Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

SL12102 - The science of medicines Y1 > Lecture 11 - Chemical kinetics and stability of dosage forms 1 > Flashcards

Lecture 11 - Chemical kinetics and stability of dosage forms 1 Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

Why is it important that pharmaceutical products remain stable for as long as possible?

A

Chemical degradation leads to the loss of active product- loss of potency and potentially toxic degradation.

instability can also lead to reduced solubility and bioavailability.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Name five mechanisms of degradation of drugs

A

hydrolysis, oxidation, isomerization, photochemical degradation, polymerisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Hydrolysis is the most common pathway for drug breakdown. Why drugs may be degraded through hydrolysis?

A

aspirin, procaine (esters), penicillin’s (amide, lactam) and benzodiazepines (lactam)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Hydrolysis of drugs may be ……… or ……….. catalysed

A

H+
OH-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

It may be possible to modify drug structure to prevent….

A

hydrolysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Oxidation is common in drugs like…

A

steroids and sterols and polyene antibiotics (C=C), ethers and sulphur groups

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Oxidation commonly occurs via

A

peroxy radical- ROO.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Oxidation can be catalysed by…

A

Can be catalysed by action of UV, heat or trace metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe izomerization

A

Racemization- a pure enantiomer becomes a racemic mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe photochemical degradation. How can it be prevented?

A

amber glass to block UV- tablets can be coated with a UV absorbing polymer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Polymerisation of drugs occurs at ….

A

high concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

give four routes of degradation.

A
  1. Direct (A –> B where K is the rate constant). This is what we will look at
  2. Dynamic equilibrium
  3. Competitive
  4. Sequential
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the molecularity of a reaction??

A

the number of reactant molecules or ions which participate in the rate determining step

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Molecularity of reaction:
Reactions maybe unimolecular, bimolecular or even termolecular. Give rate equations of each

A

Termolecular = Rate = [A]^3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Termolecular reactions are very rare in ………. . They occur more commonly in…?

A

solution
gas phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the law of mass action?

A

When you have a number of reactants reacting together, the rate = rate constant multiplied by the concentration of reactants raised to a power equal to the number of molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does the order of reaction tell you?

A

tells you how the reactants concentration effects rate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

If you double the concentration of a reactant and the rate stays the same, the order with respect to that reactant is……..

A

0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

If you double the concentration of a reactant and the rate doubles, the order with respect to that reactant is…

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

If you double the concentration of a reactant and the rate quadruples. the order with respect to that reactant is…

A

2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

The overall order of reaction =

A

the sum of the powers of the reactants in the rate equation

22
Q

We cannot just observe an equation to find order, we need to…

A

know the individual order of each reactant and we do this through experimentally working them out

23
Q

The order is usually as small whole number but it can be….?

A

a fraction or zero

24
Q

give the basic rate equation for a first order reaction.

A
  • Rate= K[A]1
25
Q

How could you find the rate of a first order reaction using a concentration-time graph? Write an equation for this.

A

The gradient of the tangent of the concentration-time graph of the first order reaction is the rate. The change in [A] divided by the change in time = Rate.

Rate = (Δ[A])/ΔT = K[A]

26
Q

What is the integrated first order rate equation?

A
27
Q

The units of the rate constant depend upon the

A

order of reaction
use the units given

28
Q

K is always…

A

positive

29
Q

Integrated equation for rate constant for a first order reaction

A
30
Q

First order half life:

At half life, how much of the drug remains?

A

HALF the concentration of the drug

31
Q

Half life for first order reaction equation

A
32
Q

Define shelf life.

A

Shelf life of a medicine is the time that a specific drug characteristic remains within a particular specification after manufacture when stored according to the label.

33
Q

Shelf life can be based upon one of two things..

A
  • Can be based on the amount of drug remaining or the accumulation of degradation product.
34
Q

shelf life may be estimated mathematically through

A

extrapolation

35
Q

In our lectures, shelf-life was defined as…

A

95% of the label dose.

36
Q

Give equation for shelf life of first order reaction.

A
37
Q

In a first order reaction, shelf life is intendent of…

A

initial concentration of the drug.

38
Q

We can find the ratio between half life and shelf life. Give the equation for first order.

A
39
Q

Give the step by step method to find k, half life and shelf life using time and concentrations of a drug.

A

Calculate ln values from the data

Plot ln of residual % drug versus time on linear graph paper

Calculate rate constant k from slope (m = -k)

Calculate half-life (t½ = 0.693 / k)

Calculate shelf-life (t95% = 0.0513 / k)

40
Q

Describe untrue/pseudo zero order. Use suspensions to explain.

A
  • In a 1st order reaction, the rate decreases throughout the reaction because the concentration of A decreases.
  • But, if drug A could be replenished, the rate would be a constant. For example, suspensions.
  • In suspensions, there are solid undissolved particles and also a percentage of the drug in solution. The drug will only degrade in solution.
  • A in solution is replenished by dissolution of solid drug particles- this keeps the concentration of A constant.
41
Q

pseudo/untrue zero order:
The constant concentration = constant rate. Therefore, what would the concentration-time graph look like?

A

straight line with negative gradient.

42
Q

What is the integrated zero order equation?

A
43
Q

Graphical zero order K equation

A
44
Q

Zero order half life equation

A
45
Q

zero order shelf life equation

A
46
Q

In zero order, the shelf life is indepedent of…..

A

initial concentration

47
Q

Give the equation for ratio of half life to shelf life in zero order reactions

A
48
Q

in pseudo zero order reactions, once the solid particles in suspension are fully solubilized in solution…?

A

Once the solid particles in suspensions are fully solubilized in solution, the degradation will no longer follow zero order. You then get first order degradation.

49
Q

In first order reactions, a plot of ln[A] against time gives a straight line with a slope of = -k. How does this differ to zero order?

A

in zero order, a plot of [A] against time fives a straight line with a slope of = -k

50
Q

In first order, K is described in terms of seconds-1. How does this differ to zero order

A

SI units of zero order = moles, litre, seconds

51
Q

For first order, shelf life is independent of initial concentration. How does this differ to zero order?

A

Shelf life is dependent on initial concentration.

SL12102 - The science of medicines Y1 (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions