Suspensions Flashcards
suspensions are ____ phase systems:
2 phase
finely divided solid dispersed in a liquid medium
a pharmaceutical suspension is a ____ dispersion in which the internal phase is dispersed uniformly throughout the external phase
COARSE
solute is greater than 1 micron
(usually in compounding it’s around 400microns, and for commercial suspension it’s 3 microns)
how is the internal phase of insoluble solid particles maintained uniformly throughout the suspending vehicle??
1 or more suspending agents
true or false
suspensions are better at overcoming disagreeable taste than solutions
TRUE
which has faster rate of absorption - suspension or solution?
SOLUTION
True or false
some drugs are chemically unstable in solution but stable when suspended
TRUE
true or false
suspensions are only given by oral route
FALSE
can be externally applied or parenteral (ie - IM injection)
differentiate between dilute vs concentrated suspensions
dilute - 2-10% w/v of solid
concentrated - 50%w/v solid
how can suspensions be classified based on the proportion of solid particles
dilute or concentrated suspensions
3 ways suspensions can be classified by the SIZE of the solid particles
colloidal suspension (less than 1 micron)
coarse suspension (for compounded - 400 microns, for commercial ~3 microns)
nano suspension - 100-200nm
how can suspensions be classified based on the electro-kinetic nature of the particles
flocculated and deflocculated
name the 2 forms that suspensions are available in
ready to use suspensions and dry powder for suspension
how can you tell if a suspension is ready to use or a dry powder for suspension just by looking at the label?
“FOR ORAL SUSPENSION” indicates it is a dry powder for suspension
as recap, alcohol limits by age
less than 6 yrs old = <0.5%
6-12 yrs = <5%
children greater than 12yrs = <10%
true or false
essences and spirits cannot be given to pediatrics
TRUE
3 reasons why alcohol content limited for pediatrics
can alter liver function
cause gastric irritation
affect neurological depression
true or false
suspensions are not thermodynamically stable
TRUE
this is a disadvantage
bc of physical instability, they tend to settle over time and have lack of uniformity when dosing - MUST SHAKE WELL BEFORE USE
which are more CHEMICALLY stable - drugs in solution or drugs in suspension?
suspension
true or false
***drugs in suspension exhibit faster rate of absorption than many other dosage forms
TRUE
***rank the following by rate of absorption
capsule
coated tablet
suspension
compressed tablet
solution
FASTEST - solution
suspension
capsule
compressed tablet
SLOWEST - coated tablet
true or false
suspensions can mask the bad taste of a drug
TRUE
true or false
suspensions cannot be given as IM injections of depot therapy
FALSE - they can
true or false
a disadvantage of suspensions is that they are difficult to formulate
TRUE
bc they need wetting agent, suspending agent, etc
true or false
uniform and accurate dosing is easy to achieve with suspensions, and this is an advantage
FALSE
hard to achieve (UNLESS they are packed in unit dosing)
a disadvantage of suspensions is that they may be unpleasant to patients why?
bc of the texture
true or false
suspensions are bulky and hard to handle and transport
true
_____ viscosity for suspensions enhances physical stability
how?
HIGH
bc the particles settle slower
name the 2 types of flow
newtonian flow and non-newtonian flow
name the types of newtonian/non-newtonian fluids
newtonian - water/ethanol/olive oil/etc
non-newtonian - plastic flow/pseudoplastic flow/dilatant flow
most pharmaceutical fluids (IE - suspensions, emulsions, and gels) exhibit what flow
NONNEWTONIAN FLOW - PSEUDOPLASTIC
differentiate between what newtonian vs non-newtonian flow means
for NEWTONIAN fluids, viscosity will NOT change but will move when you heat it
for NONNEWTONIAN FLUIDS - the viscosity varies with the rate of sheer
“shear stress-dependent flow”
newtonian or non-newtonian
NON NEWTONIAN
Bingham flow is also known as…
plastic flow
explain how plastic (bingham) flow works
the bingham bodies do NOT begin to flow until a shearing stress (corresponding to the YIELD VALUE) has been exceeded
-have to shake well enough in order for flow (movement) to occur
what are bingham bodies vs liquids
substances that have a YIELD VALUE as solids
yield value must be met before flow
liquids will flow at the smallest yielding stress and have NO yield value
why does a “yield value” exist for plastic flow
bc of the van der waals forces holding the flocculated particles together
-these forces must be broken down before flow can occur!
the more flocculated the suspension, the _____ the yield value
HIGHER
true or false
if a product has a very high yield value, it will run easily
FALSE - low yield value will run easily
what flow is “shear-thinning system”
pseudoplastic flow
explain what pseudoplastic flow is
is it desired?
YES - ideal flocculated suspension exhibits pseudoplastic flow
as you give more and more shearing stress, the slope increases and the molecules move faster and faster until it becomes thin and runny. the long chain molecules will line up in 1 direction to move really fast
______ behavior is important for topical products
why?
pseudoplastic
when the viscosity decreases with stress, makes it easier to squeeze the product out of the container and to rub the product on large area of skin
in pseudoplastic flow, the long chain molecules (when put under stress) line up in what direction?
the direction of the flow
makes thin and runnt
what kind of flow is “shear-thickening systems”
is it desired?
dilatant flow
NOT ideal for suspensions. it’s the opposite of pseudoplastic flow
thickens and moves LESS as you apply more and more stress
_______ pharmaceutical materials may solidify under the conditions of high shear, damaging the equipment
DILATANT
ie - pushing IM injection - the suspension will thicken with the stress and not come out
when sheared, dilatant suspensions ______ in volume
increase
when the stress on a solidified dilatant system is REMOVED, what happens?
the suspension returns to its original state of fluidity
what is Ostwald ripening
suspensions that have a HIGH PERCENTAGE of dispersed solids will have an increase in resistance to flow as the rate of shear increases – WILL GET BIGGER
true for dilatant suspension
example of a household product that exhibits dilatant/shear-thickening flow
whipped cream
explain how with increasing rate of shear, whipped cream begins to thicken and get larger
(dilatant flow)
the insoluble proteins/globules will introduce AIR POCKETS
Explain what thixotropy is
when you don’t touch it, it will become thick and viscous – a gel like semisolid
however, once you shake, it will flow and become runny to be easy to pour.
when you let it sit again, it will regain viscosity but TAKES TIME TO REGAIN!!!!! this is time-dependent thixotropy. don’t want it to gain viscosity too quickly
name 2 routes of administration that thixotropic suspensions and emulsions can be used for and why
IM injections and nasal sprays
IM injections - when the drug passes the needle, it will break down in thickness and produce a DEPOT at the muscle, resulting in sustained release action
nasal spray (ie - nasonex) - SHAKE WELL BEFORE USE. this will allow it to flow more freely to spray. when it thickens in the nasal cavity, it wont leak out and is able to stay there longer
what is the name of the law involved with the sedimentation of suspended particles
STOKES LAW
to DELAY sedimentation according to stokes law, what should the particle size be?
as small as possible
as density of the liquid medium INCREASES, sedimentation rate _____
decreases
when is the sedimentation rate zero?
when the density of the medium is equal to the density of the solid
as the viscosity of the dispersion medium decreases, what happens to sedimentation rate?
it increases
true or false
it is desirable for suspensions to have very rapid sedimentation
FALSE
true or false
trituration is not necessary for suspensions
FALSE - IT IS
we want the particle size to be as small as possible to limit the rate of sedimentation
optional for SOLUTIONS bc it will dissolve either way
“particles should be easily redispersed on gentle shaking and regain viscosity SLOWLY”
thixotropy
throughout long periods of undisturbed standing of suspensions, what should happen to the particle size
should remain CONSTANT
true or false
it is desirable to have no grittiness in pharmaceutical suspensions
TRUE
also why we must triturate
it’s important for suspensions to have a balance between ___ and ____
stability vs pourability
should pour readily and evenly, but not be too watery
_____ suspensions should be sterilizable
parenteral/ophthalmic
which have longer (higher) shelf lives and WHY - commercial suspensions or compounded suspensions?
commercial suspensions because they have a much smaller particle size than compounded suspensions and are thus more stable
