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Pharmaceutics > Feb 9 - Disperse Systems > Flashcards

Feb 9 - Disperse Systems Flashcards

1
Q

What is the difference between solution dose forms and disperse systems?

A

Solution dose forms are thermodynamically stable, one phase systems.
Disperse systems are thermodynamically unstable, two phase systems

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2
Q

What is a disperse system?

A

A disperse system refers to liquid preparations containing undissolved or immiscible drug distributed throughout the vehicle. The dispersed substance is known as the dispersed phase and the vehicle is known as the continuous dispering phase

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3
Q

What is a solid in a liquid?

A

A suspension

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4
Q

What is a liquid in a liquid?

A

An emulsion

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5
Q

What is a solid or liquid in air?

A

An aerosol

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6
Q

What other terms have historically been used as names for suspensions

A

Milk (e.g., milk of magnesia)
Magma (e.g., bentonite magma)
Lotion (e.g., hydrocortisone lotion
Syrup (e.g., doxycycline syrup)

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7
Q

Particle size may define a dispersed system. Name the four groups of dispersed systems defined by particle size

A

Coarse dispersions
Fine dispersions
Colloidal dispersions
Molecular solutions

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8
Q

Describe coarse dispersions

A

Solute not dissolved completely and is visible
Size > 10um
Suspensions and emulsions

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9
Q

Describe fine dispersions

A

Solute not completely dissolved
Size 0.5-10 um
Magmas and gels

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10
Q

Describe colloidal dispersions

A

Solute not completely dissolved but not visible
Size 1nm-0.5um
Will scatter light

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11
Q

Describe molecular solutions

A

Solute completely dissolved in solvent
True solutions do not scatter light
Size <1nm

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12
Q

Disperse systems are thermodynamically unstable systems. Explain

A

The larger the particle size, the greater the tendency to separate from dispersing phase
Solids tend to settle while liquids rise to the top
For dosing accuracy, the dispersed phase should be restored to uniform distribution throughout the dispersing phase with moderate agitation of the container

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13
Q

What are suspensions?

A

Two phase systems of finely divided solid uniformly dispersed in a liquid phase

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14
Q

Describe the characteristics of suspensions?

A

Particle size 10-50 um (or larger)
Continuous phase is usually aqueous and solute has minimal solubility in it
Suspensions may be sweetened and flavored for oral use
Suspensions for topical use may be called lotions

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15
Q

What are the advantages of suspensions as a dose form?

A

Ease of swallowing for patients who cannot swallow solid dose forms
Flexibility in giving doses of different size
Disagreeable taste may be masked
Drug may have increased stability

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16
Q

What are the disadvantages of suspensions as a dose form?

A

Physically unstable and will separate over time
If homogeneity not restored before use dosing inaccuracy will result
Patient may not like mouth-feel of product especially if particle size is relatively large

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17
Q

What are desirable attributes of a suspension?

A

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

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18
Q

What does Stoke’s law define?

A

The rate of settling in a suspension

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19
Q

What factors are involved in the rate of settling?

A 
The diameter of the particles
The density of the particle
The density of the medium
The gravitational constant
The viscosity of the medium (inversely proportionate; the more viscous the solutions settle more slowly)
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20
Q

How does reducing particle size affect the rate of sedimentation?

A

The rate of sedimentation will decrease

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21
Q

How does increasing the viscosity of the medium affect the rate of sedimentation?

A

The rate of sedimentation will decrease

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22
Q

What happens if the particle size is very small?

A

If particle size is very small, there may be a tendency of caking or agglomeration. This prevents easy redispersion of settled particles. Forming floccules is a way to prevent caking

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23
Q

What are floccules?

A

They are a loose aggregation of particles

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24
Q

Why is the formulation of floccules sometimes a useful strategy?

A

They are held together by weak particle-particle bones (van der Waals)
They form higher sediment volume than non-flocculated suspension
They are loose structure allows easy redispersion
They may form floccules by adding a small quantity of surfactant or sometimes electrolytes which at specific concentrations may neutralize surface charges

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25
Q

What should be done because of flocculation?

A

Because particle size with floccules are now larger, need to add a viscosity-increasing agent. Should rheologically be pseudoplastic - higher viscosity at low shear rates (storage, just after shaking, pouring) low viscosity at high shear rate (shaking)

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26
Q

What is extemporaneous compounding?

A

Product available only as a solid oral dose form can be a problem for elderly and children. A liquid oral dose form can be prepared but must consider stability and bioavailability. Also consider preservative, flavor, and colour

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27
Q

What is the typical procedure for extemporaneous compounding?

A

Typical procedure is to powder/empty appropriate number of tablets/capsules
Using a mortar and pestel and an appropriate levigating agent like glycerin, prepare a smooth paste
Add structured suspending vehicle in portions and add to measuring cylinder
Make to volume, mix by inversion and dispense into a suitable bottle

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28
Q

What’s the best vehicle to use for extemporaneous compounding?

A

Best to use commercially-prepared vehicle like Ora-Sweet
May use syrup or methylcellulose-type vehicle but must consider addition of preservative
With inflants and neonates, must minimize exposure to preservatives, alcohol and propylene glycol

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29
Q

When do extemporaneously compounded products expire?

A

Without published stability information, USP directs that expiration date for aqueous product no more than 14 days in the refrigerator

30
Q

Describe dry powders for oral suspension

A

Some commercial preparations like antibiotics supplied as dry powders or granules
Contain medication and excipient
Before dispensing, loosen powder and measure correct volume of purified water USP and add in portions to prepare suspension

31
Q

Constituents of suspensions or structured vehicle may contain what?

A

Active ingredient, wetting agent, suspending agent, flocculating agent, protective colloid, sweetener, preservative, buffer system, colour agent, flavour agent, antifoaming agent

32
Q

What are emulsions?

A

Dispersions of small droplets of liquid in another immiscible liquid. Emulsifying agent often a third phase. If continuous phase is aqueous, it’s called an oil-in-water (o/w) emulsion. If the continuous phase is oleaginous, it’s called a water-in-oil (w/o) emulsion

33
Q

Emulsion are used for what route of administration

A

May be oral, topical, parenteral, ophthalmic. Most are topical. Not common for oral use. Topical may be o/w or w/o and medication usually in internal phase. W/o are more occlusive; o/w are better for drug release

34
Q

What is creaming?

A

Emulsions are physically unstable and will revert to two immiscible phases. Creaming is when the internal phase droplets merge and rise to the top (o/w) or settle to the bottom (w/o). After creaming has occured, the emulsion can be redispersed with shaking.

35
Q

What is breaking/cracking?

A

Breaking or cracking occurs when the internal phase undergoes coalescence and there is a complete
and irreversible separation of the dispersed phase

36
Q

How are emulsions stabilized?

A

Emulsions may be stabilized through the use of surfactants, hydrocolloids or solid particles

37
Q

What are surfactants?

A

Hydrophilic and lipophilic portions of molecule and concentrate at oil:water surface. They lower the interfacial tension between phases which reduces repellant forces between them and reduces attractive forces within each phase. This facilitates breaking of globules into smaller droplets. Surfactants may be anionic (sodium docusate, sodium oleate) or non-ionic (Spans and Tweens). Cationic (quaternary ammonium halides) seldom used due to irritation and toxicity in amount required

38
Q

What are hydrocolloids?

A

They provide protective multi-molecule layers around dispersed droplets. They may provide a charge which causes droplets to repel each other. They may swell to increase viscosity of the system. Hydrocolloids may be natural (gelatin), semi-synthetic (methylcellulose) or synthetic (carbopols)

39
Q

What are solid particles?

A

They tend to form a layer around droplets and swell. This increases viscosity and reduces attraction between droplets. Agents include: bentonite, aluminum hydroxide, magnesium trisilicate

40
Q

What are auxiliary agents?

A

Occasionally an auxiliary agent may be used. They are not emulsifying agents and they tend to thicken. They include fatty acids (stearic acid), fatty alcohols (cetyl alcohol) and fatty esters (glyceryl monostearate)

41
Q

What is hydrophilic-lipophilic balance (HLB)?

A

A system designed to aid in determining the type and amount of emulsifier needed to prepare stable emulsions. HLB values can be experimentally determined and on a scale of 1 to 18. Low HLB values indicate emulsifier oil-soluble so oil phase will predominate and w/o emulsion will form. HLB values are also assigned to oils and oil-like materials. Select a blend of emulsifying agents with HLB value close to that of the oil phase

42
Q

Name four methods used to put energy into the system

A

Homogenization
High-speed sheer
Trituration
Agitation

43
Q

Name four general methods for extemporaneous preparation

A

Continental
English
Bottle
Beaker

44
Q

Describe the continental method for extemporaneous preparation

A

Primary emulsion from oil (4 parts), water (2 parts), hydrocolloid or gum emulsifier (1 part). Acacia is generally used as gum and porcelain mortar and pestle. The acacia is levigated with the oil until they are thoroughly mixed and then the water is added all at once with vigorous trituration. Additional solid materials are dissolved in some of the remaining water if they are soluble; oil soluble material would have been dissolved in the oil. Preparation transferred to a measuring cylinder and made to volume then mixed

45
Q

Describe the english method for extemporaneous preparation

A

Proportion of materials for the primary emulsion are the same but the order of mixing is different. The gum is triturated with water to make a mucilage then the oil is added in portions with vigorous mixing

46
Q

Describe the bottole method for extemporaneous preparation

A

Works best if oil has low viscosity. Same proportions of oil, water and gum (1:2:4). Acacia is put into the bottle, oil is added and vigorously mixed then water and vigorous mixing. Method can also refer to mixture of lime water and oil as it forms an in situ soap

47
Q

Describe the beaker method for extemporaneous preparation

A

With synthetic emulsifiers only about 5% is needed.. All the water soluble materials are dissolved in the water and all the oil soluble materials dissolved in the oil using beakers. Both solutions heated to about 70ºC on a water bath. Internal phase added to the external phase with mixing and stirred until cooled to room temperature. Sometimes hand-held blender or homogenizer helpful

48
Q

Describe colloidal dispersions

A

Dispersions may be classified by particle size; forms a continuum from true solutions to coarse suspensions and emulsions. Colloidal dispersions where particle size from 1 nm to 1 um. May consist of single large molecules of high molecular weight. May appear as true solutions but scatter light (Tyndall effect). Dispersions maintained by Brownian movement. Can be a method of ‘solubilizing’ insoluble drugs

49
Q

What is lyophobic/lyophilic?

A

Lyophobic means solvent-hating. lyophilic means solvent-loving. They are considered hydrophobic or hydrophilic when the continous phase is water

50
Q

Describe hydrophilic molecules

A

Hydrophilic molecules have affinity for water, hydrate and swell to increase viscosity. Higher viscosity improves system stability by reducing interaction between particles. They may carry a surface charge depending on pH of the system and chemical functional groups of the colloid. Charge keeps particles separated. Hydrophilic systems are quite stable with affinity between particles and the continous phase

51
Q

Describe hydrophobic molecules

A

Because there is no interaction between the colloid and continuous phase, they are less stable than hydrophilic molecules. Attraction then association between colloidal particle can cause settling. They can stabilize by developing some attraction between particles and continuous phase with surfactants or protective colloids like gelatin which can coat the particle. Some hydrophobic colloids may carry a charge or adsorb ions from the solution. Mutual repulsive forces and Brownian movement then keep colloid dispersed. Addition of electrolyte may neutralize charge and cause settling (like flocculation)

52
Q

Describe gels

A

Usually hydrophilic colloidal systems with a high degree of cross-linking or association. High viscosity and continuous phase movement restricted by three dimensional network of solvated macromolecules. Concentration of gelling agent 0.5-2%. Gel is a semi-solid preparation of small inorganic or large organic molecules interpenetrated by liquid. Gels are usefuly for preparing oral, topical, nasal, ophthalmic and vaginal dose forms

53
Q

Describe a large particle gel

A

If particle size is large it is called a magma (e.g., bentonite magma NF).

54
Q

Describe a discrete particle gel

A

If the gel is made is discrete particles is referred to as two-phase.

55
Q

Describe a single phase gel

A

A gel is considered single phase if large organic macromolecules uniformly distributed with no apparent bounderies between dispersed and continuous phase. Single phase systems may be made using natural gums (tragacanth, acacia, xanthan, carrageenan)

56
Q

Name the different classification systems for gels

A

Inorganic or organic

Hydrogels and organogels

57
Q

Describe jellies

A

Jellies are structurally coherent and contain water and a thickening agent. Drug is usually dissolved in the water prior to adding the thickening agent. Subject to microbial growth so should be preserved. Often need protection to prevent drying out

58
Q

Describe gelling agents

A

Problem during preparation of gels is wetting the powder. If the powder lumps, it is very difficult to disperse and hydrate. To solve this, add the powder in portions with vigorous mixing. Another technique is disperse the powder in a medium in which it is insoluble, then add the dispersed powder to the solvent with mixing. In some situations, levigation may be helpful

59
Q

What are some gelling agents?

A

Alginic acid
Bentonite or Vee Gum (magnesium aluminum silicate)
Carbomer (carbopol) - alcohol compatible
Poloxamer (15-50% concentration)

60
Q

What are disperse systems used for?

A

Useful for topical, oral, ophthalmic and parenteral dose forms. Most require shaking before use so need appropriate auxiliary label and caregiver should understand why this is important. Often packaged in oversized containers to facilitate shaking. Important that caregiver understand the route (e.g., oral antibiotics). May require other auxiliary labels: external use, refrigerate, etc. Caregiver must understand storage as well as route

61
Q

What is the function of hydrochlorothiazide?

A

Active pharmaceutical ingredient

62
Q

What is the function of methylcellulose?

A

Suspending agent

63
Q

What is the function of citric acid?

A

pH adjuster

64
Q

What is the function of sodium benzoate?

A

Preservative

65
Q

What is the function of aspartame?

A

Sweetener

66
Q

What is the function of orange flavor?

A

Flavoring agent

67
Q

What is the function of purified water?

A

Solvent

68
Q

What is the function of castor oil?

A

Active pharmaceutical ingredient

69
Q

What is the function of Tween 80?

A

Non-ionic surfactant

70
Q

What is the function of Span 20?

A

Non-ionic surfactant

71
Q

What is the function of cherry syrup?

A

Vehicle

Pharmaceutics (8 decks)

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