colloids Flashcards

1
Q

What is a colloid?

A

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

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2
Q

What is topical delivery

A

Delivery of a medicament to the skin or mucous membrane.

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3
Q

What is local delivery?

A

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

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4
Q

What is systemic delivery?

A

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

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5
Q

What must drugs cross for local or systemic drug delivery?

A

The stratum corneum

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6
Q

What is the brick and mortar model?

A

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.

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7
Q

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

A
  • 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
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8
Q

What is the rate limiting step of absorption?

A
  • The stratum corneum- drug must partition into the SC before diffusing across epidermal layers
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9
Q

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

A

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

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10
Q

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

A
  • 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
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11
Q

What is the Potts and Guy equation?

A

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

kp= permeability coefficient cm/time

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12
Q

Factors affecting rate of transdermal drug transport?

A
  • 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
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13
Q

What are the two types of transdermal patch?

A
  • Monolith
  • Rate-limiting membrane system
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14
Q

What is microneedles delivery?

A
  • As large molecules can’t diffuse through the skin it uses tiny needles to penetrate the epidermis and directly deliver the drug
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15
Q

What is iontophoresis?

A

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)

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16
Q

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

A

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.

17
Q

What does a low/negative logK indicate

A

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

18
Q

What does a high log K indicate

A

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

19
Q

Why may an ointment have a higher flux rate?

A

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

20
Q

Why may an ointment have a higher flux rate?

A

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