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Semester 2 Pharmacology > Pharmacokinetics 2 > Flashcards

Pharmacokinetics 2 Flashcards

1
Q

Describe the two phases of metabolism in the liver

A

Phase 1:
• Generally oxidation, reduction or hydrolysis
- Introduce/reveal a reactive chemical group
• Products are often more reactive

Phase 2:
• Synthetic, conjugative reactions
• Makes it more hydrophilic (transport more dependent on carrier transport which is more selective, so more likely to get rid of it), inactive compounds generated

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2
Q

What are the functions of cytochrome P450 enzymes?

A
  • Biosynthesis of steroids, fatty acids and bile acids

* Metabolism of endogenous and exogenous substrates

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3
Q

What are cytochrome P450 enzymes?

A

Mixed function monooxygenases
• Throughout the body, extensively in the liver
• Phase 1 metabolism enzymes
• They can be induced or inhibited

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4
Q

Where does metabolism mainly occur?

A

The liver

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5
Q

Which drugs are eliminated more readily?

A

Hydrophilic over lipophilic (except in the lungs)

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6
Q

What are the possible sources of excretion?

A
  • Breath
  • Urine
  • Saliva
  • Perspiration
  • Feces
  • Milk
  • Bile
  • Hair
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7
Q

What is the most important organ involved in the elimination of drugs and their metabolites?

A

The kidneys

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8
Q

What are the factors that can affect pharmacokinetic parameters?

A
  • Age
  • Sex
  • Pregnancy
  • Body weight
  • Genetic variability
  • Diet
  • Disease
  • Other medications
  • Ethnicity
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9
Q

Describe the onset, duration and metabolism of vecuronium

A

Onset: medium

Duration: medium

Metabolism: Liver- eliminated via the urine and bile

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10
Q

Describe the onset, duration and metabolism of atracurium

A

Onset: medium

Duration: medium

Metabolism: Spontaneous degradation in the plasma

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11
Q

Describe the onset, duration and metabolism of mivacurium

A

Onset: Fast

Duration: Short

metabolism: Plasma cholinesterase

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12
Q

Describe enterohepatic recirculation of drugs

A

• Hydrophobic drug molecule enters the liver
(• Hydrophilic metabolite)
• Conjugate form of the drug
• Passes out in the bile
• Travels to the intestine
• De-conjugation and re-uptake
• Re-enters the liver and in conjugate form
• Repeats
- Increases the duration of action
- Dependent on gut biota
- Become less effective if on antibiotics

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13
Q

Describe the metabolism of paracetamol

A

• Majority is conjugated with glucoronide
• Then most of the rest is conjugated with sulphate
• The rest is converted to a toxic metabolite by cytochrome P450 then:
If there are normal glutathione levels:
• Conjugated with glutathione then excreted
If the glutathione levels are reduced:
• Combined with hepatic proteins
• Leads to toxicity of the liver

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14
Q

Which drug can decrease the effect of warfarin and why?

A

Phenobarbital by increasing the expression of CYP450s which is what warfarin is metabolised by

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15
Q

What is the effect of grapefruit juice on CYP450s?

A

They inhibit CYP450s (mainly in the gut)

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16
Q

Describe the interaction between grapefruit and simvastatins

A
  • Simvastatins are metabolised by CYP3A4 in the gut wall and the liver
  • Increases the plasma concentration
17
Q

In the lungs, what characteristic of drug is more likely to be exhaled?

A
  • Lipophilic

* Volatile

18
Q

What is minimum effective concentration?

A

The minimum plasma concentration that needs to be achieved before evidence of a the therapeutic effect could be observed.
For some drugs the longer you keep above this concentration the better

19
Q

How is minimum effective concentration measured?

A

• Dose escalation trials and relating the plasma concentration to observed effect

20
Q

What is minimum toxic concentration?

A

The minimum plasma concentration required to observe unwanted or toxic effects of the drug. Avoiding being above this level is favourable

21
Q

What is the therapeutic window?

A

The gap between the minimum effective concentration and the minimum concentration that has unwanted side effects (toxicity)

22
Q

What is meant by a closed therapeutic window?

A

When the therapeutic window is closed, you can’t separate toxicity from clinical use

23
Q

How do you calculate the therapeutic window?

A
  • Drug plasma concentration graph

* Draw a horizontal line alone the minimum effective concentration and another along the minimum toxic concentration

24
Q

What is the onset of action?

A

How long it takes your drug plasma concentration to reach the ‘minimum effective concentration’ following administration

25
Q

How do you calculate onset of action?

A
  • Draw a horizontal line along the minimum effective concentration
  • Onset will be the time at which your drug plasma concentration curve breaches that line
26
Q

What is duration of action?

A

How long evidence of a drug’s pharmacological action remains evident

27
Q

How do you calculate duration of action?

A
  • Draw a horizontal line along the minimum effective concentration
  • Mark the time at which the drug plasma concentration curve breaches the line and when the curve descends back below the line
  • The time between is the duration of action
28
Q

What is Cmax?

A

The peak plasma concentration achieved after administration of a drug

29
Q

How do you calculate C max?

A

Extrapolate horizontally from the highest point on your drug plasma concentration graph

30
Q

What is Tmax?

A

The time taken to reach Cmax

31
Q

How do you calculate T max?

A

• Extrapolate vertically down from the highest point on the drug plasma concentration graph

32
Q

What can absorption half life be used for?

A
  • To predict Tmax

* If absorption half life increases, you would expect T max to take longer to reach

33
Q

What is plasma clearance half life?

A
  • Independent on drug preparation and formulation

* Used to predict how long it will take for the drug to be removed from the body

34
Q

How do you calculate Plasma clearance half life?

A
  • Identify Cmax and Tmax
  • Start at T max and work towards the right and work out how long it takes for 50% of Cmax to be reached
  • The duration of this time between these two points is the half life

Semester 2 Pharmacology (11 decks)

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