Question 3

What is local delivery?

Answer 3

Delivery of active agent to skin tissue e.g. emollient

Question 4

What is systemic delivery?

Answer 4

Transdermal- delivery of drug across skin and into the dermal blood vessels and into systemic circulation

Question 5

What must drugs cross for local or systemic drug delivery?

Answer 5

The stratum corneum

Question 6

What is the brick and mortar model?

Answer 6

The structure of the stratum corneum is compared to brick and mortar as the corneocytes are the bricks and the lipid matrix surrounding Them is the mortar.

Question 7

What factors effect the rate of drug absorption across the skin?

Answer 7

• Concentration of drug applied to the skin- increase gradient across the stratum corneum- Fick’s law
• Diffusion coefficient of drug- influenced by size, shape and charge of drug- stokes Einstein
• solution partition coefficient- between skin and formulation- drug must partition onto stratum corneum before diffusing across epidermal layers

Question 8

What is the rate limiting step of absorption?

Answer 8

• The stratum corneum- drug must partition into the SC before diffusing across epidermal layers

Question 9

What equation can be used to predict rate of drug transport across the skin?

Answer 9

J = (Dp/𝛿) △Cv

j= flux (cm/s)
d= diffusion coefficient in stratum corneum
p= partition coefficient between formulation and skin
𝛿= thickness of stratum corneum
△Cv= concentration difference between formulation and skin

Question 10

How can you increase rate (flux) of drug across the skin?

Answer 10

• increase △Cv- maintains a high concentration of drug at the skin surface by using co-solvents to increase solubility or supersaturated drug formulations
• increase drug coefficient D= Drug is more lipophilic it masks polar groups or use absorption enhancers which liquidifies SC lipids

Question 11

What is the Potts and Guy equation?

Answer 11

kp= 0.71 x log k (octanol/water o/w)- 0.0061x mw-6.3

kp= permeability coefficient cm/time

Question 12

Factors affecting rate of transdermal drug transport?

Answer 12

• Time scale of drug exposure- creams OD/BD/TD, patches- OD or every 72 hours
• size and condition of the skin- sc thickness varies around the body and broken or inflamed skin is more permeable
• formulation- oil/cream/gel/lotion?
• skin hydration- hydrated skin- more permeability to drug due to loser packaging of SC lipids- less restrictive path for drug diffusion

Question 13

What are the two types of transdermal patch?

Answer 13

• Monolith
• Rate-limiting membrane system

Question 14

What is microneedles delivery?

Answer 14

• As large molecules can’t diffuse through the skin it uses tiny needles to penetrate the epidermis and directly deliver the drug

Question 15

What is iontophoresis?

Answer 15

Uses the driving of charged molecules through the skin using low electrical currents by applying a small current through the skin. e.g. Glycopyrronium bromide for hyperhidrosis (excessive sweating)

Question 16

What does the brick and mortar model dictate about polar compounds?

Answer 16

If drugs are ionic and hence polar, it is difficult for it to partition into the SC. the model dictates that polar compounds exploit a discontinuous route across the keratinocytes rather than through the continuous lipid phase that exists around the keratinocytes.

Question 17

What does a low/negative logK indicate

Answer 17

the drug will remain in a hydrophilic formulation e.g. gel rather than partitioning into sc

Question 18

What does a high log K indicate

Answer 18

That the drug is very lipophillic and in a gel It will partition readily into sc

Question 19

Why may an ointment have a higher flux rate?

Answer 19

due to its occlusive nature- causing hydration of the skin, it

Question 20

Why may an ointment have a higher flux rate?

Answer 20

due to its occlusive nature- causing hydration of the skin, it