Fundamentals of drugs

Question 1

What is a solution?

Answer 1

A homogenous mixture of 2 or more substances

Question 2

What is the solute(s)?

Answer 2

The substance present in the smaller amounts

Question 3

What is the solvent?

Answer 3

The substance present in the larger amount

Question 4

What is solubility?

Answer 4

The number of parts of solvent (by volume) that will dissolve ONE PART of solute (by weight) [Can also be defined as the amount of solute that passes into solution]

Question 5

Describe an unsaturated solution

Answer 5

-More solute dissolves
-No solid remains in flask
-SOLUBILITY not reached yet

Question 6

Describe a saturated solution

Answer 6

-No more solute can dissolve
-Undissolved solid remains in flask
-Maximum limit of SOLUBILITY is reached

Question 7

Describe a supersaturated solution

Answer 7

-More solute than is normally possible
-Becomes unstable, crystals forming
-Maximum limit of solubility is exceeded

Question 8

What can be done to improve the solubility of poorly soluble drugs?

Answer 8

Adding water miscible solvents in which the compound is soluble (i.e a cosolvent)

Question 9

(Solubility enhancement) An ideal cosolvent should…(2)

Answer 9

1. Enhance the solubility of the drug
2. Be safe (non toxic)

Question 10

What is the most commonly used cosolvent (+ two others)

Answer 10

1. Ethanol
   -glycerol, glycol

Question 11

(Solubility enhancement) Why might you want to adjust the pH of a drug? (3 points)

Answer 11

-Most drugs are weak acids or weak bases (proportion of ionised to unionised fraction depends on the pH of the medium)
-We want drugs in their more ionised form as they are more water-soluble
-For weak acids to increase ionised fraction you will increase the pH but for weak bases you must lower the pH

Question 12

Three things to be wary of when manipulating the pH of solution.

Answer 12

1) Membrane irritation at extreme pH values
2) Formulation compatibilities
3) Formulation-container compatibility

Question 13

(Solubility enhancement)What is solubilisation?

Answer 13

The addition of surfactants (surface active agents) may be used as a strategy to solubilise poorly soluble drugs

Question 14

5 things a surfactant should be

Answer 14

1- Non-toxic
2- Miscible with the solvent system
3)Compatible with the other ingredients and the container
4) Free from bad odour
5) In case of oral administration- free from bad taste

Question 15

(solubility enhancement) What is chemical modification? + example

Answer 15

When a drug is chemically modified to produce a water soluble derivative (usually salt form)
- Sodium phosphate salt of hydrocortisone