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SL12102 - the science of medicines > L19 - drug sol & dissolution rate 4 > Flashcards

L19 - drug sol & dissolution rate 4 Flashcards

1
Q

class 1 drug

A
  • high solubility
  • high permeability
    e.g simple oral dosage form
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2
Q

class 2 drug

A
  • low solubility
  • high permeability
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3
Q

class 3 drug

A
  • high solubility
  • low permeability
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4
Q

class 4 drug

A
  • low solubility
  • low permeability
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5
Q

how do cyclodextrins work?

A
  • inclusion compounds
  • bring molecule into solution
  • made by putting non-polar part of one molecule into non-polar cavity of a water-soluble molecule
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6
Q

describe the structure of cyclodextrins (CD)

A
  • enzymatically modified starches so less toxic
  • cylindrical ring
  • hydrophilic outer surface
  • cavity is lipophillic/ non-polar
  • glucopyranose units forms ring of 6 units, b-CD units, g-CD 8 units
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7
Q

what is the host guest ratio of CD usually?

A

1:1 so lipophilic molecules can be wholly or partially accommodated for in a complex

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8
Q

dissolution- dissociation- recrystallise process of CD complex of a poorly soluble guest

A
  • crystalline complex is soluble in water
  • outer shell is dissolved
  • so CD can leave complex
  • this is an easy way to increase solubility of drug in short time that is not otherwise soluble in water
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9
Q

how has β-cyclodextrin been used to improve the solubility of ibuprofen?

A
  • mixture of ibuprofen and CD produces complex in water bath (dissolution medium)
  • dissolution tests show an increase in dissolution rate of ibuprofen
  • comparing dissolution profiles has show that at a low pH there is a bigger effect of the complex on the release of ibuprofen (low solubility in water)
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10
Q

adverse effects of CD

A

β-cyclodextrins have found a way to be used as controlled release of drug

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11
Q

what are surfactants?

A

surface active agents

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12
Q

what could the ability to reduce surface tension at an interface without needing large concentrations do?

A

blur the difference between solvent and solute

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13
Q

what are most marked events obtained with?

A

solutes that combine in their molecule structure
- one element has a high affinity for solvent
- one doesn’t
e.g phospholipid

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14
Q

what does the balance between hydrophilic part and hydrophobic part of molecule determine?

A
  1. surfactant solubility in water and oil
  2. surfactant applications
  3. place on scales of hydrophile-lipophile balance (HBL)
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15
Q

describe the polar region

A
  • high affinity for water
  • can pull long hydrocarbon chains into water
  • must be polar enough to hold non-polar region in solution
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16
Q

4 classifications of surfactants

A
  1. anionic
  2. cationic
  3. non ionic
  4. zwitterionic
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17
Q

properties of surfactants at dilute solutions

A
  • surfactants act as normal solutions and electrolytes
  • the amphiphiles exist separately
  • size of amphiphiles causes them to be sub-colloidal
18
Q

define subcolloidal

A

solution is mixture of 2 substances where insoluble particles of one substance are suspended throughout the other substance on a microscopic scale

19
Q

properties of surfactant solutions at concentrated solutions

A
  • surfactants aggregate/ come together over narrow concentration range
  • aggregates = micelles
20
Q

Critical micelle concentration (CMC)

A

conc of monomer at which micelles form

21
Q

aggregation number of micelles

A

number of monomers that aggregate to form a micelle

22
Q

micellisation

A
  • alt mechanism to adsorption (molecules stick to surface)
  • allows strong water water interactions that would not happen if surfactant molecules were in solution as single molecules between water molecules (hydrophobic effect)
23
Q

what happens as you increase surfactant?

A

they arrange so head faces water and tails face away

24
Q

what happens if you increase conc of surfactant even more?

A

they self aggregate

25
Q

at CMC what are the changes in physical properties of surfactants?

A
  1. osmotic pressure
  2. turbidity
  3. electrical conductance
  4. surface tension
26
Q

as you add surfactant what happens to osmotic pressure?

A

increases, then CMC is achieved so it stabilises

27
Q

as you add surfactant what happens to turbidity?

A

a small increase, but after cmc is achieved there is a huge increase

28
Q

as you add surfactant what happens to surface tension?

A

decreases, then once cmc is achieved (once micelle formation is achieved) it stabilises

29
Q

as you add surfactant what happens to molar conductivity?

A

decreases, then cmc is achieved and it decreases even more

30
Q

factors affecting cmc (micelle formation) IMPORTANT

A
  1. CMC increases as polarity of head increases
  2. CMC decreases with:
    - temperature (cloud point)
    - pH (remember surfactants are weak electrolytes)
    - second surfactant
    - addition of electrolytes and organic matter
31
Q

effect of carbon chain on length of CMC?

A

as carbon chain increases (tail) but polar head stays same, CMC will DECREASE.
as at longer chain length the system becomes more unstable thermodynamically.

32
Q

critical values for micelles

A
  1. CMC
  2. Kraft point (critical micelle temp)
  3. cloud point
  4. critical micelle pH
33
Q

the Kraft point

A

temp at which solubility becomes equal to cmc

34
Q

at a temperature below the Kraft point describe cmc and solubility

A

cmc will be bigger than solubility and micelles will not be able to form

35
Q

when the temperature is above the Kraft point explain what happens

A

surfactant forms micelles, self-solubilisation

36
Q

unassociated surfactant has ?

A

limited solubility

37
Q

micelles are?

A

highly soluble and can acclimate a large amount of surfactant

38
Q

cloud point

A
  • non ionic surfactants
  • increase in temp causes
    1. dehydration of cahains
    2. decrease in water sol
    3. formation of large micelles
    so solution becomes cloudy
39
Q

reversible process for cloud point

A
  1. cooling
  2. formation of small micelle and clarification
40
Q

critical micelle pH

A
  • if ionised form of compound is surface active
  • and unionised form is inactive
  • or has lower cmc than ionised form
  • than pH can induce micellisation

SL12102 - the science of medicines (26 decks)

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