Lec 11- Emulsions, mucilaginous gels and suppositories

Question 1

Emulsion

Answer 1

Thermodynamically unstable system consisting of at least 2 immiscible liquid phases- one phase is dispersed as globules (dispersed phase) in the other liquid (continuous phase) stabilized by emulsifying agent

Question 2

Pharmaceutical uses of emulsions

Answer 2

1. For rectal, oral and topical admin of oils and oil soluble drugs
2. Formulation of oil and water soluble drugs together
3. To disguise the taste and oiliness of oils when given orally- make more palatable
4. To increase the absorption of oils and oil-soluble drugs through intestinal wall
5. Slow release intra-muscular injections
6. Total parenteral nutrition to deliver oily nutrients intravenously

Question 3

3 types of emulsions

Answer 3

1. Oil in water emulsions
2. Water in oil emulsions
3. Multiple emulsions- water droplet enclosed in an oil droplet, which is dispersed in water

Question 4

Ideal formulation

Answer 4

• globlets of dispersed phase retain their initial character and remain evenly distributed
• > aim to prevent coalescence of disperse phase (cracking) and control the rate of creaming

Question 5

What do emulsifying agents do?

Answer 5

1. Reduce interfacial tension

2. Maintain separation of droplets by forming barrier at interface

Question 6

What properties does an ideal emulsifying agent have?

Answer 6

1. Colourless, odourless, tasteless
2. Non-toxic, non-irritant
3. Able to produce stable emulsion at low concentrations

Question 7

Examples of emulsifying agents (4)

Answer 7

1. Hydrophilic colloids
2. Natural acacia
3. Methycellulose (semi synthetic(
4. Polysaccharides

Question 8

3 types of surface active agents/ surfactants

Answer 8

1. Anionic : potassium stearate
2. Cationic: cetrimide
3. Non-ionic: tweens

Question 9

What may happen if thermodynamically unstable?

Answer 9

Undergo

1. Phase inversion: irreversible, no use shaking
2. Cracking: irreversible, no use shaking
3. Creaming: reversible with gentle shaking- aggregation of glovules of disperse phase at top or bottom of emulsions

Question 10

How to improve stability?

Answer 10

1. Globule size reduction -> increase SA
2. Temperature control
3. Reduce % of disperse phase
4. Increase viscosity
5. Antioxidants may be required -> need to be soluble in the oily phase and compatible

Question 11

Preservation of emulsions

Answer 11

1. Add more. use a different one, use combinations of preservatives
2. Parabens have high oil-solubility
3. Chlorocresol
4. Check solubility of preservitive
5. Aqueous phase
6. Partitioning
7. K=Co/Cw

Question 12

Dry gum method

Answer 12

1. Clean, dry motar, flat bottom
2. Drain oil (measure carefully)
3. Disperse acacia over oil, mix gently
4. Add water all at once and stir briskly in one direction -> clicking sound, white emulsion
5. Gradually dilute primary emulsion with vehicle and dissolved ingredients
6. Transfer to pre-calibrated bottle and label

Question 13

Wet gum method

Answer 13

1. Add water to acacia gum and quickly triturate to make a mucilage
2. Add oil in small amounts to mucilage
3. Triturating thoroughly after each addition until a thick, primary emulsion is formed
4. Stabilise by mixing for several minutes then add other ingredients as for dry gum method

Question 14

Problems with compounding an emulsion

Answer 14

1. Phase inversion
2. Incorrect quantities of oil/ water used
3. Cross contamination of water/oil
4. Wet mortar used
5. Mortar too small and curved, head of pestle too rounded- insufficient shear
6. Excessive mixing at first stage with dry gum method and oil
7. Diluting primary emulsion too soon and too rapidly
8. Poor quality acacia

Question 15

Storage

Answer 15

1. Cool temperature

2. Do not freeze

Question 16

Container and labelling

Answer 16

Amber bottle, shake well before use, store in cool place