Pharmacokinetics

Question 1

What is pharmocokinetics?

Answer 1

What the body does to a drug over time

Question 2

Why are pharmocokinetics important?

Answer 2

• looking at the safe dosage for humans

Question 3

What is the conc of drug in the body put simply?

Answer 3

C=Q (known quantity of drug) / Volume

Question 4

What are the steps in pharmacokinetics?

Answer 4

absorption
distribution
metabolism
excretion

Question 5

What do the absorption and distribution determine

Answer 5

how much drug reaches the target per unit time

Question 6

what do metabolism and excretion determine

Answer 6

how much drug is removed from the target site per unit time

Question 7

What does the total body water include

Answer 7

plasma, interstitial fluid and intracellular fluid

Question 8

What are the different delivery methods?

Answer 8

Intravenous
Intramuscular
Oral
Rectal
Inhilation
Transdermal

Question 9

The path of a drug in oral delivery

Answer 9

stomach > epitheium of GI mucosa >vascular endothelium > plasma

Question 10

How do drugs cross cell membranes?

Answer 10

Diffusing through membrane
Diffusing through aqueous channels
Through membrane transporters
Pinocytosis

Question 11

Which drugs diffuse most easily?

Answer 11

lipid soluble

Question 12

What determines solubility ?

Answer 12

Ionisation

Question 13

unionised form of acids

Answer 13

Ha
lipid soluble
can cross membranes

Question 14

ionised form of acids

Answer 14

A-
not lipid soluble
need a transport mechanism

Question 15

pKa

Answer 15

The pH at which 50% of the drug will be ionised and 50% will be protonated

Question 16

pH

Answer 16

pH of the environment in which the drug is dissolved

Question 17

What acids are best at travelling across the cell membrane?

Answer 17

Protonated acids

Question 18

Lower pH

Answer 18

More aspirin in protonated form
more aspirin crosses the cell membrane

Question 19

Aspirin in the stomach

Answer 19

pH is lower than pKa
more aspirin in protonated state
can cross cell membrane into blood

Question 20

Aspirin in plasma

Answer 20

pH is 7.4
More aspirin is in ionised state
low crossing of cell membrane which is what you want

Question 21

Aspirin not absorbed in the stomach moves to the gut

Answer 21

pH is 6
which means more ionised aspirin
low amount of plasma crossing

Question 22

What is distribution ?

Answer 22

Drugs moving between fluid compartments in the body

Question 23

the drugs can exist in

Answer 23

bound or free form

Question 24

Which molecules can move between compartments?

Answer 24

free

Question 25

Why cant a drug get through the blood brain barrier

Answer 25

There are no gaps

Question 26

in BBB what do molecules need to do

Answer 26

pass through endothelial cells

Question 27

What are the ways something can cross BBB

Answer 27

- Passive Diffusion - Carrier-Mediated Transport - Active Transport - Receptor-Mediated Transcytosis - Ion Channels and Exchangers - Drugs that increase permeability

Question 28

Metabolism

Answer 28

phase one and phase two reactions

Question 29

What is phase one metabolism

Answer 29

introduction of a reactive group

Question 30

what is phase two

Answer 30

addition of something this product is usually less active and more water soluble

Question 31

Excretion

Answer 31

this is the removal of the drug from the body

Question 32

What are the stages of excretion?

Answer 32

- Glomerular filtration - Passive reabsorption - Active tubular secretion

Question 33

Glomerular filtration

Answer 33

molecules of MW below 20kDa pass through easily

Question 34

passive reabsorption

Answer 34

Some drugs may pass back into the plasma because of their lipid solubility. Ionised drugs cant be easily reabsorbed.

Question 35

Active tubular secretion

Answer 35

Around 80% of renal plasma flow passes into peritubular capillaries. Drugs can pass from capallaries to tubule via transporters. The secretion is an active process.

Question 36

Total clearance

Answer 36

sum of all methods of drug removal; metabolic clearance, renal clearance, other ways like breathing

Question 37

Rate of drug elimination

Answer 37

plasma concentration x total clearance

Question 38

First order kinetics

Answer 38

- inverse of absorption - clearance related to plasma concentration - concentration of drug is limiting factor

Question 39

Zero order kinetics

Answer 39

- This is when clearance is independant of plasma concentration - limiting factor could be enzyme availability

Question 40

What factors effect the half life of a drug

Answer 40

- type of enzyme - enzyme introduction - enzyme inhibition - enzyme competition - metabolic variability between patients