Lecture 13/14

Question 1

suspensions

Answer 1

liquid preparations that consist of solid particles dispersed throughout a liquid phase in which the particles are not soluble
example - pepto bismol

Question 2

bismuth subsalicylate

Answer 2

active ingredient in pepto bismol
insoluble salt of salicylic acid linked to bismuth cation

Question 3

suspension vs solution - chemical stability

Answer 3

solution - first order (log graph)
suspension - zero order (constant graph)

Question 4

suspension vs solution?

Answer 4

due to solubility, chemical stability, and taste (oral suspension of erythromycin takes better than solution)
less excretion by suspension

Question 5

suspension vs tablets?

Answer 5

due to flexibility of dose, ease of swallowing, and faster dissolution rate

Question 6

components of suspension

Answer 6

flocculating agent, structured vehicle system, and wetting agent – different
also - active ingredient, vehicle, buffer, preservative, antifoaming agent, and flavor/sweetener

Question 7

desirable properties of suspensions

Answer 7

does not settle rapidly
not hard cake at the bottom from the particles
easy to administer (not too viscous or easily flowable through syringe)(fluid enough to spread over external area but not so mobile it slides off)
particle size remains constant during storage

Question 8

settling

Answer 8

stoke’s law
measured in cm/sec
sulfadiazine in water - 54 seconds to settle 1cm
microcrystalline sulfadiazine - 90min to settle 1cm
sorbitol solution as vehicle for microcrystalline sulfadiazine - 17 days to settle 1 cm

Question 9

stoke’s law equation

Answer 9

V (cm/sec, velocity of sedimentation)

d^2(diameter of particle in cm) x
Ps(density of solid) - Pl (density of liquid) x
980 (gravity constant)
/
18
n (viscosity of liquid)

Question 10

particle size

Answer 10

1-50 mcm
micropulverization, fluid energy grinding, and spray drying

Question 11

micropulverization

Answer 11

10 to 50 mcm
most oral and topical suspensions
high speed attrition or impact mills

Question 12

fluid energy grinding

Answer 12

under 10 mcm
parenteral or ophthalmic suspensions
jet milling, micronizing
shearing action of high-velocity compressed airstreams on the particles in a confided space

Question 13

spray drying

Answer 13

under 5 mcm
dryer – a cone-shaped apparatus into which a solution of a drug is sprayed and rapidly dried by a current of warm, dry air circulating in the cone

Question 14

suspension formulation designs

Answer 14

dispersed phase (solid particles)
dispersion medium

Question 15

types of suspensions

Answer 15

dispersed suspension
flocculated suspension
structured vehicle system

Question 16

thermodynamic stability equation

Answer 16

change in G (increase in surface free energy)

Ys/l (interfacial tension between solid and liquid) x
change in A (increase in surface area)

Question 17

thermodynamic stability

Answer 17

a suspension is stable when change of G is equal to 0
can never be reached in a suspesnion because we usually want small particles (high deltaA) for rapid dissolution
moves towards deltaG = 0 overtime due to processes that reduce deltaA

Question 18

processes that reduce the surface area

Answer 18

aggregation and crystal growth (increases particle size)

Question 19

Van der Waals attractive force

Answer 19

operates at moderate distance from the surface but becomes very strong close to the surface
formulation factors do not affect it

Question 20

hydration repulsive force

Answer 20

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

Question 21

electrostatic repulsive force

Answer 21

due to surface charge on the particles
could be controlled by the formulation

Question 22

steric repulsive force

Answer 22

due to an adsorbed layer of neutral polymer at the surface of a particle
may be controlled by the formulation

Question 23

repulsive force

Answer 23

+
comes closer to 0 from the top to the bottom

Question 24

attractive force

Answer 24

-
comes closer to 0 from the bottom to the top

Question 25

dispersed suspension

Answer 25

make repulsive forces dominant particle repel each other and do not aggregate problem - particles settle as individual particles leading to a cake sediment that can be difficult to resuspend

Question 26

controlled flocculation

Answer 26

repulsive and attractive forces are in balance particles are attracted to each other at the secondary minimum to form aggregates (known as floccules), which settle to produce a sediment with a high volume easy to redisperse settles fast, but less prone to compaction so breaks up easier

Question 27

sediment volume (f)

Answer 27

= final volume of sediment / volume of suspension

Question 28

degree of flocculation (b)

Answer 28

= sediment volume of test suspension / sediment volume of dispersed suspension

Question 29

flocculating agents

Answer 29

clay (diluted bentonite magma) -- oral suspension alteration in the pH of the suspension -- parenteral solution electrolytes -- reduce the electrical barrier between the particles non-ionic or ionic surface-active agents

Question 30

suspension settles too rapidly

Answer 30

hinders accurate measurement of dosage esthetically not good

Question 31

structured vehicle

Answer 31

thicken the dispersion medium and help suspend particles should not interfere with availability of the drug should not make the suspension too viscous to agitate or to pour examples - polymer and clay

Question 32

rheology

Answer 32

study of flow characteristics shear rate (dv/dr) -- difference of velocity (dv) between two planes of liquid separated by a distance (dr) shear stress (F) -- the force per unit area, F'/A, required to bring about the flow newtonian vs non-newtonian flow

Question 33

non-newtonian flow

Answer 33

plastic - not fully exponential or constant (mix) pseudoplastic -- exponential dilatant -- logarithmic graph

Question 34

newtonian flow

Answer 34

F = F'/A = visocity(shear rate)

Question 35

plastic non-newtonian flow

Answer 35

typical of flocculated suspensions f (yield value) - threshold of shear stress necessary to initiate flow, represent the strength of the attractive force of the secondary minimum shear-thinning

Question 36

pseudoplastic

Answer 36

typical of polymer solutions such as methyl cellulose, etc shear-thinning

Question 37

dilatant

Answer 37

exhibited by suspension having a high solids content shear-thickening

Question 38

thixtropy

Answer 38

the ability of a system that was disturbed by an applied shear stress to return to its undisturbed structure plastic and pseudoplastic (shear thinning) fluids show it at rest, a gel will stabilize the suspension

Question 39

dispersed suspension approach

Answer 39

aim to achieve very slow rate of sedimentation cloudy suspension dense sediment may form non-suspendable sediment stoke's law

Question 40

controlled flocculation approach

Answer 40

rapid rate of sedimentation clear supernatant large sediment volume easily redispersed by shaking

Question 41

structured vehicle approach

Answer 41

may appear as a semi-solid when undisturbed but is fluid when shaken no sedimentation thixotropic

Question 42

wetting

Answer 42

displacement of air from the surface of a particle by the vehicle consider water-based (aqueous) vehicle consider hydrophilicity (like water) or hydrophobicity (dislike water) of the drug particles

Question 43

contact angle

Answer 43

a high contact angle indicates poor spreading and that cohesive forces of the liquid is strong hydrophilic - less than 90 degrees hydrophobic - greater than 90 degrees

Question 44

wetting agent

Answer 44

surface-active agent added to reduce the surface tension example - tween 80 used when the particles float as a result of pores filled with air not water