Buffered isotonic solutions

Question 1

Define buffers

Answer 1

Acid (or base) and its salt.

Used to minimise the change of pH upon the addition of a small amount of acid or base to the solution

Question 2

Define osmosis

Answer 2

the spontaneous diffusion of water from the low solute concentration reservoir into a more concentrated solution at constant temperature and pressure
Leads to a decrease in solute concentration

Question 3

Define colligative properites

Answer 3

properties of solutions that depend upon the number of solvent molecules in a solution and NOT on the type of chemical species present. The number ratio can be related to the various units for concentration of solution

Question 4

Explain the role of buffers, osmosis and colligative properties in pharmaceutical formulations

Answer 4

Increase in drugs solubility will increase its stability over time and decrease any physiological difference with the site of delivery which may result in undesired secondary effects

Question 5

What is the buffer range

Answer 5

The range of pH values for which the efficiency of a buffer is the highest
0.1

Question 6

Write the Hendersson-Hasselbach equations

Answer 6

pH=pKa+log(salt/acid)

pH=pKa+log(base/salt)

Question 7

Explain the role of buffers in oral solutions

Answer 7

usually controlled by the salt form or by-
-Hydrochloric acid
-tartaric acid
benzoic acid
citric acid

Question 8

Explain the role of buffers in injectable solutions

Answer 8

Drug solubilised at desired concentration by pH adjustment (provided pKa is far enough from the formulation pH)

Question 9

What is the acceptable pH range for IV and IM injection solutions?

Answer 9

2-12

Question 10

What is the acceptable pH range for subcutaneous injection solutions?

Answer 10

2.7-9 because dilution rate is reduced and to reduce irritation at the injection site

Question 11

How is the pH of injectable solutions controlled?

Answer 11

either

• a salt form of the drug
• strong acids/bases such as HCl and NaOH
• or a buffer

Question 12

Name 8 buffers used for injectable solutions

Answer 12

Glycine
Citrate
Acetate
Histidine
Phosphate
Borate
TRIS
Carbonate

Question 13

Why does a buffer maintain the solubility of the therapeutic agent in a drug solution?

Answer 13

Because solubility is pH dependent

Question 14

Chemical stability is dependant on what 2 factors?

Answer 14

pH and hence buffer dependent

Question 15

The pH of a buffer extends +/- 1 pH unit around the..

Answer 15

pKa

Question 16

What is an isotonic solution?

Answer 16

Solution with the same osmolarity either part of a membrane

Question 17

How are solutions made isotonic?

Answer 17

Via addition of an adjusting substance e.g. NaCl

Question 18

Define osmotic pressure

Answer 18

Pressure applied to oppose swelling of a membrane caused by water movement
osmotic pressure is a colligative property

Question 19

What does isotonic correct depend upon? (2 factors)

Answer 19

Type of membrane

Type of drug

Question 20

An osmotically active particle may be…

Answer 20

an ion or a molecule. Basically a particle dissolved regardless of its charge, weight or size

Question 21

When does osmolarity=molarity?

Answer 21

for uncharged particles

Question 22

For NaCl 1M, what is the osmolarity and why?

Answer 22

2 osmolar as two ions present

Question 23

Osmolarity is a property of…

independent of…

Answer 23

a solution

type of membrane

Question 24

Human plasma osmolarity =

Answer 24

320mOsmol

Question 25

Define tonicity

Answer 25

measure of osmotic pressure exerted on a membrane

thus specific to the type of membrane

Question 26

Two solutions on either side of a membrane with the same tonicity are…

Answer 26

isotonic

Question 27

As it relates to the osmotic pressure… what kind of molecules are the only ones considered in a calculation for tonicity

Answer 27

non-permeant molecules

Question 28

3 Methods to alter tonicity?

Answer 28

freezing point depression
sodium chloride equivalent method (E value)
white-vincent method/USP method

Question 29

What is freezing point depression?

Answer 29

The difference between the freezing point (fp) of water and the fp of the solution

Question 30

What is the freezing point of blood?

Answer 30

0.52 degrees celcius

Question 31

If you adjust the tonicity of a solution for the body to that of blood you get

Answer 31

an isotonic solution

Question 32

What adjusting substance can be added when adjusting the tonicity of a drug solution?

Answer 32

NaCl

Question 33

Equation for freezing point (fp) depression of an isotonic solution

Answer 33

fp(drug) + fp(adjusting substance) = fp(blood)

if equation is correct then solution is isotonic