Lecture 19- Kinetics Of Degredation 2

Question 1

Order of reaction

Answer 1

Zero, first, second order reaction

Question 2

Zero order reactions

Answer 2

Loss of drug is independent of the concentration of the reactants and the rate is constant
Dc/dt= k
K= zero order rate constant
Reaction rates are commonly described by k or half-life t1/2

Half life equation; t1/2= (1/2)(Co/k)
If C0 (initial conc of the drug) changes, the half life also changes. Inverse relationship between k and t 1/2

Slide 6
Go over calcs

Question 3

First order reaction

Answer 3

Loss of drug is directly proportional to the concentration remaining with respect to time. Called a first order reaction and has the units of reciprocal time, time-1

Expression -d[C]/dt=k[C]
C= conc of intact drug remaining
T= time
Dc/dt= rate at which the intact drug degrades and k is the specific reaction rate constant

Question 4

Second order reaction

Answer 4

Rate depends on the product of two conc terms
Two components reacting with each other or one component reacting with itself

Question 5

Arrhenius equation

Answer 5

Most reaction rates depend on;
Fraction of molecules possessing energy of activation
Number of collisions per second
Fraction of molecules having the correct orientation

Inc in reaction rate is NOT linear with increase in temp in most reactions

Question 6

Approaches to increase the stability of pharmaceutical preps contains drugs subject to hydrolysis

Answer 6

-Applying a waterproof protective coating over tablets or by keeping the drug in a tightly closed container
-Drug may be supplied in a dry form for reconstitution by adding a specified amount of purified water before dispensing
-Refrigeration for most preps subject to hydrolysis
-pH = major determinant of the stability of a drug prone to hydrolytic decomposition
-buffering agents

Question 7

Approaches to increase the stability of pharmaceutical preps contains drugs subject to photodegredation

Answer 7

May occur during storage and during the use of the product (in some topical drugs)
Can be protected when stored in amber coloured bottles and a dark place
Are protected by coating with polymer containing UV light absorbing substance