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Pharmacology > Drug Elimination I > Flashcards

Drug Elimination I Flashcards

1
Q

Other than plasma, what compartments can drugs distribute to

A

Interstitial fluid

Fat store

Intracellular fluid

Trans cellular fluid

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2
Q

Why isn’t drug distribution equal

A

Blood perfusion to organs /tissues

Ability to cross membranes (lipid solubility,ionisation)

Plasma protein binding (if bound can’t pass)

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3
Q

What is another barrier apart from the GI tract

A

Blood brain barrier

Drugs can’t enter the brain from blood unless psychotic

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4
Q

What does albumin bind to

A

Acidic drugs

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5
Q

Which protein can bind to neutral drugs

A

a1 acid glycoprotein

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6
Q

What happens if drugs are bound to eg A1 acid glycoproteins

A

They can’t pass membranes into other fluid compartments

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7
Q

How do you work out volume of distribution of drug (Vd)

A

Total amount of drug administered (Q)
/
Plasma concentration of drug (Cp)

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8
Q

Why does chloroquine drug have high volume of distribution

A

Because it’s lipiphillic

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9
Q

Why do drugs like heparin and warfarin have a low Vd

A

Because they are bound to proteins so more in the plasma

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10
Q

Which types of drugs need to be metabolised first before elimination and why

A

Lipophillic drugs

Need to be converted to water soluble products before elimination eg via kidney

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11
Q

What are the major sites of metabolism

A

Liver , enterocytes , kidney, lungs

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12
Q

What kind of reactions are phase 1

A

Catabolic

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13
Q

What are drugs introduced to in phase 1 to become reactive/ soluble

A

OH, amino NH2, COOH(carboxylic)

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14
Q

What are the 3 oxidation reactions which occur in phase 1 (loss of e/h)

A

1- hydroxylation : H —-> OH

2- deamination: NH2 —-> C=O

3- dehydrogenation: OH ——> C=O

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15
Q

Where do oxidation reactions occur and name some enzymes

A

Liver
(Monooxygenases)
Cytochrome p450
Alcohol dehydrogenase

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16
Q

Which kind of reaction occurs in reduction (gain of H/e)

A

Hydrogenation

C=O —-> OH

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17
Q

Which enzymes are involved in reduction in phase 1 (hydrogenation)

A

Reductases

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18
Q

What is the 3rd reaction type in phase 1 and where does it occur

A

Hydrolysis (addition of HOH)

Usually in plasma (not often in liver)

19
Q

What are the enzymes involved in hydrolysis usually in plasma

A

Esterases eg cholinesterase, peptidase

20
Q

What do cytochrome p450s require in oxidation

A

Oxygen, NADPH, NADPH reductase

21
Q

Why do P450 vary

A

Species differences
Environmental factors which can induce them
Genetic polymorphism
Other drug interference

22
Q

What does aspirin esterase do

A

Hydrolyses aspirin into salicylate

23
Q

WhAt does butrylcholine esterase do

A

Hydrolyses SUXAMETHONIUM drug which usually binds to cholinergic receptors and causes muscle paralysis

24
Q

Where do phase 2 reactions occur

A

Usually in liver but can happen in kidney or lung too

25
Q

What happens in phase 2

A

Donors add a group to the drugs to make them less reactive than in phase 1 = form a conjugate

26
Q

Give an example of a donor in phase 2

A

Acetyl coA which forms an acetyl conjugate out of the drug

27
Q

What are prodrugs

A

Drugs which become active only within metabolism

28
Q

Give 3 examples of drugs which become active after metabolism (prodrugs)

A

Diacetylmorphine—-> morphine

L dopa —-> dopamine

Valaciclovir —-> acyclovir

29
Q

Where are most drugs which aren’t absorbed excreted

A

In the gut as faeces

30
Q

Which kind of drugs are excreted through the kidney as tribe

A

Water soluble via metabolism

31
Q

Give 3 other excretion sites other than gut and kidney

A

Liver in bile which is emptied to small intestine

Gases —> exhaled

Secretion in glands —> breast milk or sweat

32
Q

When can saturation of elimination route happen and what happens in result

A

If organ is failed eg kidney failure

Causes build up in plasma which is toxic

33
Q

What is CLtot

A

Total clearance

Volume of plasma which has been cleared of the drug per unit of time

34
Q

How do you work out total clearance cltot

A

Dose / total exposure (AUC)

35
Q

How do you work out clTOT for administration with little bioavailability

A

Dose x bioavailability/ AUC (exposure)

36
Q

What is first order kinetics in elimination

A

Rate of elimination is related to Cp (plasma conc)

How much of the drug given affects Kel

37
Q

What is Kel

A

Elimination constant rate

38
Q

How do you work out Kel

A

CLtot/ volume of distribution

39
Q

How do you work out Kel from a slope on a graph

A

Plot conc and time and then take 2 readings under curve

Do log concA/conc B

/ time difference between A and B

40
Q

What is elimination half life

A

Time taken for plasma drug conc Cp to decrease by 1/2

41
Q

How do you work out half life elimination off the same slope a and b

A

Log2
/
Kel

42
Q

How many half life’s do drugs have

A

6

43
Q

When can someone’s half life increase

A

If they have lower conc of enzymes in metabolism eg via age,genetics or taken inhibitors for eg CYP enzymes

Means they have lower rates of metabolism and elimination

44
Q

What is zero order kinetics

A

Dosage of the drug given isn’t related to plasma conc and Kel

Elimination is limited due to other factors such as number of enzymes rather than dosage/conc of drug

Pharmacology (24 decks)

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