MDM: suspensions Flashcards
What is a suspension?
Dispersion of fine insoluble solid particles (disperse phase) within a liquid (disperse medium/ continous phase)
What types of suspensions are there?
- Solid particles above 1um are course suspensions
- solid particles below 1um are colloidal dispersion
What are properties of a well formulated suspension?
- Disperse phase and particles snall, unifromly sized and not settle too rapidly
- Settled particles should not form a compacted sediment which is difficult to disperse
- doses should contain the same amount of suspended solid therefor the same dose of drug
- proucts should have an agreeable odour, colour, taste and texture
- continous phase should not support microbial growth
What are advantages of suspensions?
- easy to take and for people with swallowing issues
- bitter taste of many drugs less noticable in solid state than in solution
- high SA of fine suspensions gives fast dissolution rate
- high SA required for fast action of toxin absorbents
What are disadvantages?
- Bulky to carry around
- May require 5ml spoon/syringe
- sedimentation: flocculated - fast sedimentation but easy to redisperse. Deflocculated - slow sedimentation but difficult to redisperse. Both leads to inaccurate dosing
- Drug stability - presence of water can result in hydrolytic degradation
- ostwald crystal rippening
What is ostwald crystal rippening?
when small drug particles dissolude and recrystalise on the surface on a large particle causing a shift in mean particle size
What is aggregation and coagulation?
- Aggregation is a collection of individual particles into a group
- Coagulation occurs when particles approaching each other have sufficent energy to overcome repulsive forces - particles form compact aggregates. Compact aggregates can’t easily be broken down
What is stokes law? equation, parameters?
v=2a2g (σ-p) / 9n
v= rate of sedimentation
a= diameter of sphere
g = accerlation due to gravity
p = density of liquid
delta = density of sphere
n = viscosity of liquid
What are properties of a flocculated suspension?
- Rate of sedimentation fast
- large aggregated particles - denisty higher therefore sediment rate faster
- a
- resuspends easily
- sediment exhibits a higher volume due to loose open structure of floccules and large amount of liquid
- clear volume above sediment after a fewmin of shaking
What are properties of a deflocculated suspension?
- smal individula particles
- slow rate of sedimentation
- hard to redisperse
- particles sediment according to size - larger first
What is the F value?
Degree of sedimentation
F=Vs/Vt
F= sedimentation volume
Vs= volume of sediment
Vt= total volume of suspension
What are constants for F-value?
- same amount of drug in each suspension
- same dimentions of container
- measurements taken when sedimation complete
- F value higher for floc
What is B value?
The relation between sedimation volume of a flocc and deflocc suspension
B = F/F(infinity)
F= sedin volume flocc and de floc
What is a diffusable solid and what is an indiffusable solid?
- diffusable - insoluble solids that can be suspended in a continous phase for a sufficent time so that a dose can be measured
- indiffusable - an insoluble solid that is unable to stay suspended in a continous phase long enough for a dose to be measured without a suspending agent (CMC)
What should particle size be for a suspension?
- Small enough that rate of sedimentation is slow
- narrow size distribution to stop ostwald rippening
