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ESA4 - Clinical Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is the definition of pharmacokinetics?

A

Study of movement of a drug into and out of the body

What the body does to the drug

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2
Q

What sorts of things can effect drug pharmacokinetics?

A

Renal function, liver function, GI function, CV function, disease, alcohol intake, pregnancy etc

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3
Q

What is the mnemonic for the pharmacokinetic process?

A

ADME

Absorption
Distribution
Metabolism
Elimination

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4
Q

Explain the difference between initial plasma concentrations of drugs that are given orally vs given IV

A

IV drugs - immediate peak plasma concentration

Oral drugs - takes time to be absorbed first so takes longer to reach peak plasma concentration

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5
Q

What is the therapeutic window?

A

Range of doses in which a therapeutic response is caused without adverse effects

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6
Q

What is Cmax?

A

Peak plasma concentration

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7
Q

What is Tmax?

A

Time in which peak plasma concentration (Cmax) is reached

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8
Q

What is bioavailability?

A

The fraction of a dose which enters the circulation to have an active effect

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9
Q

What is the bioavailbility for an intravenous bolus?

A

100% (all enters bloodstream)

Note that for other routes, compare amount reaching the body comartment by that route with IV bioavailability

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10
Q

On a plasma concentration/time graph, what equates to the bioavailability?

A

Area under the curve

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11
Q

How would you calculate oral bioavailability (F) from a graph?

A

F = Area under the curve (oral) / Area under the curve (IV)

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12
Q

What factors can affect bioavailability?

A

Drug formulation, age, whether its being taken with food, vomiting, malabsorption, first pass effect

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13
Q

What is first pass metabolism?

A

Metabolism that occurs before the drug enters the systemic circulation

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14
Q

Where can first pass metabolism occur?

A

Liver (via portal system)
Gut lumen
Gut wall

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15
Q

Give an example of a drug that undergoes first pass metabolism in the liver

A

Propanolol, GTN

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16
Q

Give an example of a drug that undergoes first pass metabolism in the gut

A

Benzylpenicillin, insulin

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17
Q

What two key factors influence drug distribution?

A

Protein binding and volume of distribution

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18
Q

What is the effect of protein binding on drugs?

A

They are inactive and can’t be eliminated; most drugs must be free to have a pharmacological effect

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19
Q

What factors can influence protein binding?

A

Hypoalbuminaemia (eg malnutrition), pregnancy, renal failure, displacement by other drugs

20
Q

What is the volume of distribution (Vd)?

A

A measure of how widely a drug is distributed in body tissues (proportional to half life)

21
Q

How do you calculate Vd?

A

Vd = Dose/[Drug]t0

22
Q

What is half life proportional to?

A

Volume of distribution

23
Q

What can tissue distribution be affected by?

A

Specific receptor sites in tissues, regional blood flow, lipid solubility, disease states, drug interactions

24
Q

What is a pro drug?

A

A drug that is metabolised into a pharmacologically active drug

25
Q

Give an example of an inactive pro drug

A

Enalaprilat (inactive) to enalapril (active)

26
Q

What are the main cytochrome p450 isoenzymes?

A

CYP2D6, 2C9, 2C19, 3A4

27
Q

Give an example of CYP enzyme inhibition

A

Cimetidine inhibits a CYP which slows the metabolism of warfarin

28
Q

What does CYP2D6 metabolise?

A

Codeine, beta blockers, tricyclics

29
Q

What is CYP2D6 inhibited by?

A

Fluoxetine, paroexetine, haloperidol, quinidine

30
Q

How does age affect drug metabolism?

A

Metabolism reduced in elderly and children

31
Q

What is the main route of drug elimination?

A

Through the kidney

can also be through lungs, breast milk, swear, tears, bile, saliva

32
Q

Which 3 processes determine the renal excretion of a drug?

A

Glomerular filtration, passive tubular reabsorption, active tubular secretion

33
Q

What is an example of a drug that is actively secreted in the nephron?

A

Penicillin

34
Q

How does half life relate to clearance?

A

Inversely proportional

35
Q

What effect does a reduction in clearance (or GFR) have on half life?

A

Increases half life

36
Q

What is 1st order kinetics?

A

Rate of elimination is proportional to drug level - constant fraction of drug eliminated in unit time

37
Q

What is zero order kinetics?

A

Rate of elimination is a constant

38
Q

Why do most drugs exhibit zero order kinetics at high doses?

A

Because the receptors/enzymes become saturated

39
Q

Which drugs are more likely to result in toxicity: first order or zero order?

A

Zero order - fixed rate of elimination per unit time

40
Q

What is steady state?

A

The situation where the overall intake of a drug is fairly in dynamic equilibrium with its elimination.

In practice, it is generally considered that steady state is reached when a time of 4 to 5 times the half-life for a drug after regular dosing is started.

41
Q

How many half lives are required to reach steady state?

A

4-5 half lives

  • from CpSS it also takes 4-5 half lives to eliminate most of the drug
42
Q

What is a loading dose?

A

An initial higher dose of a drug - used in acute cases, in drugs with long half life

43
Q

Give an example of a drug that usually requires a loading dose

A

Digoxin

44
Q

How do you calculate loading dose?

A

LD = Vd x target concentration of drug

45
Q

What is half life proportional to in terms of clearance?

A

t1/2 = 1/Clearance (GFR)

ESA4 - Clinical Pharmacology (20 decks)

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