PSII Exam II

Question 1

Define a dispersed system

Answer 1

A mixture of one phase in another largely immiscible phase.

Question 2

Define a suspension

Answer 2

Solid particles dispersed in a liquid medium.

Question 3

Define an emulsion

Answer 3

Liquid droplets dispersed in a liquid medium.

Question 4

Define a molecular dispersion

Answer 4

A true solution; particle size less than 1 nanometer.

Question 5

Define a colloidal dispersion

Answer 5

Particle size less than half a micron.

Question 6

Define a coarse dispersion

Answer 6

Particle size greater than half a micron.

Question 7

What are three important stability characteristics of PHARMACEUTICAL dispersed systems?

Answer 7

1. Uniform distribution
2. Aggregation rate controlled.
3. Flocculation controlled.

Question 8

What are three fundamental physical chemistry concepts for PHARMACEUTICAL dispersed systems?

Answer 8

1. Interfacial properties
2. Vehicle viscosity
3. Dispersed particle properties

Question 9

What are two (2) mechanisms to impart stability common to pharmaceutical dispersed systems?

Answer 9

1. Repulsion of particles due to surface charge (zeta potential) [Electrical Barrier]
2. Physical hindrance by surfactant. [Mechanical Barrier]

Question 10

What are three (3) de-stabilization mechanisms for a pharmaceutical dispersed system?

Answer 10

1. Temperature changes (solubility, freezing)
2. Microbial growth (degredation)
3. Addition of chemical agents (pH-solubility, ionic strength).

Question 11

What are two ways to assess a suspension?

Answer 11

1. SEDIMENTATION VOLUME, F (ratio of final sedimentation height and original height -> magnitude increases as sediment height increases [due to greater # of settled particles].
2. DEGREE OF FLOCCULATION, Beta (ratio of flocculated height to unflocculated height -> magnitude increases as sediment height increases [due to greater space between particles].

Question 12

According to Stokes Law, what are two methods for decreasing the rate of settling (velocity of creaming)?

Answer 12

1. Decrease mean particle diameter. At

Question 13

What are two methods for increasing the degree of flocculation?

Answer 13

1. Electrolyte interaction with shear plane (affecting zeta potential).
2. Mechanical barrier with polymer or surfactant. (Requires optimal concentration for ‘bridging’)

Question 14

What are three (3) useful characteristics of surfactants?

Answer 14

1. Decrease interfacial tension
2. Promote wetting of solids
3. Facilitate dispersion

Question 15

Define a Newtonian liquid

Answer 15

Viscosity stays constant. Therefore, rate of shear increases proportionally to shear stress.

Question 16

What are three (3) classes of Non-Newtonian rheology?

Answer 16

1. Plastic flow
2. Pseudoplastic flow
3. Dilatant Flow

Question 17

Define plastic flow behavior

Answer 17

1. Below yield value, system exhibits elastic behavior.

2. Above yield value, system exhibits Newtonian behavior.

Question 18

Define pseudoplastic flow behavior

Answer 18

Viscosity decreases with increase in shear stress – shear-thinning behavior.

Question 19

Define dilatant flow behavior

Answer 19

1. Viscosity increases with increase in shear stress – shear-thickening behavior.

Question 20

Define thixotropy

Answer 20

Thixotropy is related to the time-dependent restoration of structure following shear stress for shear-thinning systems.

Question 21

How is thixotropy useful in pharmaceutical formulations?

Answer 21

Example: Shaking a nasal spray before use allows delivery into nasal cavity; viscosity recovery prolongs residence.

Question 22

What kinds of mechanical barriers can emulsifying agents form?

Answer 22

1. Monomolecular films
2. Polymolecular films
3. Adsorbed solid particles

Question 23

What is a necessary chemical property for an emulsifying agent to be effective?

Answer 23

It must have an affinity for both phases so that it is active at the interface.

Question 24

Describe the hydrophilic-lipothilic balance (HLB)

Answer 24

Scale of 1-60 that defines relative affinity for water and oil.

Question 25

What is the HLB value of a lipophilic emulsifying agent?

Answer 25

1-10

Question 26

What is the HLB value of a hydrophilic emulsifying agent?

Answer 26

>10

Question 27

What is Bancroft's Rule?

Answer 27

The phase in which an emulsifying agent has the greater affinity constitutes the continuous phase.

Question 28

Discuss two (2) important considerations when combining emulsifying agents.

Answer 28

1. The 'effective' HLB is a weighted average of agents. | 2. Structural characteristics (e.g. double bond) may result in incompatibility.

Question 29

Define a pharmaceutical gel

Answer 29

Semisolid system consisting of a condensed mass (matrix) enclosing a liquid.

Question 30

Define a jelly

Answer 30

A gel in which the matrix contains a high water content.

Question 31

Give two (2) examples of a single phase gel

Answer 31

1. Carbomer | 2. Hypromellose

Question 32

What is a hydrogel?

Answer 32

Liquid phase is water -- gel network is inorganic or organic

Question 33

Give three (3) examples of organic hydrogels

Answer 33

1. Carbomer 2. Poloxamer 3. Sodium carboxymethylcellulose

Question 34

What are four (4) types of structures seen in a gel matrix?

Answer 34

1. Random coils 2. Helix 3. Stacks 4. 'House of Cards'

Question 35

What are four (4) factors related to gel formation?

Answer 35

1. Gelling agent concentration 2. Solution pH 3. Ion cross-linkage 4. Thermal gelation

Question 36

Give an example of a gel formed with ion cross-linkage

Answer 36

Calcium alginate gels are formed with Ca2+ and Sodium Alginate.

Question 37

Give an example of a gel formed with solution pH

Answer 37

Carbopol gels are ionized (pKa 5-6) and electrostatic repulsion results in a gel network forming.

Question 38

Give an example of a gel formed with thermal gelation

Answer 38

Poloxamer is dehydrated at increased temperatures to form micelles which aggregate to form a gel network.

Question 39

What is a special consideration when using hydrogels of cellulose derivatives?

Answer 39

Levigation is required to help wet the clumped polymer when added to water..

Question 40

What is a special consideration when using sodium carboxymethylcellulose?

Answer 40

Optimal viscosity for NaCMC is observed at pH 7-9.

Question 41

Define an ointment

Answer 41

Semisolid preparation intended for external use. API is dissolved, suspended or emulsified.

Question 42

What are the four (4) USP classifications of ointment bases?

Answer 42

1. Hydrocarbon (oleaginous) -- oily with limited aqueous. 2. Absorption -- oily with enhanced aqueous. 3. Water removable -- oil in water emulsions. 4. Water soluble -- only water components.

Question 43

Define a cream

Answer 43

A semisolid emulsion.

Question 44

Define a paste

Answer 44

A semisolid with a large solid concentration.

Question 45

Give two (2) examples of oleaginous bases

Answer 45

1. 95% petrolatum + 5% wax | 2. Liquid petrolatum with low density polyethylene resin.

Question 46

Give three (3) examples of an absorption base

Answer 46

1. Aquaphor -- a commercially refined hydrophilic petrolatum. 2. Nivea Cream 3. Eucerin

Question 47

Give three (3) examples of water-washable bases

Answer 47

1. Dermabase 2. Cetaphil 3. Aquaphilic

Question 48

Give an example of a water-soluble base

Answer 48

Polybase

Question 49

What are four (4) characteristics of ointment bases?

Answer 49

1. Composition 2. Occlusiveness 3. Incorporation of API 4. Feel and Washability

Question 50

Characterize hydrocarbon (oleaginous) bases (4 components)

Answer 50

1. Composed of oily compounds 2. Occlusive 3. Incorporates hydrophobic API 4. Greasy, non-washable

Question 51

Characterize absorption (anhydrous) bases (4 components)

Answer 51

1. Composed of oily base + w/o emulsifier 2. Occlusive 3. Incorporates hydrophobic and small amounts of hydrophilic 4. Greasy, non-washable

Question 52

Characterize water-washable bases (4 components)

Answer 52

1. Composed of oil + water + o/w surfactant 2. Non-occlusive 3. Solids and small amount of aqueous solution -- poor hydrophobic. 4. Non-greasy and washable.

Question 53

Characterize water-soluble bases (4 components)

Answer 53

1. Water soluble ingredients 2. Non-occlusive 3. Solids and aqueous solutions 4. Non-greasy and washable.

Question 54

What are two (2) methods of preparing suppositories?

Answer 54

1. Hand-rolling | 2. Fusion molding

Question 55

Why are dosage calculations required for preparing drug-filled suppositories with fusion molding?

Answer 55

Components are measured by weight but dosage unit (suppository mold) is created by volume.

Question 56

Define Density Displacement Factor (DDF)

Answer 56

The weight of a drug in gram required to displace 1 g of base.

Question 57

What three (3) pieces of information are necessary to calculate a DDF?

Answer 57

1. Weight of blank suppository. 2. Weight of medicated suppository. 3. Weight of drug per suppository.