9 Pharmacokinetics

Question 0

Define ‘oral bioavailability’

Answer 0

The proportion of a drug given orally that reaches the circulation unchanged.

Question 1

What occurs in the ‘pharmaceutical process’?

Answer 1

Formulation of the tablets/liquid
Work out compliance (eg. once a day)
Work out best way to administer drug

Question 2

What is the ‘therapeutic dose’?

Answer 2

The maximum tolerated dose/ minimum effective dose

Question 3

What is the ‘therapeutic window’?

Answer 3

The range of drug concentrations that will have a therapeutic effect with minimal unwanted side effects

Question 4

What is’ first-pass metabolism’ and how can it be avoided?

Answer 4

Drugs administered orally are first exposed to the liver and may be metabolised before reaching the circulation. It is avoided by using different routes of administration eg. IV, injections

Question 5

What is the ‘volume of distribution’ of a drug?

Answer 5

The theoretical volume into which a drug is distributed to if it was distributed instantaneously

Question 6

How is the ‘volume of distribution’ worked out?

Answer 6

Extrapolation of plasma levels to zero time

Question 7

What is the effect of a drug having a high level of Protein Binding Drug Interactions?

Answer 7

The drug will have a small volume of distribution and therefore a low therapeutic value.

Question 8

What is a Class I drug? What can these drugs also be called?

Answer 8

A drug administered at a dose lower than the number of albumin binding sites. They can also be called object drugs.

Question 9

What is a Class II drug? What can these drugs also be called?

Answer 9

A Class II drug is a drug given at a dose greater than the number of binding sites so displaces the class I drug. They can also be called precipitants.

Question 10

What is the relationship between drug concentration and elimination rate in First Order Kinetics?

Answer 10

Rate of elimination is proportional to concentration of drug. A constant fraction of the drug is eliminated in a unit time.

Question 11

What is the relationship between drug concentration and elimination rate in Zero Order Kinetics?

Answer 11

The rate of elimination is constant and independent of drug concentration.

Question 12

How many half lives of a drug are required to reach a steady state during repeated drug administration?

Answer 12

5

Question 13

What is a ‘loading dose’?

Answer 13

An initial large dose given at the start of a course of treatment

Question 14

Name the two ways a drug is eliminated from the system

Answer 14

Metabolic- through the liver

Excretion- through the renal system

Question 15

What happens when a drug goes through Phase I of metabolism?

Answer 15

Reduction, Oxidation, Hydrolysis to inactivate the drug

Question 16

What happens when a drug goes through Phase II of metabolism?

Answer 16

It is made soluble so it can be excreted via the kidneys

Question 17

When are drug interactions especially important?

Answer 17

When the drug has a low therapeutic ratio
When the drug is being used at the minimum effective concentration
When drug metabolism follows zero order kinetics

Question 18

Give an example of a drug interaction

Answer 18

Eg. Phenobarbitone affects Warfarin

Question 19

When can drugs be excreted via the renal system?

Answer 19

When the drugs is in the free form

Question 20

What is the pK to the drug and why is this important in renal excretion?

Answer 20

The pK of a drug is the pH at which half of the drug is ionised and half is non-ionised. The non-ionised drug can pass through membranes easily so is reabsorbed. The ionised drug leaves the body in the urine.

Question 21

What affect does acidic urine have on absorption?

Answer 21

Increases absorption

Question 22

What affect does alkaline urine have on absorption?

Answer 22

Decreases absorption