Suspensions Part 2 Flashcards
explain what flocs/flocculated suspensions are
particles are weakly bound together (called flocs) when the forces of attraction are just slightly greater than the repulsive forces
true or false
flocculated suspensions rapidly undergo sedimentation
true
are flocculated suspensions readily re-suspended?
YES
flocculated suspensions have a______ sedimentation volume
large
what is the appearance of the supernatant in flocculated suspensions
supernatant = region on top of the suspended particles
will be CLEAR in flocculated suspensions bc even the smallest particles are involved in the flocs — will not be cloudy
_____ suspensions are also known as aggregated suspensions
DEflocculated
do deflocculated suspensions settle fast or slow?
slow
explain why and how deflocculated suspensions are not desirable
they will form a sediment (CAKE) eventually
bc the larger particles will settle faster and the small ones will fill in the voids between the large particles. thus, the lower most particles will be pressed together by the weight of the ones above
THIS IS DIFFICULT OR IMPOSSIBLE TO RESUSPEND ONCE CAKED
true or false
deflocculated suspensions initially have a pleasant appearance
TRUE
they will remain cloudy for a while after shaking
BUT —– will eventually form a cake
what is actually an advantage of deflocculated suspensions?
uniform dosing can be achieved – but only EARLY before the cake forms
this is bc the sedimentation occurs SLOWLY
true or false
deflocculated suspensions have poor physical stability/quality
true
in deflocculated/aggregated suspensions, explain the relationship between attractive and repulsive forces
the internal phase attraction is MUCH greater than repulsion - will form a cake
(however for defloc the attractive forces are just slightly greater than repulsive)
suspending agents can also be called….
viscosity inducing agents
how do suspending agents work to increase viscosity of the continuous medium
they form a film around the particles and decrease their attraction to each oter
name 5 suspending agents
explain structurally what they usually are
alginates
CMC
xanthan gum
tragacanth
acacia
long chain molecules or natural or synthetic powder gums
name 2 non ionic surfactants and what surfactants do in suspensions
span and tween
decrease the interfacial tension between the particles and the liquid
function of wetting agents in suspensions and name 2
glycerin and propylene glycol
to enhance the penetration of the vehicle into the drug particles. POWDER MUST BE WETTED to be formulated as suspension
**note - she may ask if something is a solution or suspension just from looking at ingredeitns - know what to look for
ie - suspending agent/wetting agent/surfactant for suspension
function of buffers in suspensions
what is normal pH
to resist pH changes and maintain the pH of the formulation
7.4-8.4
name 4 things that can be used as buffers in suspensions
carbonates
citrates
gluconates
phosphate salts
why are osmotic agents added to suspensions?
which particular suspensions are they usually added to?
name 4
opthalmic and injectable suspensions
to make osmotic pressure comparable to body fluids (isotonic)
dextrose, mannitol, sorbitol, glycerol
why are humectants added to suspensions and name 2
propylene glycol and glycerol
added to ASBORB MOISTURE to prevent the API from degrading
in solutions, co solvents are added to improve solubility of the drug
but what are cosolvents used for in the case of suspensions?
to enhance the viscosity of the dispersion medium – bc they have a high viscosity in themselves
glycerin, PPG, sorbitol
which preservatives are only effective at a low pH (less than 4) and are thus not used a lot for suspensions bc the ideal pH is 7.4-8.4?
benzoic acid and benzoic acid salts
why are parabens used in pairs as preservatives?
bc they show synergy
why are parabens very commonly used in suspensions?
bc effective at ph 4-8
**name the concentration of alcohol needed to preserve suspensions in:
-acidic media
-neutral/alkaline media
acidic - 15% alcohol
neutral/alkaline - 18% alcohol
combo of ___% methyl paraben and ___% propyl paraben is commonly used as preservative
0.18% methylparaben
0.02% propylparaben
so around .2% all together
explain the ideal packaging of suspensions
TIGHT CONTAINERS with big enough opening to pour viscous liquid
enough space to shake well
SHAKE WELL BEFORE USE STICKER
label should indicate if internal or external use
which USP chapter is stability considerations
USP1191
3 major signs of instability of suspensions
-cake
-ostwald ripening (large particles - excessive crystak growth)
-microbial contamination bc of free water
when compounding a suspension, if any of the solids are determined to to be soluble in the amount of vehicle prescribed, what should you do?
**
DO NOT WANT EVERYTHING TO DISSOLVE
just dissolve in PART OF the vehicle
**in compounding suspensions, what should be done with the INSOLUBLE powders
be placed in a mortar and triturated according to GEOMETRIC DILUTION
why is trituration necessary for suspensions but not solutions
solutions will dissolve anyway
***when wetting the insoluble powders that have been triturated according to geometric dilution, what should be done nect?
add just enough of an appropriate wetting agent (ie - glycerin) to make a THICK, SMOOTH PASTE – called a NUCLEUS
this removes air pockets
*once the powder has been wetted, what is done nect?
the vehicle is added in portions with suspending agent
thorough mixing after each addition
add most of the vehicle amount while the mixture is still in the mortar
then transfer to conical graduate and rinse mortar with remaining vehicle
QS, transfer to prescription bottle
SHAKE WELL BEFORE USE
when compounding a suspension, you notice that 1 of the ingredients is soluble in water
what do you do?
dissolve it in a PORTION of the water
whenever a liquid formulation calls for the use of a tablet or capsule, prepare it as a ________
why?
SUSPENSION
bc even if the API is soluble in water, there are so many other ingredients that are not
based on stokes, rate of sedimentation decreases if the viscosity of the external phase ________
increases
based on stokes equation, the rate of sedimentation decreases if the particle size of the internal pahse _________
decreases
