Drug Metabolism Flashcards

1
Q

What is the effect of metabolism

A

limits the life of a substance in the body, by rendering lipid soluble and non-polar compounds to water soluble and polar compounds so that they can be excreted

Production of toxic metabolites (direct toxicity, carcinogenesis)

Loss of pharmalogical activity

Increase in prodrug

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2
Q

What happens to lipid soluble substances instead of getting excreted?

A

Passively reabsorbed from renal or extra renal excretory sites back into the blood

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3
Q

Purpose of metabolism?

A

To increase water solubility and so aid excretion
or to deactivate compounds (may involve a number of steps).

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4
Q

What are prodrugs?

A

Drugs activated following metabolism

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5
Q

What are phase 1 reactions of metabolism?

A

OXIDATION
REDUCTION
HYDROLYSIS

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6
Q

What is the purpose of phase 1 metabolism?

A

Increases polarity of the compound

Provides active site for phase 2 metabolism

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7
Q

What is the most important super family of metabolising enzymes?

A

P-450 enzymes

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8
Q

What is the main role of the CYP1-3 families (contained within the P-450 family)

A

Important in oxidative drug metabolism

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9
Q

Where are enzymes found that are responsible for the breakdown of SOME drugs

A

CYP3A4 - Liver + Gut

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10
Q

Why may 5-10% of the population may be immune to the analgesic actions of codeine?

A

Reduced expression of the enzyme responsible for conversion of codeine to morphine

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11
Q

Why do smokers require a higher dose of theophylline than non-smokers?

A

Enzyme responsible for the metabolism of theophylline is induced by smoking

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12
Q

What does phase 2 metabolism involve?

A

Conjugation

Attachment of glucoronic acid, glutathione, sulphate or acetate to the metabolite generated by phase 1 metabolism

Usually results in inactivation

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13
Q

What factors affect metabolism?

A

Other drugs/herbals/natural substances
Genetics
Hepatic blood flow
Liver disease
Age
Sex
Ethnicity
Pregnancy

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14
Q

What is the effect of induction of drug metabolising enzyme on metabolism?

A

Increased synthesis of the enzyme - increased activity - Decreased drug effect

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15
Q

What is the effect of inhibition of drug metabolising enzyme on metabolism?

A

Reversible or irreversible binding to the enzyme

Metabolism decreased

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16
Q

What is the effect of decreased enzyme activity or lack of an enzyme responsible for drug metabolism?

(can be as a result of genetic polymorphism)

A

Increased drug toxicity

17
Q

What are the four phenotype subpopulations of metabolizers?

A

Poor metabolizers (PM)
Intermediate metabolizers (IM)
Extensive metabolizers (EM)
Ultrarapid metabolizers (UM)

18
Q

Describe the prevalence of drug metabolising enzymes in the fetus or premature infant?

A

Deficient or reduced, renal function is also deficient so drug and metabolites rapidly build up to toxic levels.

19
Q

Who metabolises drugs faster - a teenager at puberty or an adult?

A

At puberty

20
Q

What areas in drug response does disparity occur between genders?

A

Absorption
Distribution
Metabolism
Eliminiation

21
Q

What can affect the metabolism of drugs in a pregnant woman?

A

The trimester she is in

Hormonal changes

22
Q

What factors brought about in old age alter drug metabolism?

A

Plasma protein
Lean body mass
Liver weight

DECREASE

Other drugs taken to treat chronic illness