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PODS > Drug pharmokinetics > Flashcards

Drug pharmokinetics Flashcards

1
Q

Where are most drugs absorbed

A

GI tract

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2
Q

Discuss the factors that affect absorption from the GI tract

A

Motility - speed of absorption will affect speed of drug reaches site of action
Food - can enhance or impair rate of absorption
Illness- Malabsorption, migraine reduces the rate of stomach emptying

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3
Q

What site is the most common site of action for drugs

A

Small intestine

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4
Q

Why is the C.dif drug absorbed

A

The lining of the bowel is inflammed

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5
Q

What physio- chemical factors that affect transfer of drugs across the cell membrane

A

Molecular size and shape
Degree of ionisation
Lipid solubility

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6
Q

Do ionised drugs cross the cell membrane

A

NO

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7
Q

What is the degree of ionisation highly dependent on

A

pH of the environment (gut)

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8
Q

Do un-ionised drugs cross the cell membrane

A

yes - distribute until equilibrium is reached

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9
Q

Define bioavailabilty

A

Amount of drug that reaches circulation and is available for action

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10
Q

What factors affect bioavailabilty

A 
Slow release formulation
Ability to pass membrane
GI effects - illness/ food
First pass metabolism
Route of administration
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11
Q

Describe Tmax

A

The time taken for concentration the peak
Higher rate of absorption = faster conc. peak
Dose wont alter

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12
Q

Describe Cmax

A

Increasing drug dose increases peak concentration

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13
Q

Define AUC (area under curve)

A

Amount of drug which reaches the systemic circulation

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14
Q

Define therapeutic range

A

Measure of the range at which a drug is safe and active
Above - toxic
Below - inactive

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15
Q

Define drug distribution

A

The reversible transfer of a drug between the blood and the extra-vascular fluids and tissues of the body

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16
Q

Describe the medical importance of the first pass metabolism

A

Metabolism of drug prior to reaching the systemic circulation
Can limit the oral route
Can be altered by other drugs or disease

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17
Q

What structures are involved in the first pass metabolism

A 
Gut lumen (acid, enzymes)
Gut wall (metabolic enzymes)
Liver (heapatic enzymes)
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18
Q

How do plasma proteins affect the binding of drugs

A

Only unbound drugs are biologically active

19
Q

What does plasma protein binding depend on

A

Renal failure
Malnourishment / low protein
Pregnancy
Other drugs

20
Q

What are the most common plasma proteins drugs bind to

A

albumin and alpha-1-acid glycoprotein

21
Q

What is the lipid; water partition coefficient?

A

Ratio of dissolved drug in lipid and water phase in contact

22
Q

In terms of lipid solubility, what must drugs be to cross the membrane?

A

in solution and lipid soluble

23
Q

What factors affect the therapeutic range of a drug

A

Volume of distribution, Clearance, Half life

24
Q

Describe the Volume of Distribution

A

the volume in which the drug would be uniformly distributed to produce the observed blood concentration
Higher Vd- Greater ability to diffuse across the membrane
Low Vd - Drug will stick to proteins

25
Q

What should the volume of distribution theoretically be?

A

42 L

26
Q

Describe clearance

A

the theoretical volume of fluid from which a drug is completely removed over time
Measure of elimination in ml/min

27
Q

How do renal and hepatic functions affect the clearance of a drug

A

renal - concentration and urine flow

hepatic - metabolism and biliary excretion

28
Q

What will happen if the liver and kidney are failing?

A

Drug will build up leading to toxicity

29
Q

Describe half-life of a drug

A

the time taken for the drug concentration in the blood to decline to half original value
t1/2 = 0.693Vd/C (depends on Vd and C)
Longer half life -> toxicity

30
Q

What does the half life of a drug help to know

A

How often to administer a drug to achieve optimal plasma concentration

31
Q

What is the primary organ of excretion

A

Kidney

32
Q

Describe glomerular filtration (most important excretion route)

A

Glomerular filters all unbound drugs of correct size, charge and shape
If mutated - reduced drug clearance
(filters around 190L a day)

33
Q

Describe the main method of excreting protein bound cationic and anionic drugs

A

Active tubular secretion - drugs are actively secreted into the proximal tubule

34
Q

Describe the passive tubular reabsortption of weak un-ionised drugs

A

As filtrate moves down renal tube, the drug present is concentrated.
Passive diffusion down conc. gradient allows drug to move back into circulation
Occurs in distal tube + collecting duct

35
Q

Define drug metabolism

A

Biochemical modification of pharmaceutical substances by living organisms, usually through specialised enzymatic activity

36
Q

Where does most drug metabolising occur and by which enzymes

A

Liver - cytochrome p450

37
Q

Describe the effects of bile secretion on drug activity

A

Drugs passively or actively secreted into bile for excretion
Many drugs then reabsorbed into the circulation (entero-hepatic circualtion)
Continues until drug is metabolised in liver until excreted by kidney

38
Q

List the factors which affect drug metabolism

A 
Other drugs!! (herbal - enzyme inhibitors)
Genetics
Hepatic blood flow
Age, ethnicity and gender
Pregnancy
Rate of first pass metabolism
39
Q

Which sex is more prone to drug toxicity?

A

Women

40
Q

How does age affect drug metabolism

A

Young - reduced enzyme activity and renal function

Old - Low weight, reduced renal activity, often on multiple drugs due to chronic disease

41
Q

What age range has the greatest metabolizing rate

A

Teenagers

42
Q

Describe the process of drug metabolising

A

Makes lipid soluble/ non polar compounds into water soluble/ polar compounds to be excreted
Can activate to form pro-drugs

43
Q

Describe the reactions involved in the Phase 1 Metabolism and what they do

A

Hydrolysis, Oxidation and reduction
Expose polar groups to provide an active site for phase 2
cytochrome p450 - oxidative

44
Q

Outline the phase 2 metabolism and conjugation

A

Molecule from phase 1, endogeneous to body donates segment to the foreign molecule
Conjugation - increases water solubility, enhancing excretion

PODS (15 decks)

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