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Semester 5 - CPT > Pharmacokinetics + Pharmacodynamics > Flashcards

Pharmacokinetics + Pharmacodynamics Flashcards

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1
Q

Define zero order elimination:

A

Constant amount of drug eliminated per unit time = Non-linear (conc of reagent has no effect on reaction rate)

  • Cannot calculate half-life
  • Unpredictable
  • Dangerous
  • Require careful monitoring
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2
Q

Define first order elimination:

A

Constant fraction of drug eliminated = Linear (^conc of reagent = ^reaction rate)

  • Can calculate half-life
  • Predictable
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3
Q

Define oral bioavailability:

A

The fraction of an oral administered drug that reaches systemic circulation.

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4
Q

What factors can affect the oral bioavailability of a drug?

A
  • Drug formulation
  • Age
  • Food (lipid-/water-soluble)
  • Vomiting/malabsorption
  • 1st pass metabolism
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5
Q

Define ‘distribution’ of a drug:

A

The ability of a drug to move between compartments within the body

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6
Q

The distribution of a drug is determined by which factors?

A
  • Protein binding

- Volume of distribution of the drug

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7
Q

What factors affect the protein binding of a drug?

A
  • Hypoalbinaemia
  • Pregnancy
  • Renal failure
  • Displacement by other drugs (precipitant drugs)
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8
Q

How do you calculate the volume of distribution of a drug?

A

Dose / Peak plasma conc of drug (@ time = zero)

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9
Q

In a typical 70kg man, how many litres of fluid is in each compartment?

A
  • Intracellular = 23 L
  • Intravascular = 5 L
  • Interstitial = 14 L
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10
Q

The tissue distribution of a drug can be influenced by what factors?

A
  • Disease states
  • Lipid solubility
  • Active transport
  • Regional blood flow
  • Specific receptor sites in tissues
  • Drug interactions
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11
Q

Which phase of metabolism is dependent on the activity of the CYP450 enzymes?

A

Phase 1

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12
Q

Phase 1 of metabolism is dependent on which enzyme?

A

CYP450

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13
Q

How does a CYP450 inducer affect the activity of other drugs metabolised by this enzyme?

A

A CYP450 inducer would REDUCE the activity of other drugs metabolised by this enzyme
- EXCEPT PRODRUGS - an inducer will cause exaggerated effects of prodrugs

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14
Q

Name some CYP450 inducers:

A
  • Phenytoin
  • Carbamazepine
  • Barbiturates
  • Rifampicin
  • Chronic alcohol use
  • Sulphonylureas
  • St Johns Wort
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15
Q

How does a CYP450 inhibitor affect the activity of other drugs metabolised by this enzyme?

A

A CYP450 inhibitor would INCREASE the activity of other drugs metabolised by this enzyme
- EXCEPT PRODRUGS - an inhibitor will cause reduced activity of prodrugs

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16
Q

Name some CYP450 inhibitors:

A
  • Erythromycin
  • Omeprazole
  • Cimetidine
  • Grapefruit juice
  • Disulfiram
  • Amiodarone
  • Co-trimoxazole
  • Sodium valproate
  • Isoniazid
  • Ciprofloxacin
  • Sulphonamides
  • Amiodarone
  • Fluconazole
  • Fluoxetine
  • Paroxetine
  • Metronidazole
  • Ritonavir
  • Co-trimoxazole
  • Clarithromycin
  • Diltiazem
  • Itraconazole
  • Ketoconazole
  • Nefazodone
  • Telithromycin
  • Verapamil
17
Q

Generally, what can affect the activity of CYP450 enzymes?

A
  • Enzyme inducers
  • Enzyme inhibitors
  • Age
  • Liver disease
  • Hepatic blood flow
  • Cigarette consumption
  • Alcohol consumption
18
Q

Where in the body can you find CYP450 enzymes?

A
  • Liver (mainly)
  • Gut
  • Lung
19
Q

Describe phase II metabolism:

A

Conjugation with a polar molecule to make drug water soluble, enabling rapid elimination
- conjugation with glutathione, glucoronic acid, sulphate, or N-acetyl

20
Q

What are the possible routes of drug elimination?

A
  • Kidney
  • Lungs
  • Sweat
  • Tears
  • Breast milk
  • Genital secretions
  • Bile
  • Saliva
21
Q

What factors determine the renal excretion of drugs?

A

1) GFR - filtration of unbound drugs ie Gentamycin
2) Active tubular secretion ie Penicillin
3) Passive tubular reabsorption ie Aspirin

22
Q

Define drug clearance:

A

The ability to excrete the drug, mostly = GFR

23
Q

What is the relationship between clearance and half-life of a drug?

A

Half-life is inversely proportional to clearance

- As clearance decreases, half-life increases

24
Q

Which of zero order and first order elimination can be saturated?

A

Zero order

Constant amount of drug eliminated = non-linear

25
Q

Within how many half-lives is a new steady state of [drug] in plasma achieved? (if first order kinetics)

A

3-5 half lives

Irrespective of dose or frequency

26
Q

Define drug selectivity:

A

How selective a drug is for its target

27
Q

Define drug specificity:

A

How specific a drug is to its subtype receptor or tissue

28
Q

Define efficacy:

A

The ability of a drug to produce a response as a result of the receptor being occupied

29
Q

Define potency:

A

The dose required to produce the desired biological response

- The smaller the dose required, the higher the potency

30
Q

Define therapeutic index:

A

The therapeutic index of a drug is the ratio of the lethal dose to the effective dose, used in assessing the safety of a drug.

  • Barbiturates have a narrow therapeutic index between the dose required for effect and the dose that will cause death.
  • The larger the therapeutic index, the safer the drug
31
Q

List some common potent drugs which have a low therapeutic index:

A
  • Warfarin
  • Gentamicin
  • Digoxin
  • Lithium
  • Theophylline
  • Phenytoin
  • Amphotericin B
  • 5-fluorouracil
32
Q

Define therapeutic window:

A

Therapeutic window is a range of doses that produces therapeutic response without causing any significant adverse effect in patients.
- Paracetamol has a narrow therapeutic window

Semester 5 - CPT (5 decks)

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