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PHAR 124 > Colloids > Flashcards

Colloids Flashcards

1
Q

What is the difference between colloids and suspensions?

A

Colloids:
- small
-filtration possible
-do not settle
Suspensions:
-large size
-filtration possible
-always settle

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2
Q

What are gelling agents?

A

Pharmaceutical excipient employed in making gels
Capable of undergoing high degree of cross-linking and entanglement in dispersion medium

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3
Q

Do gelling agents increase or decrease viscosity of gelling agent?

A

Increase

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4
Q

What is a two-phase system gelling agent?

A

Mostly inorganic gels - tendency to cross-link and solidify upon standing and liquify under stress like shaking

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5
Q

What is a one-phase system gelling agent?

A

Common gels in pharmacy - linear or branched polymer macromolecules that dissolve in water are used as gelling agents

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6
Q

What is the usual concentration of gelling agents?

A

0.5-5%
Some up to 10%

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7
Q

What are the types of gelling agents?

A

Natural polymers
Semi-synthetic polymers
Synthetic polymers

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8
Q

examples of natural polymers

A

Acacia, alginic acid and tragacanth

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9
Q

Examples of semi-synthetic polymers

A

Cellulose derivatives like methylcellulose

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10
Q

Examples of synthetics polymers

A

Carbomers or polaxamers

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11
Q

Higher gelling agent = _____

A

Stiffer (more viscous) gel

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12
Q

Alginic acid is obtained from____

A

Seaweed

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13
Q

What strength of gels is alginic acid used in and how long does it take to disperse in water?

A

1-5% and 30 minutes

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14
Q

What is the strength of sodium alginate?

A

10%

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15
Q

What must be added to alginic acid?

A

Preservatives because they are prone to microbial growth

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16
Q

Tragacanth is used for gels that are stable at pH ____

A

4-8

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17
Q

Tragacanth requires addition of ______

A

Preservatives

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18
Q

How do we prevent lumps from forming for powdered tragacanth in water?

A

Aqueous dispersions are prepared or wetting agents like glycerin are used

19
Q

At what pH do semi-synthetic agents maintain viscosity?

A

3-11
EXCEPT carboxylmethyl cellulose - 7-9

20
Q

What kind of gels does methylcullulose make?

A

Thinner gels

21
Q

What does methylcellulose have a high tolerance for?

A

Added drugs and salts

22
Q

Methylcellulose has good compatibility with _____

A

Water, alcohol and propylene glycol

23
Q

What does cooling Methylcellulose for an hour do?

A

Improves clarity and viscosity

24
Q

What kind of gels does hydroxypropylmethyl cellulose(HPMC) make?

A

Thicker gels

25
Q

What is HPMC compatible with?

A

Water and alcohol

26
Q

HPMC disperses good in _____

A

Cool water

27
Q

What is HPMC a good gelling agent for?

A

Time release preparations

28
Q

What are carbomers?

A

High bulk density and forms acidic aqueous solutions (pH 3)

29
Q

At what pH do carbomers thicken?

A

5-6, and become 1000x original volume

30
Q

For carbomers:
When dispersed - solution of pH is ____ - ______ to increase pH- _____ viscosity

A

Low
Neutralizer
Increase

31
Q

What are poloxamers?

A

Copopolymers of polyethylene and polyoxypropylene
It is an absorption enhancing topical gel

32
Q

What is poloxamer gel base widely used for?

A

Extemporaneous compounding

33
Q

What do poloxamers form?

A

Reverse thermal gels (dissolve in cold water or by cooling overnight)

34
Q

What concentration are poloxamers used in?

A

15-50%

35
Q

When are gels low viscosity and high viscosity?

A

Low temp = liquids (low viscosity)
High temp = gels (high viscosity)

36
Q

What is PLO gel?

A

Poloxamer combined with lecithin and isopropyl palmitate

37
Q

What is the most common compound made in a pharmacy using PLO gel?

A

Diclofenac 10%

38
Q

For PLO gel what is the aqueous phase and the organic phase?

A

Aqueous phase = pluronic
Organic phase = lecithin

39
Q

How does clumping occur in the preparation of gels?

A

Too rapid addition without adequate mixing
Outer molecule of the gelling agent contact the medium first
They hydrate forming a layer with the gelled surface that is difficult for medium to penetrate

40
Q

How can we minimize the problem of clumping?

A

Sift the powder into the vortex of stirring medium
Levitate the powder with water miscible non solvent like alcohol, glycerin or propylene glycol
Use a blender to homogenously mix the powder and solvent

41
Q

How long do most gelling agents require to completely hydrate and reach maximum viscosity and clarity?

A

24-48 hours

42
Q

Should the gel be formed first, or can you add the drug first and then the gel be formed?

A

The active drug may be added before or after the gel is formed
BUT preference is prior to forming the gel

43
Q

Characteristics of lyophobic/hydrophobic colloids:

A

No or little affinity to the dispersion medium (water)
No change in systems viscosity
Maintain dispersion due to mutual repulsion and Brownian movement
Generally inorganic molecules
Thermodynamically unstable

44
Q

What are examples of lyophobic colloids?

A

Colloidal gold (sol)
Colloidal sulfur - used as antimicrobial in anti-acne mask
Colloidal silver - toxic

PHAR 124 (4 decks)

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