Greco 1

Question 1

List 4 factors that should be considered during formulation

Answer 1

1. Administration route - what dosage form is appropriate
2. Potency
3. Physio-chemical characteristics - of API (water solubility, LogP) and in relaltion to excipients
4. Stability - greater stability = longer shelf life

Question 2

Explain powders as a formulation

Answer 2

• Solid particles
• Generally heterogeneous system = particles different sizes
• Widely used in pharmaceutics as intermediates leading to other dosage forms

Question 3

List 3 characteristics of a powder

Answer 3

1. Size (volume, shape, SA)
2. Density
3. Flowability

Question 4

List the 2 methods used to obtain powders

Answer 4

1. Chemical-physical methods = clarification

2. Mechanical methods = milling (size reduction) then sieving to select powders of desired size

Question 5

What is clarification?

Answer 5

Processes aiming at removing or separating solid from a fluid (liquid or gas)
Made up of filtration and centrifugation
Either to recover the pure liquid or the solid

Question 6

List 4 mechanisms of filtration

Answer 6

1. Straining/sieving
2. Impingement
3. Attractive forces
4. Autofiltration

Question 7

Explain straining/sieving as a mechanism of filtration

Answer 7

Pores big enough to allow liquid particles through but not solid particles
However may have to pause to clear solid if large quantities

Question 8

Explain impingement as a mechanism of filtration

Answer 8

Some fluid hits the fibre with enough momentum to get retained by/stuck on the fibre
This will not happen to all particles on the same fibre - further fibres will get the rest

Question 9

Explain using attractive forces as a mechanism of filtration

Answer 9

Depends on the material being filtered and the filter material
e.g electrostatic interactions

Question 10

Explain autofiltration as a mechanism of filtration

Answer 10

Material being filtered starts filtering itself

Powder deposits on filter = cake and acts as a filter itself

Question 11

List the 4 key parameters of filtering elements

Answer 11

1. Capacity =m the mass that can filter through a given filter before it gets blocked up
2. Efficiency = how good a filter is at retaining a certain paritcle size
3. Degree of filtration = smallest particle size that a filter can retain
4. Porosity = ratio of volume of pores:total volume of filtration

Question 12

What is Darcy’s equation used to calculate?

Answer 12

The rate of filtration

Question 13

What is Darcy’s equation?

Answer 13

V/t = (K x A x ΔP) / μ x L

Question 14

What do the symbols in Darcy’s equation represent?

Answer 14

V/t = volume/time
K = constant, depends on porosity of filtering element
A = area of filter
ΔP = difference in pressure from top of filter to bottom of filter
u = viscosity of liquid being filtered
L = thickness of filtering element plus any material already filtered

Question 15

What is the end product of centrifugation?

Answer 15

Pellet of solid at the bottom, liquid at the top

Liquid usually known as supernatant

Question 16

What is the formula to calculate the ratio of centrifugal force to gravity?

Answer 16

C = F/G

C= ratio of F/G
F = centrifugal force
G = gravity

Question 17

What is the formula to calculate centrifugal force (F)?

Answer 17

F = (mv^2)/r

F = centrifugal force
m = particle mass
v = velocity
r = radius of spinning centrifuge

Question 18

What is the formula to calculate the gravity (G)?

Answer 18

G = mg

G = gravity
m = mass
g = gravitational constant

Question 19

What is the formula to calculate velocity of the centrifuge?

Answer 19

v = pi x d x n

v = velocity
d = diameter (2r)
n = rotation speed

Question 20

Based on these equations, which factors can be changed to increase the centrifugal force/effect?

Answer 20

Radius of spinning centrifuge (r) and rotation speed (n)

However better to increase speed than diameter as n is squared in the equations = great effect on C