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form and tech > suspensions > Flashcards

suspensions Flashcards

1
Q

suspension definition

A

finely divided solid particles dispersed in liquid medium

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2
Q

coarse vs colloidal suspension particle sizes

A

coarse > 1 micron

colloidal is 1 micron or less

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3
Q

what kind of medium normally used for suspensions

A

can be aq or non aq but pharm suspensions normally are aq

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4
Q

suspensions oral use

A
  • administer insoluble drugs in liquid form
  • supply distasteful drugs in a form w pleasant taste
  • administer insoluble compounds for their absorptive or antacid properties in the treatment of gastric disorders
    eg activated charcoal which absrobs toxins , mg hydroxide aloh , calcium carb or sodium bicarb etc
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5
Q

suspensions for injection

A
  • sustaining drug release as depot therapy - meaning release in slow and sustained manner
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6
Q

suspensions for external use

A

means for applying insoluble drugs to the skin

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7
Q

desirable properties of suspensions (7)

A

stabl
low sedimentation rate
easily redispersed upon shaking
size of particle shld remain fairly constant throughout storage
pour readily
suspensions for injection shld flow readily thru needle
suspensions for external shld spread easily but not run off surface of site

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8
Q

which trait preferred for suspensions and why

A

thixotropy

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9
Q

recall stokes law

A

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

velocity 
radius of particle 
density of particle- density of dispersion medium 
gravitational constant (6.67 x 10^-11) 
viscosity of dispersion medium
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10
Q

recall why stokes law not directly applicable

but what can be done

A
  • used for isolated sphere in infinitely large mass of liquid but factors can help to modify sedimentation rate

eg - inc size of particle
inc viscosity of the medium
dec the difference in density - altho hard to modify

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11
Q

dispersed particles and floccules form what kidn of suspension

and differentiate them according to 
- sedimentation rate 
nature of final sediment 
nature of supernatant liquid 
rheological property of conc suspension
A

floccules form flocculated suspension ( like clotted )
deflocculated form deflocculated suspension ( cloudy )

flocculated 
- rapid sedimentation rate 
- forms porous seidment on standing 
large volume bc of big interparticular space and is 
easy to redisperse 
- clear supernatant 
- plastic flow with thixotropy

deflocculated
- slow sedimentation rate
- forms a cake ( compact sediment ) on standing
small volume and difficult to redisperse
- cloudy supernatant
- dilatant flow !! troublesome

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12
Q

how to determine degree of flocculation

A
  • allow suspension to stand til vol of sediment becomes constant V t
  • centrifuge and determine volume of sediment ( Vc)
    ( this breaks down the flocs due to centrigual force
    forming a compact, space reduced to min )
  • greater the ratio of Vt to Vc = greater flocculation
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13
Q

whats needed in the formulation of suspensions 5 + 3

A 
dispersed phase 
liquid vehicle 
wetting agent 
flocculating agent 
thickening agent 
other additives : ph buffer, preservatives, colourants flavour or fragrance
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14
Q

dispersed phase 2 types and what they consist of

A
  • aka suspensoid
  • consist of insoluble solid particles

lyophilic - solvent loving and dont need wetting agent for dispersion
- may inc viscosity

pyophobic - not solvent loving and needs wetting agent for dispersion
- most drugs are hydrophobic

note that solvent loving dosent mean soluble

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15
Q

liquid vehcile aka
what type and
commonly used

A
  • aka dispersion medium or cont phase
    may be aq or non aq
    water commonly used
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16
Q

wetting agent func and 2 MOA

A

make solid particle more penetrable by the dispersion medium

moa 1: reduce solid liquid interfacial tension
moa 2- imparts hydrophilicity to the solid particle surface
imagine there are air crevices around the particle the wetting agent fills that up

17
Q

when are wetting agents added

A

mixed in with the solid particles in the preperation

18
Q

3 examples of wetting agents

A
  1. surfactants of hlb 7-9 aka spans
    used @ conc below the cmc
  2. hydrophilic polymers like acacia, tragacanth, polyvinylpyrolidone and xanthan gum
  3. polyhydric alcohols
    - misicble w water
    for eg glycerin , propylene glycol, polyethylene glycols
19
Q

what is not allowed in oral suspensions due to toxic effects

A

diethylene glycol

20
Q

3 types of flocculating agents

A

electrolytes
surface active agents
hydrophillic polymers

21
Q

moa for electrolytes

A

1st class of flocculating agents
- affect Zeta potential which governs the interparticulate attraction or repulsion
- if zeta potential is reduced below critical value
= attraction

if low conc of electrolytes 0.01-1%
- sufficient to reduce ZP below critical conc
= int part attraction
= VD forces cause solid particles to aggregate and floc
= upon settling flocculates aggregates form which are easily redispersed

if high conc used

  • reverses the sign of ZP til int pat repulsions occurs
  • upon standing forms compact sediment which is difficult to redisperse

valency also v impt according to schulze -hardy rule
monovalent
divalent x 10
trivalent x 1000 more effective as aggregating particles

monovalent sufficient to induce flocculation if particles are weakly charged

22
Q

moa of surface active agents

A 
2nd class of flocculating agents 
2 types 
if ionic then they behave as electrolytes

if non ionic
- must be used at conc above cmc
- micelles adsorb onto surface of particles
= serve as bridges
= bridging mechanism allowed flocculation to occur

23
Q

diff between ionic agents and electrolytes

A

ionic agents bigger than electrolytes

electrolytes are like sodium chloride and phosphates

24
Q

moa of hydrophilic polymers

A 
3rd class of flocculating agents 
eg acacia, tragacanth, alginates

low conc < 0.05% = bridging mechanism

high conc 
1. protective colloid effect 0.05-0.1% 
polymer form protective coat aroudn the particle 
2. viscosity enhancing effect >0/1% 
long molecules of polymer form network in the liquid 
= inc viscosoty 
= inc stability 
= red flowability
25
Q

func of thickening agent an dmoa

A
  • assist in suspension of solid particles
    thru thickening of dispersion medium
    eg - gums, gelatin, bentonite clay , carboxymethyl cellulose and polyvinylpyrollidone

effects depending on conc
flocculating effect if conc <0.05%
protective colloid effect 0.05-0.1%
viscosity enhancing effect if > 0.1%

26
Q

notes for ph buffers in formulation

A

for optimal stability

but dont use unless rlly need

27
Q

notes for preservaives

A

control microb contamination

cationic presrvatives not reco

28
Q

notes for flavours, fragnants and colourants

A

could dec stability

29
Q

large scale and small scale prep of suspensions

A

small

  • mix solid drug w wetting agent in motar
  • add small pop of liquid vehicle w additives to produce pourable micture
  • transfer mixture to a measuring cylinder and make up required vol with remaining liquid vehicle

large
- add wetting agent to the solid drug in mixer
- add vehicle containing additives
- transfer mixture to high shear equipment to produce good dispersion
( avoid excessive shearing )

30
Q

describe the precipitation technique of producign suspension
2

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

how to evaluate stability of suspension

2 methods

A

(1) transfer freshly prepared suspension to measuring cylinder and determine vol of sediment @ different time intervals
F = Vt /Vo
index of stability = vol of sedimen @ time t / initial vol of total suspension

and vol is proportional to height

F = 1 @ time t=0 , over time F < 1

DRAW THE PLOT , more deviation from 1 = less stable

(2) testing redispersibiliyt
- put suspensiona side for dispersed phase to settle down
- use mechanical device to shake
- determine number of shakes needed to redisperse the sediment
- ease of redispersibility inversely prop to number of shakes

form and tech (9 decks)

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