Shelf Life and Overage & Stability Testing

Question 1

What is shelf life?

Answer 1

time required for initial conc to fall by 10% (5% for potent drugs)

Question 2

How do you work out shelf life for zero order kinetics?

Answer 2

t₉₀ = C₀/10k

Question 3

How do you work out shelf life for first order?

Answer 3

t₉₀ = ln(100/90)/k

Question 4

How do you work out shelf life for second order?

Answer 4

t₉₀ = 1/9C₀k

Question 5

What is overage?

Answer 5

excess of API that can be added to a dosage form to prevent a loss of drug potency due to degradation

Question 6

How do you calculate overage for zero order?

Answer 6

overage = C_x

C = (C₀ + C_x) - kt

C_x = C - C₀ + kt

Question 7

How do you calculate overage for first order?

Answer 7

lnC = lnC₀ - kt

=

C = C₀e^-kt

so its C = (C₀ + C_x) e^-kt

C_x = C/e^-kt - C₀

Question 8

What is the Arrhenius equation and what does it tell you?

Answer 8

k = A_ce^-Ea/RT

A_c = Arrhenius constant

Ea = activation factor

R = universal gas constant 8.314 J/mol.K

Question 9

What is the activation rate in terms of Arrhenius?

Answer 9

diff between average energy of reactants and minimum energy required for them to react

Question 10

Display Arrhenius as y = mx + c

Answer 10

lnk = (-Ea/R x 1/T) + lnAc

Question 11

Why is Arrhenius equation useful?

Answer 11

used to predict stability under storage conditions

• reduction in testing time
• early rejection of unsatisfactory formulationd