Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Pharmaceutics > Disperse Systems > Flashcards

Disperse Systems Flashcards

1
Q

what is a disperse system?

A

liquid preparation containing undissolved or immiscible drug dispersed through a vehicle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

which is the dispersed phase and which is the dispersing phase?

A 
dispersed = distributed substance
dispersing = vehicle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the difference between a suspension and an emulsion?

A

suspension: dispersed phase is a solid
emulsion: dispersed phase is a liquid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is the term for the disperse system when air is the vehicle?

A

aerosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the difference between a coarse dispersion and a fine/colloidal dispersion?

A

coarse: particle size is 10-50um

fine/colloidal: particle size 0.5-10um

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

give an example of a coarse dispersion and a fine/colloidal dispersion

A

coarse: suspensions, emulsions
fine: magmas, gels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what does particle size have to do with separation from vehicle?

A

the larger the particle size, the greater the tendency to separate from the dispersing medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is one important thing to do before using a disperse system?

A

shake well before use to distribute drug evenly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is a suspension?

A

two phase system consisting of a finely divided solid dispersed in a (usually aqueous) liquid phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the general oral use for suspensions? topical use?

A

oral: sweetened flavour formulations
topical: lotions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are 4 advantages to suspensions?

A

1) useful for pts who have difficulty swallowing tablets/capsules but the drug is insoluble
2) flexibility in giving doses
3) mask unpleasant taste
4) more stable than solutions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are 2 disadvantages to suspensions?

A

1) unstable (solids will settle over time leading to lack of uniformity)
2) possible unpleasant mouth-feel/texture (large particle size)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are 3 desirable attributes of a suspension?

A

1) suspension should settle slowly and be readily re-dispersed with gentle shaking
2) particle size should remain fairly constant over shelf life of the product
3) suspension should pour readily and evenly from its container

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is Stokes’ law?

A 
dx/dt = (d^2(pi-pe)g)/18n
dx/dt = rate of settling
d = particle diameter
pi = particle density
pe = medium density
g = gravitational constant
n = medium viscosity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does Stokes’ law indicate about rate of settling

A

rate of settling is a function of particle size (smaller particles settle slower) and inverse function of viscosity (more viscous solutions settle slower)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what could happen if particle size is too small?

A

caking may occur, and drug will not re-disperse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how do you prevent caking from occurring?

A

form a floccule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is a floccule?

A

loose aggregation of the particles held together by van der Waals forces, allowing for easy re-dispersion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How do you form a floccule?

A

Add a small amount of surfactant or electrolytes to neutralize the particle surface charges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Floccules usually settle faster, how do you prevent this?

A

add suspending agent to increase viscosity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what are 2 suspending agents?

A 
methylcellulose
polyvinylpyrrolidone (PVP)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what are 2 characteristics of a desirable suspension?

A

pseudoplastic

thixotropic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is considered low shear rate? high shear rate?

A

low: storage, just after shaking, while pouring
high: shaking

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what does thixotropic mean?

A

slow recovery from deformation (shaking), remaining in fluid long enough to be poured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what does pseudoplastic mean?

A

higher viscosity at lower shear rates and lower viscosity at higher shear rates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is extemporaneous compounding?

A

the preparation of a prescription drug in a pharmacy according to the given prescription

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what are two properties to keep in mind with extemporaneous compounding?

A

stability

bioavailability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what is the first step for extemporaneous compounding?

A

empty appropriate # of capsules/grind up tablets and add a small amount of vehicle/levigating agent to make smooth paste

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is the second step for extemporaneous compounding?

A

add vehicle with continuous mixing then add to graduated cylinder and bring to volume

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what preservatives should be avoided with infants and neonates? what does this mean in terms of expiry date?

A

alcohol
propylene glycol
expiry: short beyond use date (14 days) and require refrigeration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what is the expiry date for products containing preservatives?

A

25% of remaining expiration date of commercial product or 6mo. whichever comes first

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the process used for dry powders for oral suspensions?

A

must first loosen the powder then add the correct amount of solvent (usually water) accurately measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

what is an emulsion?

A

a dispersion in which the dispersed phase (internal phase) is composed of small droplets of liquid distributed throughout a vehicle, in which it is immiscible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the difference between oil in water (o/w) and water in oil (w/o) emulsions?

A

o/w: continuous phase is aqueous

w/o: continuous phase is oleaginous

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what dose forms could emulsions be used for?

A

oral
topical (most)
parenteral
ophthalmic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

why aren’t emulsions used for oral use very often?

A

poor patient acceptance (oily and unpalatable)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

when is it better to use a w/o topical emulsion? why?

A

on unbroken skin since it’s easier to apply as a thin film, softening on the skin (resists drying) and tends to be more occlusive/more difficult to remove.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

what is good about o/w topical emulsion?

A

less greasy feel
easier to remove with washing
small particle size of internal phase may promote better absorption of medication

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

what is creaming?

A

occurs when the dispersed internal phase droplets merge and rise to the top (o/w) or settle to the bottom (w/o) but can be re-dispersed by shaking

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

what is breaking or cracking?

A

occurs when the internal phase undergoes coalescence and there is complete and irreversible separation of the dispersed phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

what is one way to stabilize emulsions?

A

use of emulsifying agents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

what are some examples of emulsifying agents?

A

surfactants
hydrocolloids
solid particles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

whats an example of a cationic surfactant? anionic surfactant? non-ionic surfactant?

A

cationic: benzalkonium chloride
anionic: sodium docusate, sodium oleate
non-ionic: spans and tweens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

why are cationic surfactants rarely used?

A

irritating and potentially toxic in amounts required

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

what are examples of natural hydrocolloids? semi-synthetic? synthetic?

A

natural: acacia, gelatin
semi: methylcellulose
syn: carbopols

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

how do solid particles work as an emulsifying agent?

A

form a layer around the dispersed droplets and tend to swell in the dispersion medium to increase viscosity and reduce the attraction between the dispersed droplets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

what are some examples of solid particle emulsifying agents?

A

bentonite
aluminum hydroxide
magnesium trisilicate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

what are some examples of auxiliary emulsifying agents?

A 
fatty acids (stearic acid)
fatty alcohols (cetyl alcohol)
fatty esters (glyceryl monostearate)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

what is the function of the hydrophilic-lipophilic balance (HLB)?

A

aid in making decisions about the amount and types of emulsifying agents needed to form stable products

50
Q

how does the HLB work?

A

arbitrary scale of 1-18 assigned to emulsifying agents
low HLB: lower number of hydrophilic functional groups on the molecule (oil soluble) therefore oil phase will predominate (w/o)
high HLB: indicates water solubility, water phase will predominate (o/w)

51
Q

what is the HLB equation?

A

HLB = ((qty surfactant 1)(HLB surfactant 1) + (Qty surfactant 2)(HLB surfactant 2))/(qty surfactant 1 + qty surfactant 2)

52
Q

what are the 4 methods of emulsion preparation in a pharmacy?

A

1) continental method
2) english method
3) bottle method
4) beaker method

53
Q

what is usually in a primary emulsion for the continental method?

A

oil (4 parts)
water (2 parts)
hydrocolloid/gum-type emulsifier (1 part) - usually acacia

54
Q

how do you prepare the primary emulsion?

A

levigate the gum with 4 parts of oil until powder is thoroughly wetted, then 2 parts water added at once
mixture vigorously triturated until its creamy white and is viscous

55
Q

when are water soluble ingredients added to the primary emulsion? oil soluble?

A

water - after primary emulsion is prepared

oil - added to oil prior to making primary emulsion

56
Q

what occurs after the primary emulsion is made in the continental method?

A

transfer to a measuring cylinder and make to volume and shake to ensure uniform distribution

57
Q

what is the english method of preparing a primary emulsion?

A

use the same ratio, but the gum is triturated with the water and then the 4 parts oil is added in portions with vigorous trituration

58
Q

when can you use the bottle method?

A

when using oils of low viscosity

59
Q

how is an emulsion prepared using the bottle method?

A

same ratio, but gum is added to the bottle then oil is added and shaken
water is added next and shaken to mix

60
Q

in what case would you not use the 4:2:1 ratio for making emulsions? why? what method is this for?

A

when synthetic emulsifiers are used because a smaller amount of emulsifying agent is required
beaker method

61
Q

how does the beaker method work to prepare an emulsion?

A

oil soluble components are dissolved in the oil; water soluble components are dissolved in water.
both solutions heated to 70C in a water bath and then internal phase is added to the external phase with stirring until product reaches room temperature

62
Q

What is a colloidal dispersion?

A

those where the particle size ranges from 1nm to 1um

could be single large molecules of high MW or aggregates of smaller molecules

63
Q

how can you tell a colloidal dispersion from a true solution?

A

opaque particles scatter light when a beam of light is passed through at right angles (Tyndall effect)
true solution = no scattering

64
Q

how is uniform dispersion maintained in colloidal dispersions?

A

brownian movement (due to particles being bombarded by molecules of dispersing medium)

65
Q

what are the two types of colloids in regards to interaction with the solvent?

A

lyophilic - solvent loving

lyophobic - solvent hating

66
Q

what are hydrophilic molecules?

A

have an affinity for water and when dispersed in water, they become hydrated

67
Q

what happens with a hydrophilic molecule becomes hydrated?

A

they swell and increase the viscosity of the system

68
Q

what happens when the viscosity of a system is increased? why?

A

improvement in stability

reducing interaction between particles so there is less tendency for particles to coalesce, increase in size, and settle

69
Q

what charge do gums like acacia and methylcellulose possess? why?

A

negative

carboxylic and sulfate functional groups

70
Q

how can surface charge influence a colloidal dispersion?

A

presence of surface charge produces repulsion of particles and reduces the chance that the particles will adhere and settle (increase stability)

71
Q

what type of colloidal dispersions are usually made?

A

hydrophilic

72
Q

what happens when surfactant molecules are introduced in water?

A

form micelles

73
Q

which is more of a concern regarding stability: hydrophilic or hydrophobic colloids? why?

A

hydrophobic

no affinity between dispersed and continuous phases, meaning no change in viscosity occurs

74
Q

what are some examples of hydrophobic colloids? (5pts)

A 
oils
water-insoluble drugs
silver chloride
gold
sulfur
75
Q

how can you increase the stability for a hydrophobic colloid?

A

create some affinity between the particles and the continuous phase by using surfactants or protective colloids

76
Q

what may cause a hydrophobic molecules to carry an electric charge?

A

absorption of electrolyte ions from solution

77
Q

how can you neutralize the particle? what happens when you neutralize the particle?

A

addition of ions of opposite charge

neutralized particles will coalesce and precipitate

78
Q

what influence neutralization efficiency?

A

valence of the ion

79
Q

rank the following ions from most effective to least effective at neutralizing a negative charge?
Aluminum
Calcium
sodium

A

aluminum > Ca > Na

80
Q

what is the use of gelatin (hydrophilic colloid)?

A

add it to a hydrophobic colloid, and the gelatin is adsorbs onto the hydrophobic colloid and surround it, making it behave like a hydrophilic colloid (protects from electrolytes)

81
Q

what are some examples of colloidal systems in pharmacies?

A

vitamin K1
cyclosporine A
paclataxol
amphotericin-B injections

82
Q

what are gels? (2def’ns)

A

hydrophilic colloidal systems
semisolid systems consisting of suspensions made up of small inorganic particles/large organic molecules interpenetrated by a liquid

83
Q

how are gels made?

A

using agents which undergo a high degree of cross-linking or association when hydrated, increasing viscosity of the system

84
Q

what restricts movement of the dispersing phase?

A

interlacing 3D network of particles or solvating macromolecules

85
Q

what is the typical concentration range of gelling agents found in gel?

A

0.5-2%

86
Q

what is the difference between a gel and a magma?

A

gel: two phase system of small discrete particles
magma: relatively large particle size

87
Q

what do single-phase systems consist of?

A

organic macromolecules uniformly distributed through a liquid in such a manner that no apparent boundaries exist b/w the dispersed macromolecules and the liquid

88
Q

what is imbibition?

A

taking up of liquid without an increase in volume

89
Q

what is swelling?

A

taking up of liquid with an increase in volume

90
Q

what is syneresis?

A

when the interaction between particles of the dispersed phase increases on standing and the dispersing medium is squeezed out as droplets and the gel mass shrinks

91
Q

what is thixotropy?

A

reversible change from sol to gel

92
Q

what is a xerogel?

A

formed when a liquid is removed from the gel and only the framework remains

93
Q

what are some uses of gels?

A

preparing oral, topical, nasal, and ophthalmic and vaginal formulations

94
Q

what are the 4 main categories for gels?

A

inorganic
hydrogel
organic
organogel

95
Q

what is a main difference between organic and inorganic gels?

A

inorganic - two phase system

organic - one phase system

96
Q

give an example of an inorganic gel and an organic gel

A

inorganic - aluminum hydroxide gel, bentonite magma

organic - tragacanth, carbomer

97
Q

what is characteristic of the ingredients found in hydrogels?

A

ones dispersible as colloids or are soluble in water

98
Q

what kind of ingredients are found in organogels?

A

hydrocarbons like mineral oil hydrocarbon waxes
fats (lards, cocoa butter)
soap base greases (Al stearate)

99
Q

what are jellies?

A

gels in which the structurally coherent matrix contains water (with active drug) and a thickening agent

100
Q

what could be some thickening agents found in jellies?

A

tragacanth
gelatin
carboxymethylcellulose

101
Q

what are two ways of avoiding microbial growth in jellies?

A

antimicrobial preservative

stored in fridge

102
Q

how do you prevent evaporation of water in jellies?

A

stored in a closed container

103
Q

what is a problem with preparing gels (esp. organic polymers)?

A

wetting the powder
the powder usually forms clumps and the interior of the clump remains dry, taking a long time for the material to hydrate

104
Q

how do you overcome the problem with wetting the powder?

A

slowly adding the dry powder in portions with aggressive mixing to disperse the powder and allow the small particles to hydrate

105
Q

what is a second technique to overcome wetting the powder?

A

disperse powder in a medium in which it is insoluble and then add the dispersed powder to the solvent with mixing

106
Q

what are some examples of mediums that could be used to disperse the powder?

A

alcohol
glycerin
proplyene glycol

107
Q

what is alginic acid?

A

gelling agent obtained from seaweed

usually tasteless

108
Q

what concentration range is used for alginic acid?

A

1-5%

109
Q

what happens when soluble calcium salt is added to the dispersion with alginic acid?

A

cross-linking occurs and the product becomes much more viscous

110
Q

what is bentonite?

A

colloidal hydrated aluminum silicate which is insoluble in water but swells to ~12x its volume in water to form a gel

111
Q

what makes bentonite good to use in gels?

A

thixotropic
forms of a sol when shaken which allows easy and rapid dispersion of suspension particles and easy pouring for administration

112
Q

what is a bad thing about bentonite?

A

it is alkaline and may pose stability problems for an added medication
if it’s acidified, it loses its viscosity

113
Q

what can carbomer/carbopol resins be used for?

A

thickening, gelling, emulsifying or suspending agents

114
Q

what happens when a carbomer is added to an alkali?

A

neutralizes with the alkali and forms a very viscous product

115
Q

what can you neutralize aqueous dispersions with? hydroalcoholic dispersions?

A

aqueous - NaOH

hydro - triethanolamine

116
Q

what use is poloxamer at concentrations of 15-50% in water?

A

it forms gels which are stable in the presence of acids, alkalis and metal ions

117
Q

what name are poloxamers marketed under? what are they mainly used for?

A

Pluronic

used as topical drug delivery systems

118
Q

what auxiliary label should be on all disperse system containers?

A

shake well before use

119
Q

what can a pharmacist do to ensure proper shaking of the disperse system?

A

provide disperse system in oversized container so shaking can be effective

120
Q

what is the usual concentration of surfactants in a dispersion system?

A

5%

Pharmaceutics (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions