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S2 Case 2 - Diarrhoea > Drug Metabolism + Pharmacokinetics > Flashcards

Drug Metabolism + Pharmacokinetics Flashcards

1
Q

What is a prodrug metabolised into?

A

More active form

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2
Q

What are some elimination routes?

A

Liver
Kidney
Skin
Lungs

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3
Q

What is Cmax?

A

Highest plasma con

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4
Q

What is Tmax?

A

Time at which it takes to reach Cmax

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5
Q

What is AUC?

A

Total systemic exposure to drug

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6
Q

What is vol of distribution?

A

Apparent vol in which drug is dissolved in

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7
Q

What is t1/2?

A

Time taken for plasma conc to fall by 50%

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8
Q

What is clearance?

A

The rate of drug elimination

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9
Q

When does a drug reach steady state?

A

In about 4-5 half-lives

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10
Q

What happens when it is an infusion?

A

Continuous increase until infusion stopped then decreases

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11
Q

What happens when you have increased clearance?

A

Increased dose needed

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12
Q

How do you calculate dosing rate?

A

(Target plasma con X clearance)/ Fraction absorbed

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13
Q

What is the loading dose?

A

Drug administered followed by maintenance dose

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14
Q

How do you calculate loading dose?

A

(Vol of distribution X desired steady state plasma conc)/ F

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15
Q

Describe brief route of oral drug metabolism

A

Gut —> Liver —> Site of action OR kidney

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16
Q

What are the drug metabolising enzymes found in liver?

A

Cytochrome 540s
Alcohol dehydrogenase
Esterases

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17
Q

What is 1st pass effect?

A

Drugs extracted so efficiently by liver only small amount reaches systemic system

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18
Q

What are some examples of drugs that undergo substantial 1st pass?

A

Aspirin
Levodopa
Propranolol

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19
Q

What are the 2 processes of metabolism?

A

Phase I
Phase II

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20
Q

What happens in Phase I?

A

Made into more polar
OXIDATION

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21
Q

What happens in Phase II?

A

Conjugation

22
Q

What is an outcome of Phase I?
1

A

More pharmacologically active after metabolism
eg. Enalaprilat poorly absorbed so rely on metabolism to convert

23
Q

What is an outcome of Phase I?
2

A

Alter pharmacological action of drug
eg. aspirin inhibits platelet function + NSAID
BUT hydrolysed to salicylic acid = NSAID

24
Q

What is an outcome of Phase I?
3

A

Metabolites have similar actions to parent compound
eg. benzodiazepines form active metabolites that cause sedation

25
Q

What is an outcome of Phase I?
4

A

Metabolites responsible for toxicity

26
Q

What is the 1 of the most important cytochrome P450s in metabolism?

A

CYP34A

27
Q

What can CYP450 genetic variability cause?

A

Gain of function effect
OR
Loss of function effect

28
Q

What can some drugs do to CYP450s?

A

Induce them
= increase biotransformation of drugs
= decreases plasma conc

29
Q

What are examples of drugs that are CYP inducers?

A

Phenobarbital
Rifampin

30
Q

What can inhibition of CYP lead to?

A

Significant increase in plasma drug conc + potential drug toxicity

31
Q

What is an example of CYP inhibitor?

A

Omeprazole = CYP2C19
Involved in clopidogrel metabolism
When taken with omeprazole, clopidogrel (inactive) plasma conc increases
= decreases anti-platelet effect

32
Q

What happens in Phase II?

A

X

33
Q

What is the most common Phase II?

A

Catalysis by UDP (UGT)

34
Q

What are UGTs?

A

Superfamily of enzymes that catalyse conjugation f glucuronic acid to facilitate systemic elimination

35
Q

What happens with elderly?

A

Changes in all PK areas
= metabolism + excretion decrease
= 1st-pass decreases
= hepatic metabolism by CYP450s decrease

36
Q

Why can toxicity in elderly patients develop slowly?

A

Concs of chronically used drugs increase to 5-6 half-lives

37
Q

What does research show about age?

A

Does NOT affect clearance of drugs that are metabolised by conjugation (Phase II)

38
Q

What does inflammatory disease of liver effect?

A

Function of hepatocytes + blood flow
= reduce drug extraction
= increased systemic availability

39
Q

What is the effect of pregnancy on metabolism?

A

Hormone levels raised
= regulate expression of metabolising enzymes

40
Q

What is BBB?

A

Selectively permeable membrane
= between blood stream + extracellular space of brain

41
Q

What is function of BBB?

A

Regulate passage of molecules

42
Q

What does the BBB contain?

A

Endothelial cells lining capillaries
Tight junctions that lack intra-cellular pores
Glial tissues cover capillaries

43
Q

What does BBB allow?

A

High lipophilic drugs to diffuse passively

44
Q

How does moderately lipid soluble of partially ionised molecules penetrate BBB?

A

At slow rate

45
Q

How does glucose cross BBB?

A

Glucose transporter 1 (GLUT1)

46
Q

What is Parkinson disease (PD)?

A

Degeneration of dopaminergic neurons

47
Q

Can dopamine cross BBB?

A

NO

48
Q

What is used to treat PD BUT what is problem?

A

Levodopa
BUT extensively decarboxylated to dopamine in peripheral tissues

49
Q

So how is levodopa given?

A

Given in combination with DOPA decarboxylase inhibitor that does NOT cross BBB

50
Q

What are the approaches to cross BBB?

A

Enhance lipid solubility
Use of transporters/carriers
Inhibition of efflux transporters
Prodrug bioconversion

S2 Case 2 - Diarrhoea (12 decks)

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