Pharmacokinetics Explaination

Question 1

What is the first pass effect?

Answer 1

where a significant portion of the (orally administered) drug is metabolised by the liver before it reaches systemic circulation

Question 2

What is bioavalibility?

Answer 2

• the amount of the drug that reaches systemic circulation in an unchanged form and becomes available for biological effect after administration (from any route)

Question 3

What is half life?

Answer 3

the rate of elimination (the time for drug concentration in the blood to half)

Question 4

What are the 6 routes of administration and their sites of absorption?

Answer 4

• oral (mouth, GI tract)
• inhalation (nasal passage or lungs)
• intravenous (IV) (directly into venous blood)
• intramuscular (directly into muscle)
• transdermal (skin)
• buccal (oral mucosa)

Question 5

What is drug absorption?

Answer 5

the movement of the drug into the blood stream where it must cross a series of membranes

Question 6

5 common modes of transport in drug absorption

Answer 6

• filtration through pores
• passive diffusion through the membrane
• active transport
• facilitated diffusion
• phago/pinocytosis

Question 7

What is the route of absorption - oral to blood?

Answer 7

GI tract, liver, right heart, lungs, left heart, arterial circulation

Question 8

What is the route of absorption - inhalation to blood?

Answer 8

lungs, left heart, arterial circulation

Question 9

What is the route of absorption - buccal to blood?

Answer 9

oral mucosa, venous circulation, right heart, lungs, left heart, arterial circulation

Question 10

What is the route of absorption - transdermal to blood?

Answer 10

skin absorption, venous circulation, right heart, lungs, left heart, arterial circulation

Question 11

What is the route of absorption - intramuscular to blood?

Answer 11

muscle tissue, muscle capillaries, venous circulation, right heart, lungs, left heart, arterial circulation

Question 12

What is the bioavalibility of intravenous administration?

Answer 12

100%

Question 13

What is metabolism?

Answer 13

• biochemical modification or degradation through specialised enzymatic actions (2 phases)

Question 14

What are the 2 phases of metabolism?

Answer 14

1) non-synthetic, 2) synthetic

Question 15

What does phase 1 metabolism involve?

Answer 15

non-synthetic reactions that break down existing bonds in the drug’s molecules

Question 16

What do phase 1 metabolism reactions result in?

Answer 16

alters the drug’s structure without creating new bonds, influencing its pharmacological activity or facilitating further metabolism

Question 17

What does phase 2 metabolism involve?

Answer 17

synthetic bonds that form new chemical bonds to create drug metabolites

Question 18

What do phase 2 metabolism reactions often result in?

Answer 18

the formation of more water-soluble metabolites

Question 19

What is the benefit of a substance being more water-soluble?

Answer 19

easier to excrete, aiding in their elimination

Question 20

What are the 5 types of reactions in phase 1 metabolism?

Answer 20

• hydrolysis
• oxidation
• reduction
• dealkylation
• deacetylation

Question 21

What are the 4 types of reactions in phase 2 metabolism?

Answer 21

• sulphation
• glucuronidation
• acetylation
• amino acid conjugation

Question 22

What is half life and clearance used for?

Answer 22

To quantify the rate and extent of the drug removal from the body

Question 23

What are most drugs metabolised to?

Answer 23

water soluble substances, whhich are excreted in urine

Question 24

If a drug can only be metabolised into lipid soluble compounds, where are they excreted?

Answer 24

in the bile, through the large intestine (in the faeces)

Question 25

Where does most metabolism occur?

Answer 25

In the liver, often catalysed by CYP450 enzymes

Question 26

What is catabolism?

Answer 26

the process of breaking down molecules into smaller units

Question 27

what are the steps of the first pass effect?

Answer 27

• dissolve in stomach’s gastric juices
• diffusion into blood stream from intestine
• delivery to liver by hepatic portal vein
• processing by the liver (may involve metabolism)
• delivery to systemic circulation

Question 28

What result does the first pass effect have?

Answer 28

the oral bioavailability of the drug reduced

Question 29

Name 5 factors that affect the rate and extent of drug distribusion

Answer 29

• chemical structure of drug
• route of administration
• presence of food/drugs in GI tract
• stability of the drug in the GI tract (if oral route)
• ease of transport through membranes (like BBB)

Question 30

How is the extent of distribution expressed?

Answer 30

the volum of distribution (total amount of drug present in the body/concentration in blood plasma)

Question 31

What does a high volume of distribution value correspond to?

Answer 31

extensive distribution in the peripheral tissue

Question 32

What factors can cause half life values to vary?

Answer 32

patient and drug specific values like liver or kidney failure

Question 33

What is the theraputic index?

Answer 33

the difference between the theraputic effect and toxic effect in 50% of people

Question 34

What is the time range for drug detection in blood, urine, and hair?

Answer 34

• blood = hours to days
• urine = days to weeks
• hair = days to months

Question 35

What does urine testing show? Name 3 methods of testing

Answer 35

indicate the presence of the drug and common metabolites
- immunoassays
- simple colour change tests
- chromatography

Question 36

What can support defence in law regarding BAC?

Answer 36

• witness statements
• estimate of BAC by expert witness

Question 37

What can support defence in law regarding BAC - what do calculations of BAC include?

Answer 37

• total ethanol consumed and time of consumption
• weight, general health, and person’s drinking habits
• metabolic rate

Question 38

How is the concentration (g/L) of alcohol in the body determined?

Answer 38

(total alcohol consumed - amount of alcohol metabolised) / volume of distribution

Question 39

How is the mass (g) of alcohol in the body consumed?

Answer 39

(amount of alcohol consumed in ml) x (% ABV) x (density of ethanol: 0.789g/ml)

Question 40

What is the average volume of distribution of ethanol?

Answer 40

0.54 litres/kg of body weight

Question 41

What is the approximate clearance rate of ethanol?

Answer 41

0.12 g/kg of body weight per hour

Question 42

What would increase the clearance of ethanol by 20% and why?

Answer 42

if the person is an experienced drinker, in order to account for induction of the liver enzymes which metabolise alcohol

Question 43

What enzymes does ketamine use for metabolism, and what metabolite does that produce?

Answer 43

CYP450 and CYP3A4, and norketamine

Question 44

Where is ketamine metabolised, eliminated, and excreted?

Answer 44

liver, kidneys, urine