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3117 > Suspension > Flashcards

Suspension Flashcards

1
Q

what is a suspension

A

dispersion of finely divided solid particles in a liquid medium, which may be aqueous or non-aqueous

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2
Q

size of coarse suspension

A

particle size >1 micron

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3
Q

size of colloidal suspension

A

particle size <= 1 micron

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4
Q

applications for suspension

A
  1. oral
  2. injection
  3. external use
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5
Q

oral applications of suspension

A
  • provide means of administering insoluble drugs in liquid form
  • provide means of supplying distasteful drugs in a form pleasant to taste
  • provide an effective means of administering insoluble compounds for their absorptive or antacid properties in the treatment of gastric disorders
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6
Q

injection use of suspension

A

provide a means of sustaining drug release as depot therapy

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7
Q

external use of suspension

A

provide means of applying insoluble drugs to skin

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8
Q

desirable properties of suspension

A
  • chemically stable
  • low rate of sedimentation of particles
  • particles should be readily dispersed upon gentle shaking of container
  • size of particles should remain fairly constant throughout storage
  • should pour readily from container
  • suspensions for injection should flow readily through syringe needle
  • suspensions for external use should spread easily and yet not so mobile that they run off the surface when applied
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9
Q

stokes law

A

v= (2r^2 (p1-p2)g)/9n

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10
Q

flocculated suspension

A
  • aggregates in dispersed phase
  • rapid sedimentation rate
  • porous sediment forms on prolonged standing
  • relatively large volume
  • easy to redisperse
  • clear supernatant liquid
  • rheological property of concentrated suspension- plastic flow with thixotropy
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11
Q

deflocculated suspension

A
  • individual particles in dispersed phase
  • slow sedimentation rate
  • compact sediment (cake) forms on prolonged standing
  • relatively small volume
  • difficult to redisperse
  • cloudy supernatant liquid
  • dilatant flow
  • troublesome during production
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12
Q

important factors for formulation of a suspension

A
  1. dispersed phase
  2. liquid vehicle
  3. wetting agent
  4. flocculating agent
  5. thickening agent
  6. pH buffer
  7. preservative
  8. colorant, flavour, fragrance
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13
Q

dispersed phase

A

aka suspensoid, consisting of insoluble solid particles: lyophilic and lyophobic

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14
Q

lyophilic solid

A

solvent-loving and do not require the use of wetting agent for dispersion in the liquid vehicle; may also increase the viscosity of suspension

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15
Q

lyophobic solid

A

not solvent-loving and require the use of wetting agent for dispersion in the liquid vehicle, most drugs are hydrophobic

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16
Q

liquid vehicle

A

dispersion medium / continuous phase; may be aq or non-aq, usually is water

17
Q

wetting agent

A 
function to make the solid particles more penetrable by the dispersion medium, eg: replace air space in particle crevice
- usually pre-mixed with solid particles in the preparation of suspension
18
Q

moa of wetting agent

A
  1. reduce solid-liquid interfacial tension

2. imparts hydrophilicity to particle surface

19
Q

examples of wetting agent for aq dispersion medium

A
  1. surfactant: HLB 7-9 (eg. spans), used at concentrations below CMC
  2. hydrophilic polymers (eg. acacia, tragacanth xanthan gum, polyvinylpyrrolidone)
  3. polyhydric alcohols: miscible with water (eg. glycerin, propylene glycol, polyethylene glycols)
20
Q

flocculating agents

A
  1. electrolytes
  2. surface-active agents
  3. hydrophilic polymers
21
Q

electrolytes

A

affect the zeta potential which governs interparticulate repulsion/attraction, interparticulate attraction occurs when zeta potential is reduced below critical value

22
Q

low concentration of electrolyte

A
  1. 01-1%:
    - generally sufficient to reduce the zeta potential to just below the critical value for interparticulate attraction to occur
    - van da waals attractive forces cause the solid particles to aggregate to form flocs
    - on prolonged standing, the flocs will settle to form a porous sediment which is easy to redisperse
23
Q

high concentration of electrolyte

A
  • reverse the sign of zeta potential and to a magnitude that will cause interparticulate repulsion
  • on prolonged standing, the particles will settle and form a compact sediment which is difficult to redisperse
24
Q

valence of electrolyte

A

effectiveness of electrolyte in aggregating particles increases with valence of ions

  • divalent ions are 10 times while trivalent ions are 100 times as effective as monovalent ion
  • monovalent ions are sufficient to induce flocculation of weakly charged particles
25
Q

surface-active agents

A
  1. ionic agents- behaving like electrolyte
  2. non-ionic agents- used at concentration above cmc, micelles adsorbed at surface of the particles, where they serve as bridges between particles; flocculation brought about by bridging mechanism between particles
26
Q

thickening agent

A

function to assist suspension of solid particles, achieved through thickening of dispersion medium

27
Q

example of thickening agent

A

gums, gelatin, bentonite, carboxymethyl cellulose, polyvinylpyrrolidone

28
Q

small scle dispersion techique

A
  1. mix solid drug with wetting agent in mortar
  2. add a small portion of liquid vehicle containing the additives to produce a pourable mixture
  3. transfer the mixture to measuring cylinder and make up to the required volume with remainder of the liquid vehicle
29
Q

large scale dispersion technique

A
  1. add wetting agent to solid (drug) in mixer
  2. add liquid vehicle containing additives
  3. transfer the mixture to high shear equipment to produce a good dispersion (excessive shearing should be avoided)
30
Q

precipitation technique

A
  1. organic solvent precipitation: water-insoluble drug is dissolved in water-miscible organic solvent and then added to distilled water under standard conditions
  2. pH-induced precipitation: only applicable to drugs whos solubility affected by ph
31
Q

stability of suspension

A

index of stability (F) = Volume of sediment at time t / initial volume of total suspension = Ht/Ho
more stable- less change in F over time

32
Q

redispersibility of suspension

A
  • mechanical device is used to shake the suspension which has been put aside for dispersed phase to settle down
  • the number of shakes required to disperse the sediment is determined
  • ease of dispersibility is inversely proportional to the number of shakes
33
Q

hydrophilic polymer examples

A

Acacia, tragacanth, alginates

34
Q

low concentration hydrophilic polymers

A

<0.05%

  • generally sufficient to bring about flocculation
  • adsorbed at surface of particles, where they serve as bridges between particles
35
Q

high concentration hydrophilic polymers

A

1 protective colloid effect 0.05-0.1%: polymer forms a protective coat around each particle, separating them from one another
2. viscosity-enhancing effect >0.1%: polymer increases the viscosity of the medium and improve stability but reduces flowability of the suspension

3117 (15 decks)

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