Pharmacokinetics 2

Question 1

What are 3 things pharmacokinetic models allow?

Answer 1

1. Summarization
2. Comparison
3. Prediction

Question 2

Name 2 pharmacokinetic models

Answer 2

1. One-compartment

2. Two-compartment

Question 3

What is the key point of 1st order kinetic drugs?

Answer 3

Half-life of the drug is constant

Question 4

What 2 assumptions are made in a one-compartment model?

Answer 4

Once an injection or absorption has occurred:

1. Drug is distributed instantaneously throughout all tissues into which it will distribute
2. [Drug} in distributed tissues are not identical but rates of changes are same during elimination

Question 5

Draw the graph of one-compartment mode [plasma] v time and mark the point of equilibrium

Answer 5

See Pharmacokinetics 2 Lecture - Slide 9

Question 6

Why is the oral drug concentration line always lower than i.e. line?

Answer 6

First pass effect

Question 7

What is the difference between one and two compartment models with respect to distribution?

Answer 7

Two-compartment model accounts for non-instant distribution

Question 8

Draw the graph of two-compartment mode [plasma] v time and mark the point of equilibrium

Answer 8

See Pharmacokinetics 2 Lecture - Slide 10

Question 9

Give the main characteristic of the graph of two-compartment mode [plasma] v time

Answer 9

• Rapid decline seen after absorption or I.V. injection as distribution rate quicker than elimination
• Once equilibrium reached rate of decline of drug reduces as rate of elimination is identical in all tissues

Question 10

What is the abbreviation for half-life?

Answer 10

T½

Question 11

What is the relationship between half life and clearance?

Answer 11

Inversely proportional

Question 12

When is a drug essentially eliminated?

Answer 12

After 5 t½s have passed

Question 13

Name 3 things which affect half life

Answer 13

1. Physiological or pathological states
2. Altered by smoking
3. Subject to genetic variation

Question 14

Name 4 physiological or pathological states that can alter half life

Answer 14

1. Age
2. Cardiovascular disease
3. Renal disease
4. Hepatic disease

Question 15

How does smoking generally affect the half-life of a drug?

Answer 15

Usually decreases the half life of a drug

Question 16

With regards to elimination rate, what is the difference between first order and zero order kinetics?

Answer 16

In first order kinetics, elimination rate always changes but it is constant in zero order kinetics

Question 17

Why can zero order processes occur?

Answer 17

Elimination processes become saturated in therapeutic concentration range

Question 18

What is the major example of a drug whose elimination pathways become saturated at low concentrations?

Answer 18

Ethanol (Alcohol)

Question 19

What 2 factors influence the amount of drug infused in an I.V. infusion?

Answer 19

1. Flow rate

2. [Drug in Solution]

Question 20

What is a steady state level?

Answer 20

When the rate of elimination is equal to the rate of infusion

Question 21

How is bioavailability calculated from a [plasma] v time graph?

Answer 21

• Calculate area under I.V. graph
• Calculate area under oral graph
• BA = Oral area / I.V. area

Question 22

What does the area under a line in a [plasma] v time graph represent?

Answer 22

Volume of drug which is absorbed

Question 23

What is the main aim of dosage determination?

Answer 23

Achieve a concentration of drug at its site of action in order to produce an effective therapeutic effect

Question 24

What is a loading dose of a drug?

Answer 24

A rapid achievement of target concentration is required (usually administered by I.V. infusion)

Question 25

How is the target concentration of a drug calculated?

Answer 25

Vd = Dose / TC

Question 26

What is a maintenance dose of a drug?

Answer 26

The dose calculated to achieve a steady state level replacing the drug eliminated

Question 27

What information is necessary to work out the loading dose in a human?

Answer 27

Weight of the person receiving the dose

Question 28

How is a loading dose calculated?

Answer 28

Dose = Vd x TC

Question 29

How is Vd calculated if a patient’s weight is known?

Answer 29

Vd = Weight x Drug distribution

Question 30

How is the dosing rate calculated?

Answer 30

Dosing Rate = Clearance x TC

Question 31

How is the maintenance dose calculated?

Answer 31

Maintenance dose = (Dosing Rate x Dosing interval) / Bioavailability

Question 32

What must be taken into account if switching from I.V. and oral administration of a drug?

Answer 32

Bioavailability will be different so dosage must be changed

Question 33

Why may vomiting affect the effects of a drug

Answer 33

Vomiting can lead to dehydration