Pharmacokinetics

Question 1

Why is Insulin only administered parenterally?

Answer 1

Because insulin is a peptide hormone

Meaning that proteolytic enzymes can rapidly degrade it

Parenteral routes avoid the GI tract and hence proteolytic enzymes

Question 2

Why might a weakly acidic drug like Aspirin start to be absorbed in the stomach?

Answer 2

The pH of the stomach influences the drug becoming unionised therefore being ready to be absorbed

Question 3

Why are oral doses in higher volume compared to parenteral doses?

Answer 3

Oral doses go through significant first-pass metabolism when administered

The parental dosage is usually lower as it is already in the system and can exert it effect

Question 4

What is the hepatic-first pass effect?

Answer 4

The variable amount of. an orally administered frug that is metabolised by the liver before entering the blood

Question 5

How do you calculate the oral bioavailability?

Answer 5

Multiply the fraction of the drug absorbed

by the fraction of the absorbed drug escaping hepatic extraction

Question 6

Why might a drug have a lower bioavailability

Answer 6

- The drug was not very wellabsorbed. This may be due to :
o	Not soluble in lipids 
o	Ionised 
o	Not dissolved
o	Lasrge molecule 

• It may also have been degraded by the acidity of the stomach or ptoeolytic enzymes
• It also undergoes intermediate hepatic clearance

Question 7

The higher the drug is bound to plasma proteins the ________ the drug effect

Answer 7

Lower

Only unbound drugs are able to exert pharmacological effects

Question 8

Are all drugs metabolised by the liver?

Answer 8

• False

The majority of drugs undergo metabolism to some extent in the liver. Some drugs are excreted as unchanged parent drugs

Question 9

Do all products of metabolism have less biological activity than the parent drug?

Answer 9

For normal drugs, yes

However not for prodrugs as they are inactive until converted to the active drug in the liver

Question 10

Differentiate between functionalisation reactions and conjugation reactions

Answer 10

Functionalization reactions

• Enzymatic process introduces a function group to the drug molecule
• Reactions include oxidation, reduction and hydrolysis
• These reactions produce a more water-soluble metabolite; hence favoring excretion

Conjugation reactions

• Conjugation reactions involve joining the drug molecule with a. polar substance
• Conjugated molecules are more water soluble; hence favoring excretion

Question 11

What is enterohepatic cycling?

Answer 11

• Drug is absorbed from the small intestine
• It then enters the liver via the portal vein where it may be metabolised or not
• The drug or drug metabolites is then excreted into bile
• Bile is then released into the small intestine where the drug is once again reabsorbed and returned to the liver via the portal vein, hence the term ‘cycling’
• Main drugs are excreted in bile to some extent (e.g. Atorvastatin, digoxin), they are likely to undergo enterohepatic, cycling to some d
• Sometimes a drug metabolite