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PHA223 > co-solvents > Flashcards

co-solvents Flashcards

1
Q

What are co-solvents?

A

solute (drug) is more soluble in a mixture of solvents than in 1 solvent - ‘‘co-solvency’’
the solvent that increaes the solubility of the solute is called the co-colvent

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2
Q

What is a solution?

A

a homogenous, molecular, clear mixture of a solute dissolved in a solvent

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3
Q

What is the most common solvent?

A

water

- safety and low cost

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4
Q

What other things are used as solvents?

A

organic solvents

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5
Q

Why are organic solvents used?

A

not all drugs are soluble in water

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6
Q

How to enhance solubility of water insoluble drugs?

A

add water miscible liquid (co-solvent) which the drug will have a higher solubility
- organic solvent

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7
Q

What does an organic solvent need to be?

A

safe

miscible with water (water is most of the solution)

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8
Q

examples for co-solvents

A

glycerol
propylele glycol
polyethylele glycol
ethanol

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9
Q

What does the amount of co-solvent depend on?

A

their toxicity

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10
Q

factors to be considered

A
  1. SATURATION SOLUBILITY of the drug in water co-solvent mixture to avoid precipitation of the drug
  2. CONCENTRATION of the drug in the pharmaceutical solutions to give therapeutic effects
  3. LIMIT of the co-colvents
  4. does change in pH of the solution affect the solubility of the drug in water/co-solvent system?
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11
Q

example of a small drug molecule

A

paracetamol

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12
Q

example of macromolecule drugs

A

insulin

growth factor

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13
Q

Why should the conc of drug in solution be below its saturation solubility in the solvent?

A

to avoid drug precipitation and to enhance drug stability

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14
Q

How does the drug distribute via the solvent?

A

as molecules or ions

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15
Q

Can more than 1 co-solvent be used?

A

yes

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16
Q

Why are co-solvents used?

A

to increase the water (polar solvent) solubility of non-polar drugs with no ionisable groups

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17
Q

How do co-solvents work?

A

reduce the polarity of water and increase drug aqueous solubility

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18
Q

What increases drug solubility?

A

linear increase in co-solvent fraction leads to increase in drug solubility
-> inc co-solvent inc solubility of drug

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19
Q

mesurement for solubility (y axis)

A

% w/v

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20
Q

most common alcohol used as a co-solvent

A

ethanol

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21
Q

examples where ethanol is used as a co-solvent

A

orals (Elixirs)
topical
parenteral

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22
Q

structure of ethanol

A

CH3-CH2-OH

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23
Q

When is propylene glycol used?

A

oral
topical
parenteral
ear

24
Q

structure of propylene glycol

A

CH3CH(OH)CH2OH

25
Q

When is polyethylene glycol used?

A

parenteral solutions

26
Q

When is glycerol used as a co-colvent?

A

oral

parenteral

27
Q

structure of glycerol

A

C3 H8 O3

28
Q

How to determine saturated drug solubility in water/co=solvent mixtures?

A

shake flask method for the drug suspension in different mixtures at different temperatures

different proportions of water:co-colvent used
-> until you see drug precipitate (super saturation)

shake until they reach equilibrium (about 48hrs0

repeat experiment at least 3 times

filtration of the suspension and determine the drug soluble fraction in the supernatant

29
Q

Why are co-solvents important for pharmacsutical solutions?

A
  • rapid action
  • drug is in a molecular form, ready for absorption
  • dose uniformity (diff to suspension, need to shake)
  • patient compliance (elderly/children)
30
Q

What is preferential HYDRATION of a protein?

A
  • exclusion of the co-solvent from the protein surface due to steric effects/charge effects
  • more water molecules around the protein
  • protein is fully hydrated and stabilised
  • thermodynamic, increases free energy
31
Q

What is preferential BINDING to a protein?

A
  • cosolvent binding to protein surface
  • non-specifically or binding to specific sites on the protein surface
  • if it binds to active site it will inactivate enzymes
  • > cosolvent not working properly
32
Q

How many glucose units in cyclodextrins (alpha, beta, gamma)

  • how does this compare to the diameter of the hole
  • solubility of each
A

alpha

  • 6 glucose units
  • diameter = 0.5 nm
  • solubility = 14.2

beta

  • 7 glucose
  • 0.6 nm
  • 1.85

gamma

  • 8 glucose
  • 0.8 nm
  • 23.2
33
Q

structure of cyclodextrins

A
  • polar outer surface (dissolves in water)
  • less polar inner cavity
  • > hydrophobic drug molecules can fit inside, will still be hydrophilic on outside
34
Q

benefits of using cyclodextrins

A
  • inc bioavailability of hydrophobic drugs
  • enhanced of absorption of hydrophobic and hydrophilic drugs
  • lack of toxicity
  • inc stability of peptide hormones
  • can include volatile oils
  • onversion of liquid drugs to solid powders
  • masks taste
  • prevent drug-excipient interactions
35
Q

What is a saturated solution?

A

when equilibrium is present between un-dissolved and dissolved solute

36
Q

What is solubility?

A

the amount of solute that passes into solution to start the equilibrium at constant temperature and pressure to produce the solution

37
Q

What happens with a supersaturated solution?

A

excess solute will precipitate

  • > can’t dissolve any more drug in the solution
  • > drug will precipitate, can see it
38
Q

units for solubility

A

weight/volume - kg/m cubed (SI units)

1g/L

% w/v

% w/w

mole fraction

39
Q

What is mole fraction?

A

no of moles of solute (n1, drug) / total no of moles of solute and solvent (n2)

n1 / (n1 + n2)

40
Q

What does very soluble mean?

A

< 1g of solvent is needed to dissolve 1g of solute

41
Q

What does freely soluble mean?

A

1-10g of solvent needed to dissolve 1g of solute

42
Q

non-polar solutes in a polar solventts?

A

will not dissolve

  • no force of attraction/weak force
  • solutes will not disperse
  • > solute precipitates
43
Q

How to overcome attraction between solute molecules? (when they don’t attract)

A

co-solvency

44
Q

solute + co-solvent

A

= solution

45
Q

factors affecting solubility of solids in liquids

A
  • nature of solvents
  • solute characteristics (crystals, particle size)
  • excipients (solubilising agents)
46
Q

What scale of polarity is used for a solute?

A

oil:water partition coefficient

K o/w

47
Q

formula for logP

A

log K o/w = log P

48
Q

What is the logP for lipophilic drugs (un-ionisable)?

A

logP > 1

49
Q

What solvents do lipophilic drugs that are un-ionisable use?

A

can’t use non-aqueous solvents
esp for injections
(logP >1)

50
Q

conentration of ethanol used as a co-solvent

- why can’t more than this be used?

A

10%

- over this will cause haemolysis, pain

51
Q

What other thing needs to included in injection formulations as well as co-solvent?

A

isotonic salts

52
Q

What should the dielectric constant be for water miscible solvent?

A

dielectric constant between 25 and 80

53
Q

dielectric contant of water

A

80 (safe)

54
Q

What solvent cannot be used in pharmaceutical preparations?

A

methanol

  • > toxic
  • > can be used for separation and extraction
55
Q

examples of co-solvents

A 
water
ethanol
propylene glycol
glycerol
PEG 300/400

PHA223 (43 decks)

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