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Clinical Pharmacology and Therapeutics > 1. Pharmacokinetics > Flashcards

1. Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

The study of movement of a drug into and out of the body, ie What the body does to the drug.

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2
Q

What are the 4 processes in pharmacokinetics?

A

ADME - Absorption, Distribution, Metabolism, and Elimination.

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3
Q

What is the therapeutic window?

A

The dose range between the minimum effective dose, and the maximum safely tolerated dose

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4
Q

How is absorption measured?

A

Bioavailability

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5
Q

What does bioavailability depend on?

A

Drug formulation, first pass metabolism, pt age, food, lipid vs water solubility of drug, and V&D/malabsorption.

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6
Q

What is first pass metabolism?

A

Any metabolism that occurs before the drug enters systemic circulation.

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7
Q

Where can first pass metabolism occur?

A

The liver, the gut lumen, or the gut wall.

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8
Q

What factors in the gut lumen can cause first pass metabolism to occur?

A

Gastric acid
Proteolytic enzymes
Foods eg grapefruit juice

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9
Q

What are some examples of drugs that undergo gut lumen first pass metabolism?

A

Insulin
Ciclosporin
Benzylpenicillins

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10
Q

What factors in the gut wall can cause first pass metabolism to occur?

A

P-glycoproteins efflux pumps (remove contents back into lumen)

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11
Q

What are some examples of drugs that undergo gut wall first pass metabolism?

A

Ciclosporin

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12
Q

What factors in the liver can cause first pass metabolism to occur?

A

Inactivation, oxidation, or conjugation. Metabolites can then be sent back to the gut lumen.

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13
Q

Via what can metabolites from the liver be sent back to the gut lumen?

A

The enterohepatic circulation

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14
Q

What are the 2 key factors in distribution of a drug?

A

Protein binding

Volume of distribution

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15
Q

What kind of drugs bind to albumin?

A

Acidic drugs

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16
Q

What kind of drugs bind to globulins?

A

Hormones

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17
Q

What kind of drugs bind to lipoproteins or glycoproteins?

A

Basic drugs

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18
Q

How can protein binding be influenced?

A

Displacement of drugs from proteins by other drugs

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19
Q

What happens when one drug (drug A) is displaced by another from its protein-bound state?

A

Increased amount of free drug A

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20
Q

When can protein binding drug interactions occur?

A

When there is:

  • high protein binding
  • low Vd
  • hyperalbuminaemia
  • pregnancy
  • renal failure
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21
Q

When are protein binding drug interactions important?

A

When the drug has a narrow therapeutic window

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22
Q

What is the volume of distribution?

A

Measurement of how widely a drug is distributed throughout body tissues.

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23
Q

What is the significance of a high Vd?

A

Less drug is available in the blood stream per unit given

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24
Q

Where does drug metabolism chiefly occur in the body? And where else?

A

The Liver!

But also the gut and the lung

25
Q

What are the liver phase 1 enzymes?

A

CYPs

26
Q

What do CYPs do?

A

Oxidation, dealkylation, reduction, and hydrolysis.

27
Q

What does CYPS stand for?

A

Cytochrome P

28
Q

What can happen to metabolites after phase 1? (3)

A
  1. Further processing by phase 2 enzymes (which then do 2 or 3)
  2. Go to Kidney to be excreted in urine
  3. To the gallbladder to be excreted via bile
29
Q

What are active metabolites?

A

Products of metabolism of inactive drugs that are now active

30
Q

Give an example of an inactive drug/active metabolite and its use.

A
  1. L-Dopa (metabolised to dopamine) - Parkinson’s

2. Enalaprilat (to enalapril) - Hypertension

31
Q

What drugs (6) do CYP 450 3A enzymes metabolise?

A 
Ca2+ Channel Blockers
Benzodiazepines
HIV protease inhibitors
Many statins
Cyclosporin 
Antihistamines
32
Q

What inhibits CYP 3A?

A

Antifungals
Cimetidine
Macrolides
Grapefruit

33
Q

What drugs induce CYP 3A?

A 
Carbamazepine
Phenytoin
Rifampicin
Ritonavir
St John’s Wort
34
Q

What does CYP 2D6 metabolise?

A

Codeine
Beta Blockers
Tricyclics

35
Q

What inhibits CYP 2D6?

A

Fluoxetine
Paroxetine
Haloperidol
Quinidine

36
Q

Who is CYP 2D6 absent in?

A

7% of Caucasians

37
Q

Who is CYP 2D6 hyperactive in?

A

30% of East Africans

38
Q

Who is CYP 2C9 absent in?

A

1% of Caucasians and blacks

39
Q

What does CYP 2C9 metabolise?

A

Most NSAIDs
Warfarin
Phenytoin
Tolbutamide

40
Q

What inhibits CYP 2C9?

A

Fluconazole

41
Q

What induces CYP 2C9?

A

Carbamazepine

Ethanol

42
Q

What can influence CYP450 enzymes?

A

Enzyme inducing/inhibiting drugs

43
Q

Where are CYP450 isoenzymes found?

A

Mostly in the liver

44
Q

What % of drug metabolism are CYP450s responsible for?

A

90%

45
Q

How can CYP450 enzymes explain different metabolism of drugs between different pts?

A

Genetic differences in individuals -> different levels of activity of different CYP450 isoenzymes

46
Q

What is the main route of elimination?

A

Kidney

47
Q

What does renal excretion of a drug depend on?

A

Glomerular filtration, passive tubular reabsorption, and active tubular secretion

48
Q

What is GFR proportional to?

A

Excretion of unbound drugs (eg gentimicin)

49
Q

Give an example of a drug that is actively excreted

A

Penicillin

50
Q

What is passive reabsorption influenced by?

A

Urine flow rate, and pH

51
Q

What is clearance and how is it measured?

A

Rate of removal by excretion of a drug from the body. Usually roughy equal to GFR.

52
Q

Define 1st order kinetics

A

Rate of elimination of drug is proportional to drug level ie a constant % of the drug is eliminated

53
Q

Define zero order kinetics

A

Rate of elimination of a drug is constant

54
Q

When can drugs that are usually 1st order bexhibit zero order kinetics?

A

At high doses, when enzymes/pathways etc become saturated

55
Q

What is the issue with drugs that exhibit zero order kinetics?

A

More likely to result in toxicity

56
Q

What 4 main reasons are there for drug monitoring?

A
  1. If the drug has zero order kinetics
  2. If the drug has long t1/2
  3. Narrow therapeutic window
  4. Greater risk of DDIs
57
Q

With repeated administration, after how many half lives is a steady state reached?

A

3-5

58
Q

How many t1/2s dose it tend to take to eliminate a drug?

A

3-5

Clinical Pharmacology and Therapeutics (26 decks)

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