Oral (Suspensions) Flashcards
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
gravity
external agitation (e.g. shaking)Dif
Diffusion…
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
