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Pharmaceutics Year 2 > Section 1 - Drug Stability > Flashcards

Section 1 - Drug Stability Flashcards

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1
Q

What is drug stability?

A

The extent to which a product retains the same properties and characteristics it possessed at the time of manufacture

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2
Q

What does drug stability refer to?

A

Shelf life

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3
Q

What are the 3 areas of concern with drug stability?

A

1) Chemical - active ingredients retain chemical integrity and potency
2) Physical - dissolution and appearance are retained
3) Microbiological - sterility or resistance to microbial growth are retained

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4
Q

What can chemical degradation of active ingredients lead to?

A
  • Inaccuracy in dosing

- Possible therapeutic failure

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5
Q

What is the allowed amount of degradation?

A

2-10%, but tighter control if the degradants are toxic

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6
Q

What can physical degradation lead to?

A
  • Reduced bioavailability

- Reduced efficacy

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7
Q

What can cause physical degradation?

A

Physicochemical changes to active or excipient ingredients

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8
Q

What are some examples of physicochemical changes that can cause physical degradation?

A
  • Production of polymorphs
  • Loss of volatiles
  • Dissolution changes from aging
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9
Q

What are some examples of physicochemical changes that don’t affect efficacy, but affect elegance?

A
  • Mottling of tablets
  • Caking of suspensions
  • Colour changes of solutions
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10
Q

How can products resist microbial growth?

A

Preservatives, which must retain efficacy over the entire shelf-life

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11
Q

What is hydrolysis?

A

Decomposition of a drug through a reaction with water

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12
Q

In a hydrolysis reaction, water acts as a _____ and attacks _____

A
  • Nucleophilic agent

- Attacks electrophilic sites of a drug molecule

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13
Q

What are the most common functional groups involved in hydrolysis reactions?

A

Carboxyl derivatives

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14
Q

Why are penicillins susceptible to hydrolysis?

A

Because of the steric strain on their 4 membered beta-lactam ring

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15
Q

Oxidation reactions are often mediated through _____

A

Atmospheric oxygen

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16
Q

What is different about the products of oxidative processes?

A

They are usually electronically more conjugated, so their colour and scent change

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17
Q

In what types of solutions can oxidation reactions occur?

A
  • Aqueous
  • Non-aqueous
  • Solid state
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18
Q

Can oxidation reactions cause products to become unfit?

A

Yes

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19
Q

What are the 3 types of oxidation reactions?

A
  • Loss of electrons
  • Loss of hydrogen
  • Gain of oxygen
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20
Q

Since oxidation is the loss of electrons, what generally goes along with the loss of electrons?

A

Change in structure and transfer of protons

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21
Q

What is an autoxidative reaction?

A

An oxidation reaction that requires a free-radical and occurs spontaneously

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22
Q

What are the 3 steps of an autoxidative reaction and what occurs in each step?

A

1) Initiation - generation of a free radical
2) Propagation - further release of free radicals
3) Termination - free radicals come together to form a non-radical

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23
Q

What is photolysis?

A

When light provides the energy for initiation of an oxidative process (although not always oxidative)

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24
Q

What may happen when electromagnetic radiation is absorbed by a molecule?

A

1) Molecule decomposes with release of free radical
2) Energy is retained, causing a chemical change
3) Energy is converted to heat and no reaction occurs
4) Absorbing molecules emit light of a different wavelength

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25
What are 2 examples of dehydration reactions?
1) Tetracycline -> epidehydrotetracycline | 2) Prostaglandin E2 -> prostaglandin A2
26
Is dehydration a chemical change?
No, it changes the crystal habit of the drug which may result in solubility changes
27
What can dehydration produce?
Pseudopolymorphs
28
What are the 5 types of chemical degradation reactions?
1) Hydrolysis 2) Oxidation 3) Photolysis 4) Dehydration 5) Racemization
29
Polymorphs differ in ______
Crystal structure and crystal energies
30
Can polymorphs cause a product to be unusable?
Yes, sometimes
31
What is needed for a drug to be lost through vaporization?
The drug needs a high vapor pressure
32
What is an example of physical degradation that occurs in tablets?
Hardening or softening, which alters disintegration and bioavailability
33
What are 4 types of physical degradations?
1) Polymorphism 2) Vaporization 3) Aging 4) Adsorption
34
What occurs in adsorption?
Drug is lost to packaging materials
35
Which drug delivery method is most prone to adsorption?
IV
36
How can adsorption be avoided?
Careful selection of the container
37
What is t90?
- Shelf life | - The time it takes the initial concentration of the active ingredient to be decreased by 10%
38
What does the order of the reaction determine?
The shape of the concentration-time profile
39
What determines the slope of the concentration-time profile?
The rate constant
40
Which orders of reactions are most common in drug stability?
Zero, first, and second
41
What is a zero order reaction?
A constant amount of drug is eliminated per unit time; independent of concentration
42
What is a first order reaction?
The rate of decrease of substrate molecules is proportional to the concentration of substrate molecules remaining
43
What is a second order reaction?
The overall order of the reaction is the sum of the exponents of the concentration terms
44
Is it important to make a distinction between the orders of reactions?
No
45
Which order of kinetics are expiration dates usually based on?
Zero or first
46
What is the unit for a first order rate constant?
t^-1
47
What will the slope be of a plot of log[D] vs. time?
-k1 / 2.303
48
What is constant in a first order reaction?
Half life
49
What is the shelf life of a zero order reaction equal to?
0.1 [D]o / Ko
50
What is plotted on the graph for a zero order reaction?
[D] vs. time
51
What is plotted on the graph for a second order reaction?
1/[D] vs. time
52
What are 5 factors affecting reaction rate?
1) Temperature 2) Catalysis 3) pH effects 4) Solvent 5) Solubility
53
What are reaction rates proportional to?
The number of collisions between particles
54
What will the slope be of a plot of log k against the inverse of absolute temperature?
Slope = -Ea/2.303R
55
What is the typical range for Ea for drug decomposition reactions?
12-24 Kcal/mol
56
What are 2 common catalysts of oxidation reactions?
Iron and copper
57
How can you prevent iron and copper from catalyzing oxidation reactions?
Add something that kelates with them
58
Reaction rates in aqueous solutions are often dependent on _____
The pH of the solution
59
What can you learn from studying the pH effects on reaction rates?
- The mechanism | - The stability of the drug
60
What is plotted on a pH-rate profile?
Rate constant (log k for first order or k for zero order) against pH
61
When would a V-shaped pH-rate profile be expected?
When the substrate is non-ionizable and is subject to hydrolysis
62
When would a sigmoid shaped pH-rate profile be expected?
When the drug molecule undergoes an acid/base dissociation (an ionizable substrate)
63
Do chemically-related compounds generally have similar pH-rate profiles?
Yes
64
What are the most common solvents used to solubilize a drug?
- Alcohol - Propylene glycol - Glycerol - Polymeric alcohols
65
Do solvents have a small or large impact on stability?
Large
66
What impact does solvent polarity have on reaction rate?
- As solvent polarity increases, the rate will increase when there is a charge is developed in the activated complex - Rate will decrease when there is less charge in the activated complex than the starting materials - Rate will be unaffected when there is little or no difference in charge between reactants and activated complex
67
How can solvents change pKa?
By shifting the dissociation equilibrium
68
How can a drug be stabilized using solubility?
It can be made into an insoluble salt and formulated into a suspension
69
What does reduced solubility in a suspension mean?
It decreases the amount of drug available for reaction
70
What is the typical order of reaction for a drug in a solution?
First
71
What is the typical order of reaction for a drug in suspension?
Zero
72
What are 2 stabilization strategies?
1) Hydrolysis | 2) Oxidation
73
What is needed for hydrolysis to occur and why?
- Drug must be in solution | - Exclusion of water will slow the rate
74
How can hydrolysis be achieved?
By formulating the product as a solid dose form (tablet, capsule)
75
Is total exclusion of water possible?
Not usually
76
What can allow for control over hydrolysis rate?
Control of pH
77
Can every drug be frozen?
No, only the ones that show no deleterious effect
78
What can freezing do to a drug?
- For some, it can increase product stability | - For others, it can increase the rate of degradation (ex: ampicillin)
79
How can drugs be protected from light?
- Tinted glass | - Opaque plastics
80
How can oxygen be removed and what is this used for?
- Oxygen is purged with inert gas (usually nitrogen) and sealed - Used for parenterals

Pharmaceutics Year 2 (17 decks)

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