Rheology of Suspensions

7/24/2019 Rheology of Suspensions

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dispersed system

Liquid preparations containing undissolved orimmiscible drugdistributed throughout a vehicle.

In these preparations, the substance distributed isreferred to as the dispersed phase, and the vehicle istermed the dispersing phase or dispersion medium.

Suspension: The particles of the dispersed phase areusually solid materials that are insoluble in thedispersion medium.

Emulsions: the dispersed phase is a liquid that is

neither soluble nor miscible with the liquid of thedispersing phase.

In the case of anaerosol, the dispersed phase may besmall air bubbles throughout a solution or an

emulsion.


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oarse !ispersions- Suspensions- Emulsions


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Suspensions

A pharmaceutical suspension is a coarsedispersion in which insoluble solid particlesare dispersed in a liquid medium.

The particles have diameters for the mostpart greater than 0.1 m


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S!"#E$TS T% &'S$!SS "easons #or Suspensions

#eatures !esired In $ %harmaceutical

Suspension Sedimentation "ate &f The

%articles &f $ Suspension

Evaluation &f SuspensionsEvaluation &f Suspensions


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T(pes of suspension

#locculated Suspensions:#locculated Suspensions:Suspension in which particles are wea)l( bondedSuspension in which particles are wea)l( bonded

settle rapidl( do not form a ca)e and are easil(settle rapidl( do not form a ca)e and are easil(

resuspended with a minimum of agitation.resuspended with a minimum of agitation.

!e'occulated Suspension:!e'occulated Suspension:

Suspension in which particles settle slowl( andSuspension in which particles settle slowl( and

eventuall( form a sediment in which aggregationeventuall( form a sediment in which aggregation

occurs with the resultant formation of a hard ca)eoccurs with the resultant formation of a hard ca)ewhich is di*cult to resuspended.which is di*cult to resuspended.


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Interfacial %roperties ofSuspended %articles

The large surface area of the particles thatresults from the grinding is associated with asurface free energ( that ma)es thes(stem thermodynamically unstable b(

which we mean that the particles are highl(energetic and tend to regroup in such a wa(as to decrease the total area and reduce thesurface free energ(.

The particles in a liquid suspension therefore

tend to focculate that is to form light ,u(conglomerates that are held together b(wea) van der aals forces.


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Sedimentation Parameters

The sedimentation volume F is de/ned asthe ratio of the /nal or ultimate volumeof the sediment Vu to the original volume

of the suspension Vo before settling


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I()"E!IE(TS of S*S%E(SI&(I()"E!IE(TS of S*S%E(SI&(

I +I + Insoluble drug.Insoluble drug.

II+ ehicle -suspending medium.II+ ehicle -suspending medium.

III+ /etting agents.III+ /etting agents.

I+ ompounds allowing control of stability andI+ ompounds allowing control of stability and

sedimentation -#locculating, Suspending agentsedimentation -#locculating, Suspending agent

+ $dditives used to regulate the 'ow behavior. + $dditives used to regulate the 'ow behavior.

I+ p0 regulatorsI+ p0 regulators

II+ &ther additives - 'avour, colour, tasteII+ &ther additives - 'avour, colour, taste

preservatives.preservatives.


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etting agentslocculating AgentsSuspending agents


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1. Surface-active agents:

2.Hydrophilic colloids

2.Solvents

wetting agents


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#locculating agents#locculating agents

1+ Electrolytes1+ Electrolytes

3+ Surfactants3+ Surfactants

2+ %olymers2+ %olymers 4+4+$lteration in the p0 of the$lteration in the p0 of the

preparation -generally to the regionpreparation -generally to the region

of minimum drug solubility.of minimum drug solubility.


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suspending agents1. Polysaccharides -

Acacia - Tragacanth - Alginates - Starch - Xanthan gum (Keltrol)

2. Water-soluble celluloses - ethylcellulose (!elacol" ethocel)

- #ydro$yethylcellulose (%atrosol)

- !armellose sodium (sodium carbo$ymethylcellulose)

- icrocrystalline cellulose

3. Hydrated silicates + bentonite, magnesium aluminum silicate and

hectorite

4. arbomers !carbo"ymethylcellulose #$. olloidal silicon dio"ide !%erosil#


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%"E%$"$TI&(

S*S%E(SI&(S

S!"#E$TS T% &'S$!SS

0ow to prepare a suspensions %ac5aging and storage of suspensions

!ry powders for oral suspension

"heology of suspensions


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An eample formula for an oralsuspension

$luminum hydro6ide compressed gel237.8 g

Sorbitol solution 383.9 mL

Syrup 2.9 mL )lycerin 3;.9 mL

Rheology of Suspensions

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