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Drug Action > Drug metabolism and excretion > Flashcards

Drug metabolism and excretion Flashcards

1
Q

What is drug elimination?

A

The irreversible removal of the drug from the body

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2
Q

What primarily carries out metabolism?

A

The liver

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3
Q

What three ways may a drug be excreted?

A

By the kidneys
The gut
The lungs

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4
Q

Where are the majority of small molecules metabolised?

A

In the liver

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5
Q

If the liver is not metabolising a drug, what is?

A

Enzymes

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6
Q

What is the most common method of metabolism?

A

2-step method

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7
Q

What is the 2-step method of metabolism?

A

Phase 1: modification

Phase 2: conjugation

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8
Q

What is modification?

A

Cytochrome P450 dependent oxidase
Oxidation, reduction or hydrolysis
Creates highly reactive compounds

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9
Q

What is conjugation?

A 
Joins the metabolite onto another molecule in order to make it charged. This includes:
Glutathione
Sulfate
Glycine
Glucoronic acid
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10
Q

What are cytochrome P450 and mixed-function oxidases?

A

Important group of haem containing enzymes
Metabolise a wide range of different molecules
Important site of drug interactions
Cause oxidation, reduction or hydrolysis
Create highly-reactive compounds
May involve other enzymes

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11
Q

Give some examples of P450 interactions

A

Substrate: Amiodarone inhibits P450, it slows the metabolism of coffee
Non-substrate: Quinidine
Induction: barbiturates, Rifampicin, Phenytoin

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12
Q

What is a benefit of adding a charge to a molecule in conjugation?

A

Aids renal clearance

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13
Q

Metabolites can be active, what are the two categories of active metabolite?

A

Toxic

Therapeutic

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14
Q

Give an example of active metabolites

A

Prodrugs (convert from inactive to active)
Morphine (morphine-6-glucuronide is also an analgesic)
Pethidine (norpethidine is epileptogenic)

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15
Q

Describe the metabolism of paracetamol

A

N-hydroxylation to NAPQ1 by either CYP2E1 or CYP1A2 or CYP2D6
Conjugation to glutathione

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16
Q

What happens in paracetamol overdose?

A

Conjugation cannot occur quickly enough and NAPQ1 accumulates

17
Q

Name the routes of excretion for drugs and metabolites

A 
Renal
Hepatic/biliary
Sweat
Milk
Breath
18
Q

What actively secretes drugs into the tubules?

A

Acid transporters

Organic base transporters

19
Q

Why are ions trapped in the urine?

A

The acidic pH

20
Q

What might slow excretion of a drug in relation to transporters?

A

If two drugs are secreted by the same transporter they will be in competition

21
Q

What is the formula for Cmax?

A

C=Cmax x e^-kt

22
Q

What is the formula for the half life of a drug?

A

T1/2 = 0.6931/k

23
Q

How do you work out drug concentration if you know how many half lives have passed?

A

C=Cmax(1/2)^t/t1/2

24
Q

What is the concentration for a zero order drug?

A

C=-kt+A

25
Q

What is a zero order drug?

A

When the enzymes are saturated in its clearance

Drug Action (19 decks)

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