Section 4: Disperse Systems Flashcards
1
Q
In a disperse system, what is the dispersed substance known as?
A
Dispersed phase
2
Q
In a disperse system, what is the vehicle known as?
A
Continuous or dispersing phase
3
Q
What is a solid in a liquid called?
A
A suspension
4
Q
What is a liquid in a liquid called?
A
An emulsion
5
Q
What is a solid/liquid in air called?
A
An aerosol
6
Q
What does suspension mean by USP terms?
A
Dosage forms that are solid-liquid dispersions
7
Q
What are 4 other names for suspensions?
A
1) Milk
2) Magma
3) Lotion
4) Syrup
8
Q
What is an example of a suspension that is called a “milk”?
A
Milk of magnesia
9
Q
What is an example of a suspension that is called a “magma”?
A
Bentonite magma
10
Q
What is an example of a suspension that is called a “lotion”?
A
Hydrocortisone lotion
11
Q
What is an example of a suspension that is called a “syrup”?
A
Doxycycline syrup
12
Q
What are the USP guidelines for nomenclature of dosage forms?
A
Be named by route of administration (ex: oral, topical) and their physical system (ex: tablet, solution)
13
Q
What is an example of an old name that was changed to meet the requirements of USP nomenclature?
A
White lotion is now called zinc sulfide topical suspension USP
14
Q
What can define a dispersed system?
A
Particle size
15
Q
What are 2 characteristics of coarse dispersions?
A
1) Solute not dissolved completely and is visible
2) Size over 10 micrometers
16
Q
What are coarse dispersions generally used for?
A
Suspensions and emulsions
17
Q
What are 2 characteristics of fine dispersions?
A
1) Solute not completely dissolved
2) Size between 0.5 and 10 micrometers
18
Q
What are fine dispersions generally used for?
A
Magmas and gels
19
Q
What are 2 characteristics of colloidal dispersions?
A
1) Solute not completely dissolved, but not visible
2) Size between 1 nanometer and 0.5 micrometers
20
Q
What is a property of colloidal dispersions?
A
Will scatter light
21
Q
What are 2 characteristics of molecular solutions?
A
1) Solute completely dissolved in solvent
2) Size below 1 nanometer
22
Q
Do true molecular solutions scatter light?
A
No
23
Q
Disperse systems are thermodynamically ______
A
Unstable
24
Q
True or false: disperse systems are 1-phase systems
A
False, they are 2-phase systems
25
What does a larger particle size cause with respect to dispersion?
Larger particle = greater tendency to separate from the dispersing phase
26
____ tend to settle while _____ rise to the top
Solids; liquids
27
What is needed for dosing accuracy with disperse systems?
The dispersed phrase should be restored to uniform distribution throughout the dispersing phase with moderate agitation of the container
28
What are suspensions?
Two-phase systems of a finely divided solid uniformly dispersed in a liquid phase
29
What is the normal particle size for suspensions?
10-50 micrometers
30
For suspensions, what is the continuous phase usually?
Aqueous
31
For suspensions, how much solubility does the solute have in the continuous phase?
Minimal
32
What is often done to suspensions for oral use?
Sweetened or flavoured
33
What are suspensions for topical use called?
Lotions
34
What are 4 advantages to suspensions as a dosage form?
1) Easy to swallow
2) Flexibility in giving doses of different sizes
3) Able to mask disagreeable tastes
4) Drug may have increased stability
35
What are 3 disadvantages to suspensions as a dosage form?
1) Physically unstable and will separate over time
2) Dosing inaccuracy if homogeneity not restored before use
3) May have an unpleasant feeling in the mouth, especially if large particle size
36
What are 3 desirable attributes of a suspension?
1) Should settle slowly and be readily re-dispersed with gentle shaking
2) Particle size should remain fairly constant over the product's shelf-life
3) Should pour evenly and readily
37
What is a disperse system?
A liquid preparation containing undissolved or immiscible drug distribution throughout the vehicle
38
What are the 6 factors involved in Stokes law?
1) Rate of settling
2) Diameter of particles
3) Density of particle
4) Density of medium
5) Gravitational constant
6) Viscosity of the medium
39
What does Stokes :aw explain?
Rate of settling in a suspension
40
What 3 things does Stokes Law indicate?
1) Sedimentation is a function of particle size
2) Sedimentation is an inverse function of viscosity
3) Rate of sedimentation can be slowed by reducing the particle size and/or increasing the viscosity of the medium
41
With respect to Stokes Law, what does a small particle size mean?
Tendency for caking or agglomeration increases
42
What does agglomeration prevent?
Easy redispersion of settled particles
43
What is a way to prevent agglomeration?
Forming floccules
44
What are floccules?
A loose aggregation of particles
45
What holds floccules together?
Weak particle-particle bonds (van der Waals interactions)
46
What is a difference between flocculated and non-flocculated suspensions?
Flocculated suspensions form a higher sediment volume
47
What does the loose structure of flocculated suspensions allow for?
Easy redispersion
48
How can floccules be formed?
By adding a small quantity of surfactant (or sometimes electrolytes), which at specific concentrations may neutralize surface changes
49
What changes once floccules are formed?
Particle size becomes larger
50
What should be added because floccules have a larger particle size?
A viscosity-increasing agent
51
What does thixotropic mean?
- When a substance can switch between solid and liquid
| - Usually appears as solid when no pressure is applied, and behaves like a liquid when sufficient pressure is applied
52
What must be considered when turning a solid dose form into a liquid oral dose form?
Stability, bioavailability, preservative, flavour, and colour
53
What is the typical procedure when turning a solid dose form into a liquid oral dose form?
- Powder/empty the appropriate number of tablets/capsules
- Use a mortar and pestle and an appropriate levigating agent to prepare a smooth paste
- Add structured suspending vehicle in portions
- Make to volume, mix by inversion, and dispense into suitable bottle
54
What is an appropriate levigating agent when turning a solid dose form into a liquid oral dose form?
Glycerin
55
What is an appropriate vehicle when turning a solid dose form into a liquid oral dose form?
- A commercially-prepared one like Ora-Sweet
| - May also use syrup or a methylcellulose-type vehicle
56
What must be done when doing compounding for infants?
Minimize exposure to preservatives, alcohol, and propylene glycol
57
What is the go-to expiration for aqueous products as directed by the USP?
No more than 14 days in the fridge
58
When can an expiration date exceed 14 days?
With the use of preservatives
59
What is an emulsion?
A dispersion of small droplets of liquid in another immiscible liquid
60
What is the third phase of an emulsion?
Emulsifying agent
61
What kind of emulsion involves the continuous phase being aqueous?
Oil and water emulsion
62
What kind of emulsion involves the continuous phase being oleaginous?
Water and oil emulsion
63
What can emulsions be used for?
Oral, topical, parenteral, or ophthalmic
64
What are the most common emulsions?
Topical
65
What are very uncommon emulsions?
Oral
66
What is an advantage to water and oil emulsions?
More occlusive (air can't get through it when applied topically)
67
What is an advantage to oil and water emulsions?
Better drug release
68
What is an example of a water in oil emulsion for topical use?
Vaseline
69
What is a disadvantage to emulsions?
Physically unstable and will revert to 2 immiscible phases
70
What type of emulsion will cause droplets to rise to the top?
Oil and water
71
What type of emulsion will cause droplets to settle to the bottom?
Water and oil
72
**What can be done after creaming has occurred?
Re-disperse with shaking
73
**What is creaming?
When internal phase droplets merge and rise to top or settle to bottom
74
How can emulsions be stabilized?
Use of surfactants, hydrocolloids, or solid particles
75
What is a surfactant?
Hydrophilic or lipophilic portions of molecule that concentrate at oil:water interface
76
What do surfactants do?
Lower interfacial tension between phases which reduces repellant forces between them, and reduces attractive force within each phase
77
What does a surfactant facilitate?
Breaking of globules into smaller droplets
78
What are the 2 types of surfactants and what are 2 examples of each?
1) Anionic (sodium docusate, sodium oleate)
| 2) Non-ionic (Spans, Tweens)
79
What type of surfactants are rarely used and why?
Cationic because irritation and toxicity occurs in the amount required
80
What do hydrocolloids provide?
- Protective multi-molecule layers around dispersed droplets
| - May provide a charge which causes droplets to repel each other
81
What are the 3 types of hydrocolloids and what is an example of each?
1) Natural (gelatin)
2) Semi-synthetic (methylcellulose)
3) Synthetic (carbopols)
82
What happens to solid particles when mixed with droplets and what does this cause?
- Tend to form layer around droplet and swell
| - Increases viscosity and reduces attraction between droplets
83
What is the function of auxiliary agents?
Thicken
84
What are examples of auxiliary agents?
- Fatty acids
- Fatty alcohols
- Fatty esters
85
What is the hydrophilic-lipophilic balance?
A system designed to aid in determining type and amount of emulsifier needed to prepare stable emulsions
86
How are HLB values determined?
Experimentally
87
What is the scale for HLB values?
1-18
88
What does a low HLB value indicate?
Emulsifier is oil-soluble, so oil phase will predominate and a water and oil emulsion will form
89
What are HLB values assigned to?
Oils and oil-like materials
90
What is the equation for the HLB value of an emulsion?
(quantity surfactant 1)(HLB surfactant 1) + (quantity surfactant 2)(HLB surfactant 2) / (quantity surfactant 1 + quantity surfactant 2)
91
How are emulsions prepared in industry?
With large tanks and high-speed homogenizers or colloid mills
92
What must be put into the system to make an emulsion?
Energy
93
What are the 4 general methods for extemporaneous preparation of emulsions?
1) Continental
2) English
3) Bottle
4) Beaker
94
What is used in the continental method of preparing emulsions?
4 parts oil, 2 parts water, and 1 par emulsifier/gum
95
What is generally used as the gum in the continental method of preparing emulsions?
Acacia
96
What type of mortar and pestle is generally used in the continental method of preparing emulsions?
Porcelain
97
Describe the continental method of preparing an emulsion
- Acacia is levigated with the oil until they are thoroughly mixed
- Water is then added at once with vigorous trituration
- Additional solid materials are dissolved in some of the remaining water (if they are water soluble); oil-soluble material is dissolved in oil
- Preparation is transferred to a measuring cylinder and made to volume
98
What is the same and different between the english and continental methods of preparing emulsions?
- Same proportion of materials
| - Different order of mixing
99
Describe the english method of preparing an emulsion
- Gum is triturated with water to make a mucilage
| - Oil is added in portions with vigorous mixing
100
When would the bottle method for making an emulsion be used?
If oil has low viscosity
101
What is a similarity between the bottle and continental methods of preparing emulsions?
Same proportions of materials
102
Describe the bottle method of preparing an emulsion
- Acacia put into bottle, oil added, and vigorously mixed
| - Water is added and more vigorous mixing
103
Describe the beaker method of preparing an emulsion
- All water soluble materials are dissolved in water and all oil soluble materials are dissolved in oil using beakers
- Both solutions heated to about 70 C in a water bath
- Internal phase added to external phase with mixing
- Stirred until cooled
104
What does acacia contain?
Neutral sugars and acids
105
What is the continuum of dispersions?
From true solutions to coarse suspensions and emulsions
106
What is the stability of colloidal dispersions?
Relatively stable
107
What can colloidal dispersions consist of?
Single large molecule of high MW
108
What can colloidal dispersions appear as?
True solutions that scatter light
109
How is dispersion maintained in colloidal dispersions?
Brownian movement
110
What are colloidal dispersions effective at?
"Solubilizing" insoluble drugs
111
What are the 2 types of colloidal dispersions?
1) Lyophilic
| 2) Lyophobic
112
What does higher viscosity mean for colloidal dispersions?
Improved system stability because interaction between particles is reduced
113
What can cause a hydrophilic colloid to carry a surface charge?
- The pH of the system
| - Chemical functional groups of colloid
114
_____ keeps particles separated
Charge
115
What can neutralizing or changing the charge of particles cause?
Can cause them to attract each other and grow
116
Are hydrophilic systems stable or unstable and why?
- Quite stable
| - High affinity between particles and the continuous phase
117
Why are hydrophobic systems less stable than hydrophilic systems?
Hydrophobic systems have no interaction between colloid and continuous phase
118
What causes settling in hydrophobic colloids?
- Attraction then association between colloid particle
| - Addition of electrolyte that may neutralize the charge
119
How can a hydrophobic colloid be stabilized?
By developing some attraction between particles and continuous phase with surfactants or protective colloids that can coat the particle
120
What keeps a hydrophobic colloid dispersed?
Mutual repulsive forces and Brownian movement
121
What are gels?
Hydrophilic colloidal systems with high degree of cross-linking or association
122
Gels have high ____
Viscosity
123
Gels have _____ phase movement
Continuous
124
What is the normal concentration of a gelling agent?
0.5-2%
125
What kind of preparation is a gel?
A semi-solid preparation of small inorganic or large organic molecules interpenetrated by liquid
126
When would a gel be called a magma?
When particle size is large
127
What is a gel made of?
Discrete particles
128
A gel is ____-phase
Two
129
When is a gel single phase?
If large organic macromolecules are uniformly distributed with no apparent boundaries between dispersed and continuous
130
What is an example of a single phase gel?
Natural gums
131
What are gels useful for?
Preparing oral, topical, nasal, ophthalmic, and vaginal dose forms
132
What are the 4 types of classification systems for gels?
1) Inorganic
2) Organic
3) Hydrogels
4) Organogels
133
Jellies are ____ and contain ____
- Structurally conherent
| - Water and a thickening agent
134
What is a common problem in the preparation of gelling agents?
Wetting them
135
What are 4 examples of gelling agents?
1) Alginic acid
2) Bentonite or Vee gum
3) Carbomer
4) Poloxamer
136
What is carbomer compatible with?
Alcohol
137
What are disperse systems useful for?
Topical, oral, ophthalmic, and parenteral dose forms
138
What should be done before using disperse systems?
Shake them
139
What must the caregiver understand when giving a disperse system?
- Needs to be shaken
- Route
- Storage
140
What is the function of methylcellulose?
Suspending agent
141
What is the function of citric acid?
pH adjuster
142
What is the function of sodium benzoate?
Preservative
143
What is the function of aspartame?
Sweetener
144
What is the function of orange flavour?
Flavouring agent
145
What is the function of purified water?
Solvent
146
What is the function of tween 80?
Non-ionic surfactant
147
What is the function of span 20?
Non-ionic surfactant
148
What is the function of cherry syrup?
Vehicle
