1.2 Pharmacokinetics

Question 1

Pharmacokinetics

Answer 1

The handling of the drug by the body

Question 2

ADME

Answer 2

Absorption
Distribution
Metabolism
Excretion

Question 3

List possible routes of drug administration

Answer 3

Oral
Rectal
Percutaneous
Intravenous
Intramuscular
Intrathecal
Inhalation

Question 4

Plasma Protein Binding

Answer 4

Drugs that bind to proteins within plasma. Albumin most common. Only free fraction of the drug is active and can be eliminated

Question 5

Clearance

Answer 5

Irreversible elimination of the drug

Question 6

Two possible forms of Clearance

Answer 6

Excretion of unchanged drug. (e.g. by the kidneys in the urine)
Metabolisms into a different chemical (liver)

Question 7

How is Clearance quantified?

Answer 7

Volume of blood cleared of drug per unit time (e.g. L/h).

Question 8

What effects how much a drug can be eliminated by a given organ

Answer 8

The blood flow though that organ.

Question 9

What does clearance determine?

Answer 9

Maintenance dose. The dose required to maintain target plasma concentration at steady state

Question 10

Volume of Distribution

Answer 10

Hypothetical volume of body fluid necessary if total amount of drug were distributed at same concentration as plasma; Can give approximation of distribution of compound throughout the body.
Volume of Distribution (V) = Total drug in body (mg) / Plasma [drug] (mg/L)

Question 11

Why is knowing VD important?

Answer 11

Allows calculation of the loading dose.

Question 12

Loading dose

Answer 12

An initial dose of a drug that is used to achieve a desired drug level. Loading dose (mg) = Volume of distribution (L) x Target [plasma] (mg/L)

Question 13

Half-Life

Answer 13

Time taken for drug in body to be reduced by half

Question 14

First Order Kinetics

Answer 14

Type of kinetics when a constant percentage of substrate is metabolised per unit time. Half Life will not change by variations in dose. Changes in [plasma] will change the rate at which it is cleared.

Question 15

Zero Order Kinetics

Answer 15

Drug elimination with a constant amount metabolized regardless of drug concentration

Question 16

What does Half-Life determine?

Answer 16

A drugs duration of action after a single dose
Time to reach steady state with constant dosing
Dosing frequency (how often someone needs to take a particular dose)

Question 17

First Pass Effect

Answer 17

Extraction and metabolism of orally ingested drugs before they reach the systemic circulation.

Question 18

What organs contribute to the first pass effect

Answer 18

Largely the Liver, sometimes the gut wall

Question 19

Bioavailability

Answer 19

Percentage of total drug that reaches the systemic circulation.

Question 20

Phase 1 Metabolism

Answer 20

Oxidation, Hydrolysis etc.

Question 21

Phase II Metabolism

Answer 21

Conjugation

Question 22

Saturation Pharmacokinetics

Answer 22

Zero-Order Kinetics. Duration of drug will depend on dose. Relationship between dose and [steady-state] is unpredictable