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Pharmacology for FRCR CO1 > 2.3 Pharmacokinetics and pharmacodynamics > Flashcards

2.3 Pharmacokinetics and pharmacodynamics Flashcards

1
Q

What is pharmacodynamics?

A

What the drug does to the body
- Therapuetic activity
- Toxicity due to ‘on target’ or ‘off target’ effetcs

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2
Q

What is the Therapuetic Index?

A

Dose required for a toxic effect LD50
divided by dose required for effective therapeutic effect ED50

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3
Q

What is Pharmacokinetics?

A

What the body does to the drug

ADME

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4
Q

What is ADME of Pharmacokinetics?

A
  • Absorption
  • Distribution
  • Metabolism
  • Excretion
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5
Q

What is Absorption of a drug? What type of drug administration does Absorption not apply?

A

Process by which drug is transferred from site of administration to site of measurement e.g. into the blood stream

This does not apply to IV drugs

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6
Q

What does Absorption of a drug depend on?

A
  • Passive diffusion
  • Active transport
  • Endocytosis
  • Route of administration e.g. pO, IM, SC
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7
Q

What is Distribution of a drug?

A

Reversible Transfer of drug to and from site of measurement (e.g. blood)

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8
Q

What factors affect drug distribution?

A
  • Blood flow
  • Capillary permeability
  • Tissue binding
  • Regional pH level
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9
Q

How does tissue binding

A
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10
Q

How does blood flow affect drug Distribution?

A

Distribution occurs more rapidly in tissues with high blood flow e.g. lungs kidneys, liver, brain
and more slowly in poorly perfused e.g. fat and peripheral muscle

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11
Q

How does capillary permeability affect drug distribution?

A

distribution slower in tissues with tight junctions between endothelial cells forming capillaries e.g. brain, and quicker in tissues with porous capillaries (e.g. liver and kidney)

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12
Q

What is plasma protein binding?

A

Attachment of drugs to proteins in the blood (albumin and a-1 acif glycoprotein)

Drugs can be bound or unbound
A bound drug has no effect in the body and doesn’t easily get into cell

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13
Q

What does the amount of bound drug depend on?

A
  • concentration of the free durg
  • concentration of the protein
  • affinitiy of drug to binding sites
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14
Q

What charcateristic must a drug have to be able to cross biological barriers such as brain or placenta?

A

Highly soluble

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15
Q

What are some highly bound chemotherapies?

A

Paclitaxel
Etoposide

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16
Q

What is a drug that does not bind to plasma proteins?

A

Cisplatin

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17
Q

What is the Volume of Distribution (Vd)? What do high and low Vd signify?

A

Theoretical volume that represents the degree to which the drug is distributed in tissue

High Vd = More in tissue less in plasma
Low Vd = More in plasma less in tissue

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18
Q

How is the Volume of Distribution (Vd) calculated?

A

Vd = total amount of drug in body/ drug blood plasma concentration

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19
Q

What factors contribute to a high Vd?

A
  • Lipid soluble
  • Low plasma protein binding
  • Low rates of ionisation
  • Highly tissue bound
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20
Q

How does lipid diffusion transport drugs?

A

Passive (no energy or carriers) movement of drugs across cell membranes due to the concentration gradient

As membranes are lipid bilayers drugs have to be lipophilic (fat soluble) and non-ionised to diffuse across a membrane

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21
Q

What factors determine a drug’s lipid solubility?

A
  1. Lipid:water partition coefficient (LogP). a High LogP = more lipophilic, crosses BBB
  2. Ionisation - non-ionised more soluble
  3. pKa of drug
  4. pH of fluid - substance will be more lipid soluble (less ionised) in a solution with similar pH to its own
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22
Q

What is pKa?

A

pKa is the pH at which the concentration of ionised and non-ionised form of drug is equal

low pKa = stronger acid

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23
Q

What is Metabolism?

A

Elimination of a drug by chemical modification

This can be sponatneous or due to enzymes

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24
Q

What are the two types of metabolic product?

A
  • More toxic/active product - bioreductive, prodrug acrivarion
  • Less toxic/active than parent drug (detoxification)
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25
Q

How are drugs metabolised in the liver? (2 phases)

A

Phase I - enzymes (usually P450) modify the drug through oxidation, reduction, hydrolysis

Phase II - conjugation of drug or oxidised metabolite to carbs, proteins or sulfur to make them more water soluble so they can be secreted in bile or urine

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26
Q

What types of drug conjugation can occur in phase II metabolism?

A
  • Glucoronidation
  • Glutathione conjugation
  • Acetylation
  • Methylation
  • Sulfation
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27
Q

What is First Pass Metabolism?

A

Oral drugs enter the liver or gut and are metabolised by enzymes before entering the systemic circulation - reducing bioavailability

This can inactive drugs or activate pro drugs (e.g. codeine -> morphine)

Drugs that undergo first pass metabolism need higher doses or alternative routes

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28
Q

What determines p450 activity?

A
  1. Genetics
  2. Polymorphisms or single nucelotidr polymorphisms (activity or expression)

High P450 lowers drug plasma levels - reducing drug action

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29
Q

What is Excretion?

A

Removal of drug from the body, either as a metabolite or unchanged

30
Q

What are the major routes of drug excretion?

A
  • Urine
  • Bile
31
Q

What are the minor routes?

A
  • Sweat
  • Tears
  • Reproductive fluid
  • milk
  • Faeces
32
Q

What is clearence/elimination?

A

Organ’s ability to clear drug from bloodstream

33
Q

What external factors affect drug clearance?

A
  1. Smoking - induces CYP1A1 and 1A2
  2. Alcohol - induces CYP2E1
  3. Grapefruit juice - inhibits CYP3A2
  4. Cabbage vegetables - induces CYP1A2
  5. Calcium in diet can chelate drugs
34
Q

What patient factors can affect drug clearance?

A

Very young - immature kidneys and liver

Elderly

35
Q

What is Zero Order elimination kinetics? Does it depend on drug concentration?

A

Constant amout of drug is eliminated per unit of time

Independent of drug cocnentration

36
Q

What are some examples of zero order eliminated drugs?

A
  • Alcohol
  • Phenytoin
  • Salicylates
  • Theophylline
37
Q

What is the formula for Zero-order elimination?

A

change in drug concentration / change in time = -k*

dC/dt or dA/dt

38
Q

What is frist order elimination kinetics? Does it depend on drug concentration?

A

A constant proportion (e.g. percentage) of drug is eliminated per unit of time

ADME follows this - most drugs

e.g. 10% per hour

Dependent on drug concentration

39
Q

What is the Half-life of a drug? (T1/2)

A

The time for concentration of a drug in the blood to fall by 1/2 irs orginal value

40
Q

What is the equation for half-life?

A

0.693/Ke
Where Ke is the elimination constant

41
Q

What is a drug steady state?

A

Where rate of administration is equal to rate of elimination

42
Q

How many half lifes does it take to attain steady state?

A

4 or 5

The time to steady state is independent of dose

43
Q

What parameters can be determined from a concentration vs time curve?

A

Cmax - Max concentration in plasma
Tmax - time when maximum concentration in plasma
AUC - area under the curve

44
Q

What is the bioavailability (F) of a drug?

A

Compares the amount of drug reaching systemic circulation following non IV administration vs. amount of drug following IV adminsitration

45
Q

What is the equation for Bioavailability?

A
46
Q

What is the loading dose?

A

The initial dose needed to reach a certain plasam concentration

47
Q

What is the equation for loading dose?

A

peak drug concentration (Cp) x Vd
divided by Bioavailability

48
Q

What is the maintainence dose?

A

Dose needed to reach steady state (in = out)

49
Q

What is the equation for maintainence dose?

A
50
Q

What are the shapes of the pharmacokinetic profiles of different drug administration routes?

A

No absorption phase for IV

51
Q

What is the shape of the graph of a single IV bolus injection?

A
52
Q

What is the shape of the graph for an IV infusion?

A
53
Q

What is the therapeutic range?

A

Range between
MEC = Minimum Effective Concentration
MTC = Minimum Toxic Concentration

This is narrow in oncology

54
Q

What are the 3 types of pharmacokinetic drug resistance?

A
  1. Inherent - cells can’t respond
  2. Acquired - tumour cells initially sensitive but become insensitive
  3. Apparent resistance - cells are sensitive but delivery is inadequate or incorrect
55
Q

What is the Area Under the Curve?

A

Represents total exposure over time

AUC = concentration of a drug in the body that the oncologist wants to achieve

Drug concentration vs time (mg/ml/min)

= Bioavailability x Dose/Clearance

56
Q

What is AUC dependent on?

A
  1. Rate of elimination - gradient of curve
  2. Dose - starting point on Y axis
57
Q

What is Calvert’s formula?

A

Dose (mg) = Target AUC (mg/ml/min) x (EGFR (ml/min) + 25 ml/min)

58
Q

What are the different doses for target AUC at 125ml/min CrCl?

A

AUC 6 = 6x150 = 900mg
AUC 5 = 5 x150 = 750mg
AUC 4 4X150 = 600mg

59
Q

How is eGFR calculated?

A

(140-age) x weight x constant/creatinine

constant men 1.23
women 1.04

60
Q

How is Adjusted Body Weight calculated?

A

IBW + 0.4 (TBW - IBW)

61
Q

How does renal impairment affect ADME?

A

A - uraemia, gut oedema
D - oedema, protein binding
M - phase 1 reaction slow
E - impaired renal excretion

62
Q

What drugs have 90% renal excretion?

A
  1. Carboplatin
  2. Cisplatin
  3. Methotrexate
63
Q

How does impaired liver function affect ADME?

A

A - cholestatis, portal systemic shunting

D - acites, protein binding, bilirubin can displace highly bound drugs

M - phase I and phase II

E - hepatic blood flow, cell mass, cholestasis

64
Q

What is the importance of drug concentration at the target site?

A

Determines therapeutic effect and safety

65
Q

What is a full agonist?

A

Drug that produces max response after binding to receptor

66
Q

What is a partial agonist?

A

Produces sub-max response after binding to receptor

67
Q

What is a competative antagonist?

A

Competitive - binds to the same site as a ligand, reversed by increasing ligand concentration

68
Q

What is a non-competative antagonist?

A

binds at alternative allosteric site, not overcome by increasing ligands

69
Q

What is an irreversible antagonist?

A

Binds to active site/alternative site irreversibly

70
Q
A

Pharmacology for FRCR CO1 (7 decks)

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