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L2 pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is ADME?

A
  • Absorption
  • Distribution
  • Metabolism
  • Excretion
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2
Q

What is bulk flow?

A

Movement of blood from a high pressure region to a low pressure region

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3
Q

What is the diffusion coefficient? (2)

A
  • 1/sqrt(molecular weight)
  • Larger molecular weight = slower diffusion
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4
Q

What is pinocytosis?

A

Cell takes in extracellular fluid along with any dissolved molecules

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5
Q

What is the partition coefficient?

A

Describes how well a substance dissolves into water vs oil

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6
Q

What are the properties of a non-polar drug? (3)

A
  • Fast rate of absorption from the gut
  • High penetration of the brain and other tissues
  • Efficient renal elimination
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7
Q

What kind of substance are many drugs?

A

Weak acids/bases

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8
Q

What is the pKa value for weak acids?

A

Always below 7

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9
Q

What is the pKa value for weak bases?

A

Always above 7

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10
Q

What form are weak acids in at low pH?

A

Un-ionized form (i.e. associated)

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11
Q

In which form can weak acids/bases cross lipid membranes?

A

Uncharged (i.e. associated)

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12
Q

What is the Henderson Hasselbalch equation?

A

pKa = pH + log10(HA/A-)

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13
Q

What kind of substance is aspirin?

A

Weak acid

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14
Q

What is ionic trapping?

A

When a substance dissociates into its ionic form in the plasma, it can’t enter cells across the lipid membrane so is trapped and circulated around the body

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15
Q

What reduces excretion of weak acids?

A

Urine acidification

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16
Q

How can you increase the rate of excretion of weak acids from the body?

A

Increase the pH of plasma e.g. sodium bicarbonate causes the drug to be trapped in the plasma in its ionic form

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17
Q

What is the most direct route of drug administration?

A

Intravenous injection

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18
Q

What is an intrathecal injection?

A

Injection into the spinal chord

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19
Q

What is percutaneous administration?

A

Application of medication to the skin for absorption

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20
Q

What is the most common route of administration?

A

Oral

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21
Q

Why can the rectal route be favourable over the oral route?

A
  • Avoids the issue of the portal blood system from the gut to the liver
  • Drug sent to the liver from the gut, metabolised and excreted via the kidneys
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22
Q

What is bioavailability?

A

Fraction of ingested does which gains access to the circulation

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23
Q

What are the factors affecting absorption? (5)

A
  • Site/method of administration
  • Molecular weight (diffusion rate)
  • Lipid solubility
  • pH and ionisation
  • Transporters available
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24
Q

What is metformin used for?

A

Type 2 diabetes

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25
Q

What are the major body compartments? (4)

A
  • Extracellular fluid
  • Intracellular fluid
  • Transcellular fluid
  • Fat
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26
Q

What is included in extracellular fluid? (3)

A
  • Plasma
  • Interstitial fluid
  • Lymph
27
Q

What is transcellular fluid?

A

Fluids contained with epithelial-lined spaces e.g. CSF, endolymph and perilymph in the ear, fluid in the eyes

28
Q

Which body compartments are water compartments? (3)

A
  • Extracellular fluid
  • Intracellular fluid
  • Transcellular fluid
29
Q

What is the Volume of Distribution (Vd)?

A
  • Vd is the volume of fluid that would be required to hold the concentration of drug in the plasma if it was throughout the body at the same concentration
  • Measure of drug distribution throughout the body compartments
30
Q

How do you calculate Vd?

A

Vd = dose / concentration in the plasma

31
Q

What does high Vd indicate?

A

The drug is well distributed throughout the body tissues and not much stays in the plasma

32
Q

What does low Vd indicate?

A

The drug mainly stays trapped in the plasma and isn’t distributed to body tissues very much

33
Q

What is the Blood-Brain Barrier?

A

The endothelial cells lining blood vessels are joined by tight junctions which prevents large/water soluble molecules passing through

34
Q

What can cross the Blood-Brain Barrier?

A

Lipid soluble molecules

35
Q

How is meningitis treated?

A
  • IV penicillin
  • Antibiotics usually can’t cross the Blood-Brain Barrier but inflammation caused by meningitis causes the tight junctions to be leaky so penicillin can enter the brain to kill the bacteria
36
Q

What is the main protein in plasma?

A

Albumin

37
Q

What kind of drug binds to albumin in plasma?

A

Acidic drugs (anionic)

38
Q

How does binding to plasma protein impact drug distribution? (3)

A
  • Drug bound to protein can’t diffuse into tissues/act on receptors
  • Plasma concentration of the drug would appear lower because bound to protein so not ‘free’
  • Can cause unexpected large increases in drug concentration when all the plasma protein is saturated with drug
39
Q

How does lipid solubility impact drug distribution? (2)

A
  • Lipophilic drugs accumulate in body fat and stay in the body for longer
  • Less of the drug in the plasma membrane of the body cells so the effect is ‘diluted’
40
Q

What is the pH of compartments where weak acids accumulate?

A

High pH (alkaline)

41
Q

What is the pH of compartments where weak bases accumulate?

A

Low pH (acidic)

42
Q

Where in the body does metabolism take place for most drugs?

A

Liver

43
Q

What are the 2 phases of metabolism in the liver

A
  • Phase 1 catabolic reactions
  • Phase 2 synthetic (anabolic) reactions
44
Q

Which enzymes are involved in drug metabolism?

A
  • Microsomal enzymes
  • Intracellular so drug must cross the plasma membrane to be metabolised
45
Q

What is the largest family of enzymes involved in drug metabolism?

A

Cytochrome P450

46
Q

What happens in phase 1 of drug metabolism?

A

The catabolic reactions can produce a more reactive compound

47
Q

What happens in phase 2 of drug metabolism?

A

The anabolic reactions combine the reactive compound with other molecules to form a larger and inactive product

48
Q

What are pro-drugs?

A

Only become active after they’ve undergone phase 1 metabolism

49
Q

How can bile interfere with drug metabolism?

A
  • Drugs administered orally may go straight to the liver from the gut via the portal system and be bound up by bile
  • The bile with the drug is then secreted into the gut again and the drug is lost in the faeces without being metabolised/having its effect
50
Q

How is aspirin eliminated from the body? (3)

A
  • Phase 1 converts aspirin to salicylic acid
  • Phase 2 conjugates the salicylic acid to glucuronide
  • End product re-enters the plasma and is taken to the kidneys for excretion
51
Q

Which environmental factors can interfere with drug metabolism? (2)

A
  • Grapefruit juice can inhibit some cytochrome P450 enzymes
  • Brussel sprouts can induce some cytochrome P450 enzymes
52
Q

What determines which P450 enzyme will be metabolising a drug?

A

Chemical structure of the drug rather than its pharmacological family e.g. paracetamol metabolised by a different enzyme to the other NSAIDs

53
Q

What effect do P450 inducers have?

A

Induce metabolism which can lower the plasma concentration of the drug to a point where it doesn’t achieve its therapeutic effects

54
Q

Why are lipophilic drugs not well excreted by the kidney?

A

If they are lipophilic they will just as easily leave the kidney cells as re-enter them so the phase 2 reactions are important to combine them with something that will facilitate excretion

55
Q

What are the 3 mechanisms of renal excretion?

A
  • Glomerular filtration
  • Active tubular secretion
  • Passive diffusion
56
Q

How can drugs be excreted via glomerular filtration?

A

If they have a small molecular weight after conjugation (<20kDa) they can be filtered at the glomerulus and enter the filtrate to be excreted

57
Q

How can drugs be excreted via active tubular secretion?

A

Most widely used method for excretion of weak acids/bases via transporters

58
Q

How can drugs be excreted via passive diffusion?

A
  • Method used by lipophilic drugs, diffusion across the renal epithelium
  • Not very efficient
59
Q

How is penicillin excreted?

A

Active tubular secretion

60
Q

What are the 3 methods of drug excretion?

A
  • Renal excretion
  • GI excretion (bind to bile)
  • Lung excretion (expired air)
61
Q

What is the t 1/2 value?

A

Time it takes for the plasma concentration of a drug to reduce by 50% (half life)

62
Q

What is Kel?

A

Elimination rate constant

63
Q

What shape does the time course of drug elimination follow?

A

Mono-exponential decay

64
Q

What is saturation kinetics?

A

When the dose overwhelms the systems involved in metabolism/excretion of the drug so plasma concentration increases linearly with each dose instead of reaching a steady state and can causes toxicity e.g. alcohol dehydrogenase and excessive alcohol consumption

L2 pharmacology (9 decks)

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