Test 3-Dispersed systems (suspensions and emulstions)

Question 1

Dispersed phase

Answer 1

solid drug particles

Question 2

Continuous phase

Answer 2

liquid (usually aqueous)

Question 3

Suspensions

Answer 3

-dispersions with insoluble particles that are dispersed in a liquid
-most are coarse dispersions with particles less than 5 micrometers
-colloidal suspensions with particles between 1nm and 5 micrometer are possible
-used to formulate insoluble or poorly soluble drugs
-drug is at a concentration above its solubility limit, hence why the drug won’t fully dissolve to form a solution

Question 4

oral suspension

Answer 4

already prepared as a suspension

Question 5

for oral suspension

Answer 5

contains powder to be reconstituted

Question 6

injectable suspension

Answer 6

intended for parenteral injection that is already prepared

Question 7

for injectable suspension

Answer 7

contains dry solids that upon addition of solvent form injectable suspensions

Question 8

Why create a suspension dosage form?

Answer 8

1. solubility limitations
2. stability concerns
3. mask taste
4. achieve sustained drug release

Question 9

Ideal properties of suspensions

Answer 9

-suspension should remain uniform during shaking and measuring of dose
-the particles that settle upon storage must be easily resuspended
-proper viscosity to pour freely from bottle or to push through a syringe needle
-if reconstitution is required, powder should be easily wetted

Question 10

Disadvantages with suspensions

Answer 10

-problems with wetting
-problems with caking

Question 11

Problems with wetting

Answer 11

-hydrophobic solid will trap air on its surface rather than allow the hydrophilic solvent to spread on the solid surface

Question 12

Problems with caking

Answer 12

-particles that have settled due to gravity aggregate to reduce surface exposed to continuous phase and become sufficiently dense (caked) that the particles cannot be redispersed

Question 13

Wetting agents

Answer 13

reduce the surface tension between a liquid and a solid helping to improve wettability

Question 14

Common wetting agents

Answer 14

-surfactants (tweens and spans)
-cosolvents (glycerin and alcohol)

Question 15

caking is influenced by….

Answer 15

-charge of the particles
-rate of sedimentation

Question 16

Most suspension particles have a surface charge.
Acidic functional groups will produce a _________ charged surface. Basic functional groups will produce a _________ charged surface

Answer 16

-negatively
-positively

Question 17

Zeta potential

Answer 17

a parameter that measures the electric charge at a particles surface

Question 18

Stokes equation

Answer 18

describes sedimentation of coarse dispersions

Question 19

To decrease velocity of sedimentation

Answer 19

• decrease particle size
• increase density of continuous phase
• increase viscosity of continuous phase

Question 20

Strategies to prevent caking

Answer 20

• add flocculating agents to create a flocculated suspension
• add density and/or viscosity enhancers to slow sedimentation rate

Question 21

Types of flocculating agents

Answer 21

• hydrophilic polymers
• polyvalent electrolytes
• surfactants

Question 22

Flocculation with hydrophilic polymers

Answer 22

-create bridges between the drug particles
-bridges are broken by shaking and reformed at rest

Question 23

Flocculation with polyvalent electrolytes

Answer 23

• particles with a surface charge attracted to opposite charge
• addition of ions with opposite charge of the net zeta potential will help in the formation of loose flocs
• e.g. sodium acetate, mono-, di-, trisodium phosphate, mono-, di-, trisodium citrate

Question 24

Flocculation with surfactants

Answer 24

• will localize on the surface of drug
• reduce the surface energy and neutralize charges on the surface of the particle
• at very high concentrations of surfactant, surfactant will completely surround particle within micelle and produce a deflocculated suspension
• e.g. lecithin

Question 25

excipients added to a vehicle to increase desity include:

Answer 25

• sugars like dextrose or sucrose
• glycerin, polyethylene glycol

Question 26

Suspending agents

Answer 26

• excipients added to a vehicle to modify viscosity
• will modify the flow of the suspension and often create pseudoplastic flow

Question 27

Examples of suspending agents

Answer 27

• hydrophilic polymers (methylcellulose, acacia, gelatin)

Question 28

Structured vehicle

Answer 28

when suspending agents are used in a vehicle

Question 29

Emulsions

Answer 29

coarse dispersions of two immiscible liquids (usually oil and water)

Question 30

Two types of emulsions

Answer 30

• oil is dispersed in a water continuous phase
• water is dispersed in a oil continuous phase

Question 31

Emulsions are commonly formulated for these routes of administration

Answer 31

• topical (o/w and w/o… lotions, creams, ointments)
• IV (o/w ….. propofol)

Question 32

Ideal properties of emulsions

Answer 32

• should remain homogenous during storage
• proper viscosity for intended use (i.e. to squeeze easily from an ointment tube)
• dispersed particles should be small and uniform
• for topical products, minimization of greasy feel

Question 33

Stability issues with emulsions

Answer 33

• creaming
• coalescence
• phase separation
• phase inversion

Question 34

3 types of emulsifying agents

Answer 34

• surfactants
• hydrophilic polymers (film-forming polymers)
• solid particulate film formers

Question 35

Types of surfactants

Answer 35

• anionic
• cationic
• nonionic
• Zwitterionic