Suspensions Part 2

Question 1

explain what flocs/flocculated suspensions are

Answer 1

particles are weakly bound together (called flocs) when the forces of attraction are just slightly greater than the repulsive forces

Question 2

true or false

flocculated suspensions rapidly undergo sedimentation

Answer 2

true

Question 3

are flocculated suspensions readily re-suspended?

Answer 3

YES

Question 4

flocculated suspensions have a______ sedimentation volume

Answer 4

large

Question 5

what is the appearance of the supernatant in flocculated suspensions

Answer 5

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

Question 6

_____ suspensions are also known as aggregated suspensions

Answer 6

DEflocculated

Question 7

do deflocculated suspensions settle fast or slow?

Answer 7

slow

Question 8

explain why and how deflocculated suspensions are not desirable

Answer 8

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

Question 9

true or false

deflocculated suspensions initially have a pleasant appearance

Answer 9

TRUE
they will remain cloudy for a while after shaking

BUT —– will eventually form a cake

Question 10

what is actually an advantage of deflocculated suspensions?

Answer 10

uniform dosing can be achieved – but only EARLY before the cake forms
this is bc the sedimentation occurs SLOWLY

Question 11

true or false

deflocculated suspensions have poor physical stability/quality

Answer 11

true

Question 12

in deflocculated/aggregated suspensions, explain the relationship between attractive and repulsive forces

Answer 12

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)

Question 13

suspending agents can also be called….

Answer 13

viscosity inducing agents

Question 14

how do suspending agents work to increase viscosity of the continuous medium

Answer 14

they form a film around the particles and decrease their attraction to each oter

Question 15

name 5 suspending agents

explain structurally what they usually are

Answer 15

alginates
CMC
xanthan gum
tragacanth
acacia

long chain molecules or natural or synthetic powder gums

Question 16

name 2 non ionic surfactants and what surfactants do in suspensions

Answer 16

span and tween

decrease the interfacial tension between the particles and the liquid

Question 17

function of wetting agents in suspensions and name 2

Answer 17

glycerin and propylene glycol

to enhance the penetration of the vehicle into the drug particles. POWDER MUST BE WETTED to be formulated as suspension

Question 18

**note - she may ask if something is a solution or suspension just from looking at ingredeitns - know what to look for

Answer 18

ie - suspending agent/wetting agent/surfactant for suspension

Question 19

function of buffers in suspensions

what is normal pH

Answer 19

to resist pH changes and maintain the pH of the formulation

7.4-8.4

Question 20

name 4 things that can be used as buffers in suspensions

Answer 20

carbonates
citrates
gluconates
phosphate salts

Question 21

why are osmotic agents added to suspensions?
which particular suspensions are they usually added to?

name 4

Answer 21

opthalmic and injectable suspensions

to make osmotic pressure comparable to body fluids (isotonic)

dextrose, mannitol, sorbitol, glycerol

Question 22

why are humectants added to suspensions and name 2

Answer 22

propylene glycol and glycerol

added to ASBORB MOISTURE to prevent the API from degrading

Question 23

in solutions, co solvents are added to improve solubility of the drug

but what are cosolvents used for in the case of suspensions?

Answer 23

to enhance the viscosity of the dispersion medium – bc they have a high viscosity in themselves

glycerin, PPG, sorbitol

Question 24

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?

Answer 24

benzoic acid and benzoic acid salts

Question 25

why are parabens used in pairs as preservatives?

Answer 25

bc they show synergy

Question 26

why are parabens very commonly used in suspensions?

Answer 26

bc effective at ph 4-8

Question 27

****name the concentration of alcohol needed to preserve suspensions in: -acidic media -neutral/alkaline media

Answer 27

acidic - 15% alcohol neutral/alkaline - 18% alcohol ************

Question 28

combo of ___% methyl paraben and ___% propyl paraben is commonly used as preservative

Answer 28

0.18% methylparaben 0.02% propylparaben so around .2% all together

Question 29

explain the ideal packaging of suspensions

Answer 29

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

Question 30

which USP chapter is stability considerations

Answer 30

USP1191

Question 31

3 major signs of instability of suspensions

Answer 31

-cake -ostwald ripening (large particles - excessive crystak growth) -microbial contamination bc of free water

Question 32

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? ********

Answer 32

DO NOT WANT EVERYTHING TO DISSOLVE just dissolve in PART OF the vehicle

Question 33

**in compounding suspensions, what should be done with the INSOLUBLE powders

Answer 33

be placed in a mortar and triturated according to GEOMETRIC DILUTION

Question 34

why is trituration necessary for suspensions but not solutions

Answer 34

solutions will dissolve anyway

Question 35

***when wetting the insoluble powders that have been triturated according to geometric dilution, what should be done nect?

Answer 35

add just enough of an appropriate wetting agent (ie - glycerin) to make a THICK, SMOOTH PASTE -- called a NUCLEUS this removes air pockets

Question 36

*once the powder has been wetted, what is done nect?

Answer 36

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

Question 37

when compounding a suspension, you notice that 1 of the ingredients is soluble in water what do you do?

Answer 37

dissolve it in a PORTION of the water

Question 38

whenever a liquid formulation calls for the use of a tablet or capsule, prepare it as a ________ why?

Answer 38

SUSPENSION bc even if the API is soluble in water, there are so many other ingredients that are not

Question 39

based on stokes, rate of sedimentation decreases if the viscosity of the external phase ________

Answer 39

increases

Question 40

based on stokes equation, the rate of sedimentation decreases if the particle size of the internal pahse _________

Answer 40

decreases