exam 1 lecture 3

Question 1

suspensions

Answer 1

liquid preparations that consist of solid particles in liquid phase

Question 2

suspensions vs solutions
reasons for suspensions

Answer 2

solubility
chemical stability –> solution: first order, suspension: zero order
palatability –> erythromycin estolate oral suspension more palatable than solution

Question 3

suspensions vs tabs
reasons for suspensions

Answer 3

flexibility of dose
ease of swallowing
dissolution rate

Question 4

components of suspension

Answer 4

API
vehicle
buffer
preservative
flocculating agent
structured vehicle system
wetting agent
antifoaming agent
flavor + sweetener

Question 5

desirable properties

Answer 5

suspended material should not settle rapidly
particles that settle should not form hard cake, but be able to redisperse
ease of administration: not too viscous for pouring. lotions should be fluid enough to disperse
particle size remain constant during storage

Question 6

stokes law

Answer 6

V = (d^2 * (ps-pl) * 980) / (18*n)

Question 7

particle size

Answer 7

1-50 um
micropulverization: high speed attrition or impact mills (topical + oral 10-50 um)
fluid energy grinding: shearing action of high velocity compressed airstrear (<10um, parenteral + ophthalmic)
spray drying: solution is sprayed and rapidly dried by air. (< 5um)

Question 8

bring ∆G to zero

Answer 8

reduce surface area (∆A) + increase particle size
aggregation
crystal growth

Question 9

van der waals attactive force

Answer 9

operates moderate distance from surface but becomes very strong close to surface
formulation factors do not effect

Question 10

hydration repulsive force

Answer 10

due to absorbed water molecules at surface of a particle
formulation factors do not affect

Question 11

electrostatic repulsive force

Answer 11

surface charge on particles
may be controlled by formulation

Question 12

steric repulsive force

Answer 12

due to absorbed layer of neutral polymer at surface of particle
may be controlled by formulation

Question 13

dispersed suspension

Answer 13

make repulsive force dominant
particles do repel eachother and do not aggregate
problem: particles settle and can lead to cake

Question 14

controlled flocculation

Answer 14

repulsive + attractive force in balance
particles attracted to each other at secondary minimum to form aggregates (floccules)
floccules settle to produce a sediment w/ high volume
this sediment is easy to disperse

Question 15

dispersion

Answer 15

settles to form compact cake that is difficult to break up

Question 16

flocculation

Answer 16

settles fast but less prone to compaction, breaks up easily

Question 17

sediment volume (F)

Answer 17

volume of sediment / volume of suspension

Question 18

degree of flocculation

Answer 18

sediment volume of test suspension / sediment volume of dispersed suspension

Question 19

flocculating agents

Answer 19

clay - oral suspension
alteration in pH of suspension - parenteral solution
electrolytes - reduce barrier between particles
non-ionic or ionic surface-active agents

Question 20

structured vehicle system

Answer 20

semi-solid when undisturbed, but fluid when shaken
thicken dispersion medium and help suspend particles
- polymer: CMC, methylcellulose, microcrystalline cellulose, xanthan gum
- clay: bentonite, magnesium aluminum sillicate
should not interfere with availability of drug
should not make suspension too viscous to agitate or pour

Question 21

rheology

Answer 21

study of flow characteristics
shear rate - difference in velocity between two plans of liquid seperated by distance (dr)
shear stress - harder the stress, quicker the liquid flows

Question 22

newtonian flow

Answer 22

linear relationship between shear stress and rate of shear

Question 23

non-newtonian flow

Answer 23

non-linear relationship between shear stress and shear rate
plastic
pseudoplastic
dilatant

Question 24

plastic

Answer 24

flocculating suspensions
needs threshold to initiate flow
“shear thinning”

Question 25

psuedoplastic

Answer 25

CMC, methylcellulose
needs a lesser threshold to flow
latex paint

Question 26

dilatant

Answer 26

shear thickening
higher the force, less flow
cornstarch + water

Question 27

wetting

Answer 27

wet particle to remove air from surface of a particle by vehicle

Question 28

wetting agent

Answer 28

if solid has rough surface with many small pore, aqueous vehicle may not be able to enter the pores
best solution is to reduce surface tension
use surfactant like polysorbate 80