suspension Flashcards
what is the size of suspensions
0.5 micrometer it is is obaque
what is a suspension
dispersion of undissolved drug in saturated solution
what are reasons for suspension formulations
poor solubility of drug drug stability ease of administration rapid effect palatability injection provide sustained release
what is the reason for mixtures
better availabilty reduced gastric irritation improved effectiveness overcome oesaphegael retention ease of adm reduce unpleasent taste
what are indiffusible solids
do not easily disperse in water, hydrophobic and poorly wetted and dispersed need wetting and dispersing agent
wetting of powder q
decreased contact of angle more wettable
layer of absorbed sair may prevent a solid being wtted
use less ploar liquids can displace air and allow wetting
surfectants may be needed
what are suspending agents
tragacanth mucilage, sodium cmc, sodium alginate, carbopol & bentonite
what is the long term storage of suspension
remain suspended; very difficult in the long term
pour easily
re-disperse any sediment easily
maintain bioavailability; avoid crystal growth
why is it important that the suspension is formed by fine particle size
increased free energy
thermodynamic instability arises from large particle size resulting to caking.
delta g equates to interfacial change times by change of area
what happens when repulsion is high
deflocculated
what causes sedimentation
gravity eventually as bm has hardly any effect. large paricles sediment first then smaller particles. weight causes them to aggregate and form a cake the primary minimum.
what are ways to minimise irreversible caking
controlled flocullations, deflocculated with structured vehicles and both together q
what is principle of flocculations
keep suspension in secondary mimum so that there is attracted but remain separed loosely flocculated sediments. in suspension due to size and irregular shape of particles there is reduced point of contact and surfectans prevent close contact thus can form at primary minimum aswell. size of particles means significant kinetic energy is acheived to be redispersed
whats is deifference between deflocculated and flocculated suspension
d- small v of sediment, close packing and difficult to redisperse
f- one giant particle, high v of sediment and easily redispersed
how do we calculate sedimentation volume and elaborate on it
f= Vu/Vo
Vu ultimate volume of sediment
Vo original volume of sediment
The bigger the better
