Drug Analysis

Question 1

What is the purpose of the aspirin experiment?

Answer 1

Measuring the elimination of aspirin metabolites in urine following administration of different formulations of the drug

Question 2

What are the safety precautions for the aspirin experiment? (5)

Answer 2

• Do not take if intolerant/medical condition causing NSAID contraindication
• No alcohol night before
• No caffeine in 2 hours before-during session
• Gloves/specs/lab coat
• No mercury down sink

Question 3

What other compound was administered prior to aspirin for everyone except 1 member?

Answer 3

Sodium bicarbonate

Question 4

What type of assay was used to measure the salicylate content of urine?

Answer 4

Simple colurimetric assay

Question 5

What is measured in the urine and how does this indicate the rate of formulation absorption?

Answer 5

• Salicylate content (aspirin metabolite)

- Rate at which metabolites appear in urine: rate at which absorbed into blood

Question 6

What is the rate at which salicylate appears in urine influenced by? (2)

Answer 6

• Urinary pH

- Different aspirin formulations

Question 7

What 3 formulations of aspirin were compared in the practical?

Answer 7

• Aspirin standard tablets B.P
• Soluble aspirin
• Enteric coated aspirin

Question 8

Describe the solubility of the aspirin standard tablets B.P

Answer 8

Poor

Question 9

What does the soluble aspirin being soluble affect?

Answer 9

Absorption into blood = rapid

Question 10

How is soluble aspirin taken? (2)

Answer 10

• Dissolved in water

- Solution swallowed

Question 11

What do enteric coated aspirin tablets have?

Answer 11

A sugar wax coating = must dissolved before aspirin absorbed into blood

Question 12

Why are aspirin tablets enteric coated?

Answer 12

• Slows down aspirin absorption

- Reduces likelihood of gastric side effects e.g ulceration

Question 13

Who are enteric coated aspirin tablets particularly important for? Give an example

Answer 13

Patients taking aspirin daily e.g rheumatoid arthritis=10g daily

Question 14

What is drug formulation?

Answer 14

Make up of tablet/oral dose

Question 15

Does drug formulation directly effect pharmacodynamics?

Answer 15

No, but indirectly through effecting pharmacokinetics

Question 16

How is drug formulation important in oral drug administration? (2)

Answer 16

• Affects rate of absorption

- So affects rate at which drug metabolites appear in urine

Question 17

What effect does prior administration of sodium bicarbonate have on aspirin as a weak acid drug and why? (2)

Answer 17

• Increases fraction of drug/metabolite (aspirin/salicylate) in ionised form
• As increases pH of urine

Question 18

According to what equation does sodium bicarbonate increase the ionised form of aspirin as a weak acid?

Answer 18

pH = pKa + log10([ionised drug]/[unionised drug])

Question 19

According to what equation does sodium bicarbonate decreases the fraction of a weak base drug in ionised form?

Answer 19

pH = pKa + log10([unionised drug]/[ionised drug])

Question 20

Give an example of a weak base drug

Answer 20

Amphetamine

Question 21

What effect does prior administration of sodium bicarbonate have on a weak base drug and why?

Answer 21

• Decreases fraction of drug/metabolite in ionised form

- As increases pH of urine

Question 22

In a curve of salcylate content (i.e excretion in urine) over time, what drug formulation causes the highest salicylate content and what does this show?

Answer 22

Soluble aspirin - leads to highest urine excretion

Question 23

In a curve of salcylate content (i.e excretion in urine) over time, what 2 drug formulations have the same area under the curve even though the 1st causes a higher salicylate content?

Answer 23

• Soluble aspirin

- Aspirin tablets BP

Question 24

In a curve of salcylate content (i.e excretion in urine) over time, what drug formulations has the highest area under the curve?

Answer 24

Enteric coated aspirin

Question 25

In a curve of salcylate content (i.e excretion in urine) over time, would the area under the curve change after prior sodium bicarbonate administration?

Answer 25

No

Question 26

How does prior bicarbonate administration to aspirin ingestion affect rate of excretion and why? (6)

Answer 26

- A weak acid drug will be unionised in an acidic solutions (no anions to cause ionisation) - In a basic solution, more weak acid drug will be ionised - So can't be reabsorbed because its in its ionised form - not lipid soluble - Therefore excreted - Ingest bicarb, makes more urine more basic, more ionisation - Increased rate of excretion

Question 27

In a curve of salcylate content (i.e excretion in urine) over time, why does enteric coated aspirin have the highest area under the curve? (2)

Answer 27

- Takes the longest time to release aspirin | - Content spread over more time

Question 28

In a curve of salcylate content (i.e excretion in urine) over time, why do aspirin tablets BP and soluble aspirin have the same area under the curve even though the soluble aspirin causes a higher salicylate content?

Answer 28

Times the same amount of time to release aspirin, just soluble aspirin causes more to be absorbed in blood so more salicylate content