Suspensions

Question 1

Suspension

Answer 1

liquid preparations that consist of solid particles dispersed throughout a liquid phase

Question 2

Suspensions vs. Solutions

Answer 2

-takes time to dissolve
-zero order (degradation is independent of conc.)
-used for bitter drugs (since it takes time to dissolve)

Question 3

Suspensions vs Tablets

Answer 3

-has more dose flexibility
-easier to swallow
-good dissolution rate

Question 4

Desirable properties of suspensions

Answer 4

-should NOT settle rapidly
-when particles settle they should NOT form a hard cake
-readily dispersed
-easy to administer (balance of viscosity)
-particle size remains constant during storage (maintains dissolution rate)

Question 5

Settling

Answer 5

LARGE particles settle QUICKLY
if the difference of density is large then it SETTLES QUICKLY (solid is more dense)

Question 6

Stokes Law

Answer 6

if V is POSITIVE = settles quickly
if V is NEGATIVE = settles slowly

Question 7

What are the different types of suspensions?

Answer 7

-dispersed suspension
-flocculated suspension
-structured vehicle system

Question 8

Thermodynamic stability of suspensions?

Answer 8

-the most stable when delta G = 0
-get there through: aggregation and crystal growth

Question 9

Van der Waals attractive force

Answer 9

-happens in moderate distance of the molecules, stronger on the surface
-NOT AFFECTED by formulation

Question 10

Hydration repulsive force

Answer 10

-force generated by having a water layer on the particles (helps with repulsion)
-NOT AFFECTED by formulation

Question 11

Electrostatic repulsive force

Answer 11

-surface charge on the particles
-AFFECTED by formulation (pH or solution conditions)

Question 12

Steric repulsive force

Answer 12

-generated due to polymers on the surface of the particle
-AFFECTED by formulation (pH or solution conditions)

Question 13

Mechanism of Dispersed suspension

Answer 13

-make the repulsive forces dominant and they don’t aggregate
-although when they settle it forms a cake which is difficult to resuspend (due to high attractive forces)
-CLOUDY suspension, slow rate of suspension

Question 14

Mechanism of Controlled flocculation

Answer 14

-repulsive and attractive forces are in BALANCE
-attracted to each other at the secondary minimum
-produce a sediment at high volume when they settle
-easy to redisperse
-rapid rate of sedimentation
-clear supernantant

Question 15

Types of flocculating agents

Answer 15

-clay (bentonite magma)
-alternation of pH
-reduce the electrical barrier b/t particles
-nonionic or ionic surfactants

Question 16

Structured vehicle system

Answer 16

-purpose is to thicken the dispersion medium and suspend particles
-shouldn’t affect the bioavailability
-shouldn’t make it too viscous
-appear as semi-solid when undisturbed but fluid when shaken
-no sedimentation

Question 17

Examples of structured vehicle system

Answer 17

carboxymethylcellulose (CMC), methycellulose, microcrystalline cellulose, polyvinylpyrrolidone, xanthan gum, bentonite, magnesium aluminum silicate

Question 18

Rheology

Answer 18

the study of flow characteristics

Question 19

Shear rate

Answer 19

how FAR the liquid will go given a force

Question 20

Shear stress

Answer 20

how much FORCE is applied

Question 21

Types of Rheology flows

Answer 21

-newtonian flow
-plastic (non-newtonian flow)
-pseudoplastic (non-newtonian flow)
-dilatant (non-newtonian flow)

Question 22

Newtonian flow

Answer 22

-ex: water
-graph is straight and linear
-viscosity graph is a straight horizontal line

Question 23

Plastic non-newtonian flow

Answer 23

-graph is characterized by yield value
-viscosity decreases when shear rate increases (shear thinning)

Question 24

Pseudoplastic non-newtonian flow

Answer 24

-graph is linearish with a slight curve, no yield value
-viscosity decreases when shear rate increases (shear thinning)

Question 25

Dilatant non-newtonian flow

Answer 25

-literally the opposite trend of the other flows
-viscosity increases as shear rate increases (shear-thickening)

Question 26

Thixotropy

Answer 26

the ability of a system that was disturbed to return to its undisturbed structure

Question 27

What flows show thixotropy?

Answer 27

plastic and pseudoplastic

Question 28

Wetting

Answer 28

displacement of air from the surface of a particle

Question 29

Mechanism of wetting

Answer 29

reduce the surface tension of the aqueous vehicle to allow water to enter the pore and displace air

Question 30

Examples of wetting agents

Answer 30

polysorbate 80 (tween 80) bc it’s hydrophilic