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Flashcards in Oral (Suspensions) Deck (19)
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What is a disperse system?

a two-phase heterogeneous system in which an insoluble or immiscible dispersed phase is distributed through a continuous phase.


What is a pharmaceutical suspension?

a liquid disperse system consisting of particles distributed within a liquid vehicle

appear cloudy


How can we ensure a uniform dose in an oral suspension? (3)

particles should settle slowly

particle size remains constant over time

viscosity is high enough


The electrical double layer is when..

the water molecules undergo self-ionisation reactions and produces ion/charges
H+ and OH-

the system needs to maintain an overall neutral charge. Cations form a layer around the solid particle to form the electrical double layer.


Ionic salts increase the number of..

mobile charges

at lower conc - will only affect diffuse layer, easier to neutralise the particle charge

higher conc - will affect the fixed layer, charge on the particle surface will decrease


DLVO theory..

explains the aggregation of aqueous dispersions and the forces between charged surfaced interacting within the liquid

predicts if particles will settle or remain homogeneously dispersed


What is a deflocculated system?

A system in which particles are individually and uniformly dispersed throughout the liquid medium

may settle slowly over time resulting in sediment at the bottom of the suspension


What is a flocculated system?

A system at which suspended particles are formed in floccules rather than separate particles

when attractive forces are greater than repulsive


Particle movements caused by: (3)

Brownian motion
external agitation (e.g. shaking)Dif



Small particles are subject to Brownian motion - high conc to low

less likely in flocculated systems as particles are larger


What decreases diffusion?

Increased medium viscosity


Sedimentation is..

the downward particle movement due to gravity


What decreases sedimentation?

reducing particle size
increasing viscosity
increase temp (would increase diffusion constant)
reduce particle density (but this increases particle size)


2 options for controlling sedimentation:

- a deflocculated system with minimal sedimentation which will require greater viscosity to maintain dispersion

- a flocculated system with controlled slow sedimentation


Excipients to improve palatability..

flavours, sweeteners, colourings

e.g. saccharin

but need to consider their effect on the electrical double layer


Why are preservatives added?

to prevent microbial growth

sorbic acid and benzoic acid


Why are buffers added?

to maintain pH of aqueous system


Why are suspending agents added?

to reduce particle sedimentation

e.g. water soluble cellulose polymers
hydroxypropyl methylcellulose
released NA+ ions

e.g. sodium alginate
easily ionised


Flocculating agents are added to..

adjust the flocculation status of the particles after taking into account the combination effects of all excipients.