colloids Flashcards
What is a colloid?
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance.
What is topical delivery
Delivery of a medicament to the skin or mucous membrane.
What is local delivery?
Delivery of active agent to skin tissue e.g. emollient
What is systemic delivery?
Transdermal- delivery of drug across skin and into the dermal blood vessels and into systemic circulation
What must drugs cross for local or systemic drug delivery?
The stratum corneum
What is the brick and mortar model?
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.
What factors effect the rate of drug absorption across the skin?
- 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
What is the rate limiting step of absorption?
- The stratum corneum- drug must partition into the SC before diffusing across epidermal layers
What equation can be used to predict rate of drug transport across the skin?
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
How can you increase rate (flux) of drug across the skin?
- 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
What is the Potts and Guy equation?
kp= 0.71 x log k (octanol/water o/w)- 0.0061x mw-6.3
kp= permeability coefficient cm/time
Factors affecting rate of transdermal drug transport?
- 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
What are the two types of transdermal patch?
- Monolith
- Rate-limiting membrane system
What is microneedles delivery?
- As large molecules can’t diffuse through the skin it uses tiny needles to penetrate the epidermis and directly deliver the drug
What is iontophoresis?
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)