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Fundamentals Of Pharmacology And Physiology > Drug Metabolism And Elimination > Flashcards

Drug Metabolism And Elimination Flashcards

1
Q

What is drug metabolism?

A

Removal of lipid soluble drug molecules to prevent reabsorption by kidneys

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2
Q

How is drug metabolism achieved?

A

Converting drugs into water soluble molecules

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3
Q

Where does drug metabolism take place?

A

Mostly in liver, but also in plasma, long and intestinal epithelium

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4
Q

What is excretion?

A

Removal of drugs/ metabolites from the body

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5
Q

Where are drugs excreted (8)?

A

Mostly in urine, but also bile, faeces, sweat, tears, saliva, exhaled air and milk (more lipid soluble drugs)

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6
Q

What is drug clearance?

A

The volume of plasma cleared of drug per unit time

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7
Q

What is the formula of clearance for a drug that is removed by liver metabolism and kidney excretion?

A

Plasma clearance = hepatic clearance + renal clearance

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8
Q

What does it mean if a drug has a high plasma clearance?

A

The body’s more capable of removing it (and usually has a smaller half life too)

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9
Q

What determines the amount of drug available at the site of action?

A

Metabolism and plasma clearance

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10
Q

What affects the time between doses?

A

Time taken for a drug to reach steady state levels

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11
Q

What safety issues are there with drugs?

A

Metabolism produces new chemical entities that may have their own effects
Components of racemic molecules handled differently

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12
Q

What is a prodrug?

A

Drugs that are activated by metabolism

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13
Q

Give an example of a prodrug, with the product and the facilitating enzyme

A

Enalapril -> enalaprilat by esterases

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14
Q

When does drug removal begin?

A

Immediately

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15
Q

What do most drugs undergo to increase excretion?

A

Metabolism

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16
Q

What happens if theres a loss of or reduced biological activity when a drug is metabolised?

A

Increase polarity/ less receptor binding

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17
Q

Give an example of a drug that is eliminated without being metabolised

A

Digoxin

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18
Q

Why would you use prodrugs(4)?

A

better pharmacokinetic profile
orally available
More Readily absorbed
Better bioavailability

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19
Q

What are the two phases of drug metabolism?

A

Phase 1 and 2

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20
Q

What does phase 1 of drug metabolism include?

A

Introduces chemically reactive groups

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21
Q

What does phase 2 of drug metabolism include?

A

Increases water solubility of drug for excretion

22
Q

What processes happen in phase 1 of drug metabolism?

A
  • oxidation in the liver

- addition of oxygen molecules to carbon, nitrogen, sulfur molecules in drug structure

23
Q

What is phase 1 of drug metabolism carried out by?

A

Cytochrome P450 enzymes

24
Q

What do cytochrome P450 enzymes do?

A

Binds molecular oxygen to the drug

The other oxygen is reduced to water

25
Q

What happens in phase 2 of drug metabolism?

A

Adds the phase 1 product to an endogenous substance through the production of stable covalent bonds

26
Q

Give an example of the phase 2 in drug metabolism

A

Glucuronidatoin

27
Q

What is glucuronidation?

A

Phase 2 reaction with glucose

28
Q

What is the exception to the phase 1/2 scheme?

A

Paracetamol

29
Q

Through which phase is paracetamol more readily metabolised?

A

Phase 2

30
Q

What are the two phase 2 reactions that paracetamol could undergo?

A

Glucuronidation

Sulfate conjunction

31
Q

What is glucuronidation?

A

The addition of a glucose molecule

32
Q

When do phase 2 reactions not happen on paracetamol?

A

When you run out of glucose, sulfate and enzymes

33
Q

What happens if the phase 2 enzymes in paracetamol metabolism are saturated?

A

A phase 1 reaction happens - cytochrome p450

34
Q

What does paracetamol and cytochrome p450 make?

A

Quinone

35
Q

What can make quinone safe and water soluble?

A

Glutathione

36
Q

What does the amount excreted through the glomerulus depend on?

A

The levels of drug bound to plasma proteins

37
Q

What sized molecules does glomerulus filtration filter?

A

<20kDa

38
Q

How does reabsorption happen in the kidneys?

A
  • molecules pass through tubules, becoming more concentrated.
  • this creates a large conc grad for reabsorption
39
Q

Why do drugs need to be water soluble?

A

To allow them to be reabsorbed

40
Q

How does tubular secretion work?

A
  • Acid/base molecule carries transposing molecules into tubular fluids
  • lower levels of unbound drug in plasma, pushing reaction for plasma proteins to release more free drug for secretion by carriers
41
Q

Give the formula for excretion that includes filtration, secretion and reabsorption

A

Excretion= filtration - reabsorption + secretion

42
Q

What is renal clearance?

A

The volume of plasma cleared of drug per unit time in one pass through the kidney

43
Q

Where does the drug go once it is cleared from the blood?

A

Urine

44
Q

What does decreased renal elimination lead to?

A

Increased plasma half life

45
Q

What are the four factors that affect drug metabolism and excretion?

A

Age, genetics, drug metabolising enzymes and disease

46
Q

How does age affect drug metabolism and excretion?

A
  • Cytochrome P450 activity and GFR reduced in neonates/ the elderly
  • increased to fat content in elderly
47
Q

How does genetics affect drug metabolism and excretion?

A

45% in Europe and USA as a pose to 80-90% in Asians fast acetylators

1/3000 slow metabolism by pseudocholinesterase

48
Q

How do drug metabolising enzymes affect drug metabolism and excretion?

A

Can be induced or inhibited by other drugs or lifestyle factors

Eg taken with a specific food/ at a certain time of day

49
Q

How does disease affect drug metabolism and excretion?

A

Liver disease impairs drug metabolism- drug toxicity

Renal disease may alter pharmacokinetics

50
Q

Why would you need to monitor drug concentrations (7)?

A
  • drugs that have a narrow therapeutic index
  • drugs that relate well to either theraputic effect or toxic effect, or both
  • to individualise therapy
  • to confirm adherence of therapy
  • to diagnose toxicity
  • to determine the presence of other drugs before starting therapy
  • as part of post marketing surveillance to drug-drug interaction

Fundamentals Of Pharmacology And Physiology (7 decks)

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