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Basic Pharmacology > Metabolism and Excretion > Flashcards

Metabolism and Excretion Flashcards

1
Q

Enterohepatic recirculation

A

Drugs that are eliminated in bile can be reabsorbed in GI tract

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2
Q

2 processes forming elimination?

A

Metabolism + excretion

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3
Q

Where does elimination mainly occur?

A

Kidney, liver, hepato-bilary system

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4
Q

Main purpose of metabolism?

A

make lipid soluble drugs more water soluble

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5
Q

Metabolism?

A

Enzymatic modification of a drug

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6
Q

Where does meatbolism occur?

A

Liver

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7
Q

Purpose of phase 1 metabolism?

A

Activate pro-drugs (introduce functional group)

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8
Q

What enzyme regulates phase 1 metabolism?

A

Cytochrome P450

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9
Q

Most common phase 1 metabolism?

A

Oxidation reaction

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10
Q

Result of phase 1 metabolism?

A

Decreased lipid solubility

Increase pharmacological activity (activate pro-drugs)

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11
Q

Where in liver/intestine is cytochrome P450 formed?

A

In ER or hepatocytes/enterocytes

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12
Q

What type of reaction is phase II metabolism?

A

Conjugation reaction

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13
Q

What part of the molecule does phase II metabolism target?

A

Functional group

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14
Q

End product of conjugation?

A

Further decreased lipid solubility and pharmacologically inactive molecule

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15
Q

Conjugation reaction?

A

Addition of group (acetyl, glucoronide) to decrease lipid solubility

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16
Q

Most common conjugate reaction phase II reaction?

A

Glucuronidation

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17
Q

Why are glucuronides inactive ad rapidly secreted?

A

Highly polar

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18
Q

What enzyme is used in glucoronidation?

A

UDP-glucoronyl transferase

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19
Q

How is paracetamol metabolised at therapeutic doses?

A

Mostly by phase II reaction by glucuronic acid
In liver
Minor proportion by cytochrome P450 = but this forms a toxic metabolite which is detoxified by phase II

20
Q

How is paracetamol metabolised at overdose?

A

Phase II reaction substrates are saturated so more is metabolised by cytochrome P450 = more toxic metabolite
These react with liver proteins = tissue damage and hepatic necrosis

21
Q

3 phases of renal excretion?

A

Glomerular filtration
Tubular secretion
Tubular reabsorption

22
Q

How much fo drug is filtered at glomerulus?

A

20%

23
Q

Rate of glomerular function dependent on?

A

Concentration of free drug in plasma and molecular weight

24
Q

Why is albumin not filtered at glomerulus?

A

Molecular weight too high

25
Q

Is glomerular filtration affected by lipid solubility or pH?

A

No

26
Q

Where does active tubular secretion occur?

A

Proximal tubule

27
Q

How is drug transferred into the lumen of proximal tubule?

A 
Acids = acidic carrier against electrochemical gradient
Bases = Organic carrier
28
Q

Is PPB a barrier to carrier mediated transport?

A

No

29
Q

How can competition occur in tubular secretion?

A

If drugs use same transporter

30
Q

Where does tubular reabsorption occur?

A

Loop of Henle

31
Q

As more water is reabsorbed how does drug concentration change?

A

Decreases

32
Q

What is tubular reabsorption dependent on?

A

pKa lipid solubility

pH of tubular fluid

33
Q

If tubule fluid is alkaline how will this affect reabsorption of acid and basic drugs?

A 
Acids = ionised = won't pass through membrane = high urine concentration
Bases = union ionised = pass through = less concentrated in urine
34
Q

Impact of urinary acidification of excretion?

A

Acidic drugs = unionised so reabsorbed

Basic drugs = ionised = high concentration = more excretion

35
Q

How do mechanisms of elimination depend on physicochemical properties?

a) lipid soluble
b) water soluble
c) volatile gases

A

a) metabolised to water soluble and excreted into urine
b) unchanged in urine
c) exhalation

36
Q

Saturable elimination?

A

Above therapeutic dose the elimination mechanisms are saturated so not eliminated well

37
Q

Clearance?

A

Volume of plasma cleared of compound per unit of time

38
Q

How is clearance of IV calculated?

A

IV dose/AUC

39
Q

How is clearance of oral dose calculated?

A

Oral dose X F/oral AUC

40
Q

How can clearance be calculated without graph?

A

Ke x Vd

41
Q

Ke

A

Elimination rate constant = slope of log concentration time

42
Q

How is half life calculated?

A

0.693/Ke

43
Q

Purpose of inducers?

A

Increase synthesis of phase I and II enzymes to increase metabolism

44
Q

Implications of inducers?

A

Decrease drug effectiveness on chronic exposure
Need higher dose
Problem when withdrawn

45
Q

How can alcohol consumption effect paracetamol metabolism?

A

Ethanol = induces cytochrome P450 = more metabolised by CYP450 = more toxic metabolite

Basic Pharmacology (12 decks)

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