Colloids

Question 1

What is the difference between colloids and suspensions?

Answer 1

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

Question 2

What are gelling agents?

Answer 2

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

Question 3

Do gelling agents increase or decrease viscosity of gelling agent?

Answer 3

Increase

Question 4

What is a two-phase system gelling agent?

Answer 4

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

Question 5

What is a one-phase system gelling agent?

Answer 5

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

Question 6

What is the usual concentration of gelling agents?

Answer 6

0.5-5%
Some up to 10%

Question 7

What are the types of gelling agents?

Answer 7

Natural polymers
Semi-synthetic polymers
Synthetic polymers

Question 8

examples of natural polymers

Answer 8

Acacia, alginic acid and tragacanth

Question 9

Examples of semi-synthetic polymers

Answer 9

Cellulose derivatives like methylcellulose

Question 10

Examples of synthetics polymers

Answer 10

Carbomers or polaxamers

Question 11

Higher gelling agent = _____

Answer 11

Stiffer (more viscous) gel

Question 12

Alginic acid is obtained from____

Answer 12

Seaweed

Question 13

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

Answer 13

1-5% and 30 minutes

Question 14

What is the strength of sodium alginate?

Answer 14

10%

Question 15

What must be added to alginic acid?

Answer 15

Preservatives because they are prone to microbial growth

Question 16

Tragacanth is used for gels that are stable at pH ____

Answer 16

4-8

Question 17

Tragacanth requires addition of ______

Answer 17

Preservatives

Question 18

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

Answer 18

Aqueous dispersions are prepared or wetting agents like glycerin are used

Question 19

At what pH do semi-synthetic agents maintain viscosity?

Answer 19

3-11
EXCEPT carboxylmethyl cellulose - 7-9

Question 20

What kind of gels does methylcullulose make?

Answer 20

Thinner gels

Question 21

What does methylcellulose have a high tolerance for?

Answer 21

Added drugs and salts

Question 22

Methylcellulose has good compatibility with _____

Answer 22

Water, alcohol and propylene glycol

Question 23

What does cooling Methylcellulose for an hour do?

Answer 23

Improves clarity and viscosity

Question 24

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

Answer 24

Thicker gels

Question 25

What is HPMC compatible with?

Answer 25

Water and alcohol

Question 26

HPMC disperses good in _____

Answer 26

Cool water

Question 27

What is HPMC a good gelling agent for?

Answer 27

Time release preparations

Question 28

What are carbomers?

Answer 28

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

Question 29

At what pH do carbomers thicken?

Answer 29

5-6, and become 1000x original volume

Question 30

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

Answer 30

Low Neutralizer Increase

Question 31

What are poloxamers?

Answer 31

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

Question 32

What is poloxamer gel base widely used for?

Answer 32

Extemporaneous compounding

Question 33

What do poloxamers form?

Answer 33

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

Question 34

What concentration are poloxamers used in?

Answer 34

15-50%

Question 35

When are gels low viscosity and high viscosity?

Answer 35

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

Question 36

What is PLO gel?

Answer 36

Poloxamer combined with lecithin and isopropyl palmitate

Question 37

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

Answer 37

Diclofenac 10%

Question 38

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

Answer 38

Aqueous phase = pluronic Organic phase = lecithin

Question 39

How does clumping occur in the preparation of gels?

Answer 39

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

Question 40

How can we minimize the problem of clumping?

Answer 40

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

Question 41

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

Answer 41

24-48 hours

Question 42

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

Answer 42

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

Question 43

Characteristics of lyophobic/hydrophobic colloids:

Answer 43

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

Question 44

What are examples of lyophobic colloids?

Answer 44

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