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BU Toxicology 3, 6, 9, 12, 15, 18 > Metabolism (L3) > Flashcards

Metabolism (L3) Flashcards

1
Q

What is the primary site of metabolism?

A

The Liver

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2
Q

What compounds can be metabolised in the liver?

A

Endogenous/Exogenous

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3
Q

Name other organ sites that are active in metabolism

A

Lung
Kidney
Intestine
Placenta
Adrenal
Skin

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4
Q

Metabolism may result in…

A

Active drug -> inactive metabolite
Inactive drug -> active drug
Active drug -> active metabolite

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5
Q

Name a drug example that gains activity after being metabolised.

A

Pro-drugs
L-Dopa -> Dopamine (parkinson treatment)
Clofibrate -> Clofibric acid (lowers cholesterol)
Lovastatin -> Lovastatin acid (treats hypertension)

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6
Q

Name a drug example that gains activity after biotransformation (known as pro-drugs)

A

L-DOPA -> Dopamine (parkinson treatment)
Clofibrate -> Clofibrate acid (lowers cholesterol)
Lovastatin -> Lovastatin acid (treats hypertension)
Cortisone -> Hydrocortisone (calms down immune response)

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7
Q

Name a drug example that transforms to a more active compounds after biotransformation

A

Codeine -> Morphine (opiod pain relief)
Imipramine -> Desmethylimipramine (anti-depressant)

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8
Q

Name a drug example that is less active compound after biotransformation

A

Aspirin -> Salicyclic acid (pain relief)
Meperidine -> Normeperidine (moderate to severe pain relief)
Lidocaine -> De-ethyl lidocaine (anaesthetic)

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9
Q

What is first pass effect?

A

Drugs that are taken orally pass though liver where the drug is removed by metabolism or hepatobiliary secretion

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10
Q

What is Phase I metabolism

A

Reactions which introduce or unmask hydrophilic groups in the drug structure (functionalisations)

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11
Q

What is Phase II metabolism

A

Reactions which conjugate the drug or its phase-I metabolite with a hydrophilic, endogenous species (conjugation reactions)

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12
Q

Describe what occurs in Phase I metabolism

A

Metabolises drugs to create sites for Phase II metabolism
1) Oxidation via microsomal endoplasmic reticulum cytochrome P450 liver enzymes
2) Reduction mediated by P450 enzymes
3) Hydrolysis performed by hydrolytic enzymes called plasma esterases

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13
Q

What enzymes are a part of Phase I metabolism

A
  • Cytochrome P450 liver enzymes
  • Kidney and nervous tissue enzymes
  • Plasma esterases
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14
Q

What enzymes perform oxidation reactions?

A

Liver enzymes (hepatocytes) which are localised in the endoplasmic reticulum (ER) in microsomal fractions
- cytochrome P450 mined-functional oxidases

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15
Q

What is needed for an oxidation reaction to occur?

A

Molecular Oxygen (O2) and NADPH

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16
Q

What is the active site of the Cytochrome P450?

A

Cytochrome P450 is a “hem” containing protein where the active site is the Fe

  • Can only bind drug if the Fe is oxidised to Fe3+
  • Forms enzyme-drug complex where electron is released from NADPH
  • Reducted EDC binds to molecular O2
  • Enzyme-drug-O2 complex breaks down into oxidised enzyme, water and oxidised drug
17
Q

What enzyme reduces NADPH

A

NADPH-cytochrome P450 reductase

18
Q

What is glucoronidation

A

Most common reaction that takes place in the liver.
Glucaroninc acid combines with -OH, -SH, -COOH and -COHN groups to create glucuronide mtabolites

19
Q

What reactions take place in Phase II metabolism?

A

Conjugation reactions

20
Q

Which enzymes catalyse glucuronidation?

A

UDP-glucuronoslytransferases (UGTs)
- Located in endoplasmic reticulum of liver cell
- Only conjugation reaction performed by microsomal enzymes

21
Q

Name a drug example that are conjugated with glucuronic acid?

A
  • Chloramphenicol
  • Salicyclic acid
  • Morphine
  • Endogenous compounds (steroids and bilirubin)
22
Q

Variable metabolism occurs as a result of…?

A
  • Age
    -Gender
  • Disease states
  • Drug tolerance
  • Species
  • inducers/inhibitors
23
Q

What can change enzyme efficacy?

A

Polymorphism
- Mostly in the CYP family may have the most impact

24
Q

Iduction of microsomal enzymes leads to…

A

Increases amount/activity of P450 enzymes = decreased drug effect

25
Q

Inhibition of microsomal enzymes

A

Decreases amount/activity

BU Toxicology 3, 6, 9, 12, 15, 18 (5 decks)

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