Pharmacokinetics and drug metabolism

Question 1

What are the 4 stages of a drugs journey through the body?

Answer 1

Absorption
Distribution
Metabolism
Excretion

Question 2

What are the possible ways of administering drugs?

Answer 2

Ingestion
Dermal
Intramuscular
Subcutaneous
Intraperitoneal
Intravenous
Inhalation

Question 3

What is a systemic drug and give a common example?

Answer 3

Affects entire organism and aspirin

Question 4

What is a local drug and give a common example?

Answer 4

Restricted to one area of the organism and salbutamol

Question 5

What is an enteral drug and give a common example?

Answer 5

Gastro-intestinal administration

Question 6

What are the two ways that drugs move around the body?

Answer 6

Bulk flow transfer e.g. bloodstream

Diffusional transfer e.g. molecule by molecule over short distance

Question 7

What are the compartments and barriers that drugs have to traverse?

Answer 7

Compartments= aqueous e.g. blood, lymph, extracellular fluid and intracellular fluid
Barriers= Lipid e.g. cell membranes (epithelium/endothelium)

Question 8

How can drugs cross these barriers?

Answer 8

Diffusing through lipid
Carrier molecules
Diffusing through aqueous pores in lipid
Pinocytosis

Question 9

How do most drugs exist?

Answer 9

Weak acids (ionised) or weak bases (non-ionised)

Question 10

What is the difference between ionised and non-ionised drugs?

Answer 10

Non ionised/non polar can freely dissolve in non-polar substances e.g. penetrate lipid membranes freely

Question 11

What factors affect drug distribution?

Answer 11

Regional blood flow
Extracellular binding (plasma proteins)
Capillary permeability
Localisation in tissues

Question 12

How does metabolism affect blood flow?

Answer 12

Higher metabolically active tissues lead to denser capillary networks

Question 13

What percentage of acidic drugs are plasma protein bound?

Answer 13

50-80%

Question 14

What are the two major routes of drug excretion?

Answer 14

Kidney- responsible for elimination of most drugs

Liver- Some drugs are concentrated in bile

Question 15

What happens to drug-protein complexes when they reach the glomerulus?

Answer 15

They are not filtered

Question 16

What happens at the proximal tubule in terms of excretion?

Answer 16

There is active secretion of acids and bases

Question 17

What happens at the proximal and distal tubules in terms of reabsorption?

Answer 17

Lipid soluble drugs are reabsorbed

Question 18

How does treatment with intravenous sodium bicarbonate increase aspirin excretion?

Answer 18

It increases urine pH which ionises the aspirin making it less lipid soluble and less reabsorbed from the tubule increasing its rate of excretion

Question 19

Apart from the two main routes, what other routes of excretion are there?

Answer 19

Lungs
Skin
Gastrointestinal secretions
Saliva
Sweat
Milk
Genital secretions

Question 20

What is bioavailability?

Answer 20

Proportion of administered drug that is available within the body to exert its pharmacological effect

Question 21

What is the apparent volume of distribution?

Answer 21

The volume in which a drug appears to be distributed- an indicator of the pattern of distribution

Question 22

What is biological half life?

Answer 22

The time taken for the concentration of the drug in the blood to fall to half its original value

Question 23

What is clearance?

Answer 23

Blood clearance is the volume of blood cleared of a drug in a unit time

Question 24

What is first order kinetics?

Answer 24

The rate of elimination of a drug where the amount of drug decreases at a rate that is proportional to the concentration of drug remaining in the body

Question 25

What is the volume of distribution?

Answer 25

Dose divided by the initial concentration of the drug in the plasma

Question 26

What is zero order kinetics?

Answer 26

A constant amount of drug is removed per unit time (something is saturating the rate of removal, usually an enzyme)

Question 27

What common sort of drug follows zero order kinetics?

Answer 27

Alcohol

Question 28

What kinetics do most drugs follow?

Answer 28

First order