Pharm 3

Question 1

What structural changes are involved in the metabolism of a drug?

Answer 1

Biotransformation of a lipophilic compound to a more hydrophilic compound to facilitate elimination.

Question 2

What are the two phases involved in drug metabolism?

Answer 2

1. Phase 1 (the P450 enzymes)

2. Phase 2 (glucuronidation) - particularly slow in felines where larger doses are required

Question 3

Provide an example of a drug that will induce hepatic enzymes:

Answer 3

anti-convolscent drugs

Question 4

Provide an example of a drug that will inhibit hepatic enzymes:

Answer 4

ketoconazole (an anti fungal) inhibits the metabolism of a more expensive drug (cyclosporine)

Question 5

What is meant by the term “sequelae to metabolism” and what is an example of a drug that has this action?

Answer 5

This is where the conversion of prodrugs occurs through the formation of an active metabolite (e.g. tramadol, prednisone)

Question 6

What is the main site of elimination for drugs?

Answer 6

kidneys

Question 7

What is the pharmokinetic parameter clearance (PI)?

Answer 7

Elimination is quantified by clearance which represents the addition of all of the clearance pathways summed together to get a number

Question 8

Define the terms full antagonist, full agonist, partial response and mixed agonist-anatagonist?

Answer 8

• No response at all = full antagonist
• Full response = full agonist
• Partial response = partial agonist
• Mixed agonist-antagonist = agonist at one particular receptor while being an antagonist at another (e.g. butorphanol)

Question 9

Compare the terms drug potency and drug efficacy:

Answer 9

• Potency of drug = [drug] required for half of its effect. No influence on the magnitude of the effect
• Magnitude of a drug’s effect = efficacy

Question 10

Differentiate between the terms loading dose and maintenance dose:

Answer 10

• The Loading Dose = the amount of drug that is given initially to obtain the desired [plasma] as soon as possible (mg/kg).
• The Maintenance Dose = rate at which the drug needs to be administered to maintain the desired plasma concentration (mg/kg/min) important to realise it has a time element in it.

Question 11

If the loading dose is not administered will the required plasma concentration still be achieved?

Answer 11

If the initial loading dose is not administered the plasma dose will still be achieved it will just take a lot longer

Question 12

What are the factors that can limit how loading doses are administered?

Answer 12

1. Volume of distribution

2. Toxicity of the drug

Question 13

What are the factors to consider when converting the maintenance dose into a practical dosing interval?

Answer 13

• How quickly the plasma drug concentration decreases (the drug’s half-life)
• The therapeutic window and compliance
• Compliance – maximum compliance by giving higher doses less often (problem lies with jumping up plasma concentrations to very high levels) . This method is largely limited by the span of the therapeutic window