Solutions

Question 1

What is the definition of pharmaceutical solution?

Answer 1

• Liquid preparations in which the therapeutic agent and excipients are dissolved in a liquid solvent system.

Question 2

Advantages of solution

Answer 2

• Volume of liquid dose can be measured accurately to tailor doses.
• Easy to swallow (especially paediatrics and geriatrics).
• Easy to manufacture compared to other dosage forms.
• Fast onset of action (drug already dissolved)
• Dose uniformity is assured.

Question 3

Disadvantages of solution?

Answer 3

• Less stable than solid dosage forms: major signs of instability:colour change, precipitation, microbial growth
• many drugs poorly soluble in water
• Unpleasant taste and odours are difficult to mask.

Question 4

Properties of oral solutions?

Answer 4

• Must be stable
• Palatable: flavouring, colouring and sweetening agents are often added.
• Appropriate viscosity for palatability and pourability.
• Dose in multiples of 5ml for convenience.
• At physiological pH where possible.

Question 5

What should be done to avoid drug precipitation ?

Answer 5

• Drug concentration needs to be well below saturation solubility

Question 6

Why is water the most commonly used solvent?

Answer 6

• Lack of toxicity.
• Low cost.
• purified water is used

Question 7

6 Excipients for solutions

Answer 7

• Viscosity enhancers = Improve pouring quality,
  E.g. glycerol (glycerine).
• Preservatives= Prevent microbial growth, E.g. benzoic acid
• Sweeteners= Improve palatability of oral solutions,
  E.g. sucrose, mannitol.
  -Antioxidants = Improve stability of the solutions by minimising oxidation, E.g. ascorbic acid
• Flavouring agents= mask unpleasant taste of drugs , E.g. vanilla,
• Colouring agents= Correlate with the flavouring agent, E.g. green with mint, red with strawberry flavor.

Question 8

Factors affecting chemical degradation

Answer 8

High temperature.
pH
Oxygen
UV light catalysis

Question 9

Ways to enhance solution stability

Answer 9

• Formulate at a suitable pH.
• Include excipients to enhance product stability.
• Include antioxidants or metal chelators to reduce oxidation.
• Packaged in containers that reduce light transmission.
• Purging solution with nitrogen to create nitrogen headspace.

Question 10

What can be used to increase solubility of drug?

Answer 10

-pH
- modification
- Co-solvents
- Complexation
- Surfactants

Question 11

What does drug aqueous solubility depends on ?

Answer 11

• Molecular and crystal structure
  -solvent
• pKa
• pH of the medium

Question 12

What is a co-solvent system?

Answer 12

• a water miscible or partially miscible organic solvent is mixed with water to form a modified aqueous solution

Question 13

Why do we use co-solvent systems?

Answer 13

• Many drugs are not water-soluble.
• Mostly used for non-ionic drugs where solubility cannot be adjusted by pH control.

Question 14

Cyclodextrins + 3 types

Answer 14

• made up of sugar molecules - cyclic oligosaccharides
• alpha = 6 rings, beta =7 rings, gamma = 8 rings

Question 15

Cyclodextrins complexation

Answer 15

• They are in hollow truncated cone shape.
• Hydrophilic outer wall (Highly water soluble)
• Hydrophobic inner wall = Can ‘capture’ hydrophobic molecules via non-covalent bonds

Question 16

How do surfactants increase drug solubility ?

Answer 16

• Reduces the surface tensions of liquids.
• Self-assemble to form micelles at the critical micelle concentration (CMC).
• have hydrophilic head + hydrophobic tails