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Pharmaceutical Sciences > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Dispersed System

A

Mixture of one phase in another largely immiscible phase

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2
Q

What is another term for dispersed phase?

A

Internal phase

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3
Q

What is another term for external phase?

A

Continuous phase

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4
Q

Suspension

A

Solid particles dispersed in a liquid medium

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5
Q

Emulsion

A

Liquid droplets dispersed in a liquid medium

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6
Q

3 classifications of a dispersed system

A

Molecular, colloidal, coarse

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7
Q

Advantages of suspensions

A

Preparation of poorly soluble drugs, masks taste, easier to swallow, prepare oral, IV, topical

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8
Q

Disadvantages of suspensions

A

Instability, non-uniformity, bulkier

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9
Q

3 examples of suspensions

A

Insulin, magnesium hydroxide, penicillin G procaine

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10
Q

Suspendable

A

Drug substance is uniformly dispersed after shaking container

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11
Q

Re-dispersable

A

Settled solid phase is readily and uniformly dispersable

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12
Q

Desired physical properties of suspensions

A

Suspendable, re-dispersable, transferable, smooth/grit free

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13
Q

Physically stable

A

State of no aggregation and uniform distribution of particles

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14
Q

Interface

A

Boundary between existing phases

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15
Q

T/F every surface is an interface

A

True

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16
Q

If you increase the surface area, what happens to the free energy

A

increases

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17
Q

T/F Increased surface energy creates a stable system

A

False, thermodynamically unstable

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18
Q

Decreasing particle size causes what to increase?

A

Interfacial area

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19
Q

Agglomerate

A

Stick together

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20
Q

Why do you use wetting agents

A

Increase solubility and increase affinity to liquid to decrease agglomeration

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21
Q

Define wetting

A

Solid-air interface is changed to solid-liquid interface

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22
Q

Potential determining ions

A

Specifically absorbed ions that influence the surface charge

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23
Q

Stern layer

A

Tightly bound layer of solvent and counter ions on the solid surface

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24
Q

Surface potential

A

Electrical potential on the surface

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25
Q

What does the presence of counter ions do in the stern layer?

A

Shields solid surface charge and decreases electrical potential across the stern layer

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26
Q

Shear plane is also called

A

the slipping plane

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27
Q

Shear plane

A

Shell of solvent molecules and ions existing around each particle beyond the stern layer

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28
Q

Where is the zeta potential found

A

Shear plane

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29
Q

Zeta potential

A

Potential difference between the shear plane and the electrically neutral bulk medium

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30
Q

What does the zeta potential dictate

A

Magnitude of electrical repulsion

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31
Q

Major forces that suspended particles are subject to

A

Electrical double layer repulsion and Van der Waals attractive forces

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32
Q

Zeta potential has positive or negative energy of interaction

A

Positive

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33
Q

Van der Waals attractive forces have positive or negative energy of interaction

A

Negative

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34
Q

Where does attraction predominate

A

Small and large distance – Primary and secondary minimums

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35
Q

Where do electrical repulsions predominate

A

Intermediate distances – primary maximum

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36
Q

Flocculation

A

Easy to suspend particles

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37
Q

When is a secondary minimum not observed

A

High repulsive forces

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38
Q

When are flocs formed

A

At secondary minimum

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39
Q

What do high zeta potentials create

A

High repulsive forces; primary maximum

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40
Q

What happens when zeta potentials are very high

A

No secondary minimum, deflocculated suspension

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41
Q

When does coagulation occur

A

If particles overcome the repulsion barrier and approach primary minimum

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42
Q

Caking

A

Non dispersible hard sediment

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43
Q

Rheology

A

Study of the flow behavior of liquids and the deformation of solids

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44
Q

Viscosity

A

Resistance to flow

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45
Q

What is viscosity a measure of

A

Molecular friction that resists flow

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46
Q

Shear stress

A

Tangential force applied per unit area which produces flow

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47
Q

Rate of shear

A

change in velocity with distance

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48
Q

How do you find viscosity

A

Shear stress/rate of shear

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49
Q

Newtonian liquid

A

Rate of shear increases proportionally with shear stress, viscosity is constant

50
Q

Plastic flow

A

Not observed until minimum shearing stress is applied (Yield)

51
Q

What is exhibited below the yield value

A

Elastic behavior

52
Q

What happens above the yield value

A

newtonian behavior

53
Q

Pseudoplastic flow

A

No yield point, viscosity decreases with increase in shear stress

54
Q

Pseudoplastic is what kind of behavior

A

Shear thinning

55
Q

Dilatant flow

A

Rare, increase viscosity when increase rates of shear

56
Q

What kind of behavior does dilatant flow show

A

Shear thickening

57
Q

Stokes law

A

Rate of sedimentation of uniformly sized particles in dilute suspensions

58
Q

Deflocculated

A

Particles exist in suspension as separate particles, stays dispersed longer than flocculated, low sedimentation rate

59
Q

Flocculated system

A

Loose aggregates with high sedimentation rates

60
Q

Sedimentation volume ratio

A

Equilibrium volume/total volume, want to be 1 (Flocculation with no sediment)

61
Q

Degree of flocculation equation

A

Ultimate sediment volume of flocculated suspension/ultimate sediment volume of deflocculated suspension

62
Q

Degree of flocculation

A

Measure of the extent of increase in sediment volume achieved by flocculation

63
Q

What do surfactants do

A

Decrease interfacial tension, promote wetting of solids, facilitate dispersion

64
Q

3 types of flocculating agents

A

Electrolytes, surfactants, polymers

65
Q

Structured vehicle

A

Provides viscous medium to slow down sedimentation of suspended particles

66
Q

Clay vehicles

A

Provide a 3D network of interacting particles minimizing flocs

67
Q

Polymeric vehicles

A

Shear thinning properties make re-dispersion easier and minimize settling

68
Q

Organleptic additives

A

Aspects of a product that the patient experiences through the senses

69
Q

What can thickeners cause in formulations

A

Microbial growth

70
Q

Levigation

A

Triturating powders in a mortar or using a spatula on a tile with a small amount of liquid, reducing particle size and wetting the surface

71
Q

Gels

A

Semisolid systems containing gelling agents which are suspensions of small inorganic particles or polymer solutions

72
Q

Jellies

A

Gels with high water content in the matrix

73
Q

Gel network

A

Interlaced structure increasing the internal friction and provides resistance to flow

74
Q

4 gel structures

A

Randomm coils, helix, stacks, house of cards

75
Q

Random coils

A

Synthetic polymers such as cellulose derivatives

76
Q

Helix

A

Intertwined molecular chain structure such as xanthan gum

77
Q

Stacks

A

Cross linking of polymer chains by divalent cations

78
Q

House of cards

A

Alignment of positively charged edges with negatively charged flat surface of the particles

79
Q

Liquid phase gel classifications

A

Hydrogels and organogels

80
Q

Gel former/structure classifcation

A

Single phase and two phase

81
Q

Thixotropy

A

Breakdown of structure that does not re-form immediately when stress is removed

82
Q

How can gelling be induced

A

Gelling agent, pH, cross linking ions, thermal gelation

83
Q

Reversible thermogelation

A

Change in temperature causes viscosity to go one way, but alter returns

84
Q

Emulsion

A

Thermodynamically unstable mixture of two immiscible liquids with two phases stabilized by an emulsifier

85
Q

Two emulsion classifications

A

O/W, W/O

86
Q

Bancroft’s rule

A

The phase in which the emulsifier is more soluble constitutes the continuous phase

87
Q

Advantages of emulsions

A

Preparation of two immiscible liquids, administration of non-aqueous liquid phase, masks taste, improved bioavailability, IV administration with oil, external application

88
Q

Ideal Characteristics of emulsions

A

Constant, small droplet size, appropriate consistency, redispersible

89
Q

Physically stable

A

Product is where we want it, may be thermodynamically unstable

90
Q

If droplets of an emulsion coalesce, what happens

A

decrease in free energy, causes settling to be faster

91
Q

What causes cracking

A

Combination of creaming and coalescence

92
Q

Creaming

A

Oil droplets rise, increasing amount of droplets

93
Q

Emulsifying agents include

A

Surfactants, hydrated lyophilic colloids, auxiliary, finely divided solids

94
Q

What do surfactants do in emulsions

A

Create monomolecular films, reduce interfacial tension, facilitate breakdown of internal phase, prevent coalescence, creates repulsion

95
Q

What type of surfactant is not susceptible to pH change

A

Non ionic

96
Q

HLB value

A

Hydrophile lipophile balance, affinity for water and oil phase in non ionic surfactants

97
Q

High HLB

A

More soluble in water, o/w emulsion

98
Q

Low HLB

A

More soluble in oil, W/O emulsion

99
Q

Griffin method

A

Proportion between weight percentages of hydrophilic and lipophilic groups in non ionic surfactant molecule would dictate surfactant behavior

100
Q

Davies method

A

Sum of groups + 7

101
Q

What do hydrated lyophilic colloids do in emulsions

A

No effect on interfacial tension, form multi molecular films around droplets, creates stability when dissolved in external phase

102
Q

What do finely divided solid particles do in emulsions

A

Orient at interface and form coalescence barrier

103
Q

How do auxiliary emulsifiers function

A

Thicken or form gel structure to provide coalescence barrier

104
Q

Emulsion stabilization mechanisms

A

Repulsion due to like surface charges (Zeta), Tightly packed surfactant molecules to hinder coalescence, adsorbed polymer trans physically hinder, polymer strands form bridges, solid particles at interface hinder coalescence

105
Q

Destabilization of emulsions

A

Temperature changes, microbial growth, addition of chemical agents

106
Q

Semisolids

A

Viscous preparation that is not pourable and does not flow under low shear stress at room temperature but exhibits spreadability on skin and mucous membrane surfaces

107
Q

Uses of semisolids

A

Protect skin/mucous membrane, promote hydration, provide a vehicle

108
Q

Properties of topical products

A

Occlusive, humectant, emollient, protective

109
Q

Occlusive

A

Promotes retention of water by forming hydrophobic barrier that prevents evaporation of moisture from within skin

110
Q

Humectant

A

Causes water to be retained because of its hygroscopic properties

111
Q

Emollient

A

softens and reduces irritation

112
Q

Ointment

A

Semisolid preparation intended for external use containing less than 20% water

113
Q

Creams

A

Semisolid emulsion containing more than 20% water

114
Q

Pastes

A

Stiff ointments with high concentration of solid particles in fatty vehicle, more adherent when applied

115
Q

Types of ointment bases

A

oleaginous, absorption, water washable, water soluble

116
Q

Oleaginous bases

A

Emollient, occlusive, not water washable, hydrophobic, greasy

117
Q

Absorption base types

A

hydrophilic anhydrous or w/o emulsion

118
Q

Absorption base

A

Emollient and occlusive, greasy, can incorporate water

119
Q

Water washable bases

A

O/W, non occlusive, non greasy

120
Q

Water soluble base

A

Non greasy, non occlusive, cannot use on weeping skin, anhydrous, water washable

121
Q

Outermost layer of skin

A

Stratum corneum, major barrier for drug

122
Q

Transdermal routes

A

Transcellular, intercellular, transfollicular

Pharmaceutical Sciences (2 decks)

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