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Human Diseases > 4.1 Principles of pharmacology > Flashcards

4.1 Principles of pharmacology Flashcards

1
Q

What is pharmacokinetic variability?

A

The variability of a drug between the dose and the serum drug concentration.
The change in plasma concentration of the drug over time.
Effectively what the body does to the drug.

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2
Q

What is pharmacodynamic variability?

A

The relationship between drug dose and response.
Effectively what the drug does to the body.

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3
Q

What is PK and PD?

A

PK = pharmacokinetics
PD = phramacodynamics

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4
Q

What does [drug]se mean?

A

Square brackets = concentration
se = plasma
Dot above drug refers to how drug concentration changes in body with time.

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5
Q

What factors influence pharmacokinetic variability?

A
  • Age
  • Disease (e.g. affecting liver, kindeys, CV system)
  • Genetics
  • Other xenobiotics (chemical substances affecting the body)
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6
Q

What factors influence pharmacodynamic variability?

A
  • Age
  • Disease
  • Genetics
  • Other xenobiotics
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7
Q

What is the host response divided into?

A
  • Beneficial
  • Harmful
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8
Q

What is meant by the term therapeutics?

A

Process of optimising beneficial effects of a drug whilst minimising harmful effects.

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9
Q

Why is pharmacokinetics important?

A
  • Determines the drug concentration at the site of action (including on target and off target effects)
  • Determines dose and dose-interval selection (time between doses)
  • Determines if dose adjustment or dose-interval adjustment is needed (e.g. extremes of age, liver/kidney impairment, other xenobiotics)
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10
Q

Pharmacokinetics is the net effect of which 4 simultaneous reaction types?

A

ADME
- Absoprtion
- Distribution
- Metabolism
- Elimination

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11
Q

Drugs normally follow which 2 types of kinetics?

A
  • Zero order kinetics
  • First order kinetics
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12
Q

What is meant by the term zero order kinetics?

A
  • Where the amount of a drug changes at a constant rate.
  • Rate of reaction is independent of drug concentration.
  • Linear relationship between rate of change of drug concentration and time (straight diagonal line).
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13
Q

What is meant by the term first order kinetics?

A
  • Most drugs follow first order kinetics.
  • Amount of drug changes at a rate that is proportional to the amount of drug in the body.
  • The change in drug concentration over time is dependent on the initial drug concentration, heavy involvement of physiological mechanisms.
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14
Q

What is meant by the term “velocity of reaction”?

A

The velocity of the reaction = rate of reaction

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15
Q

Give examples of drugs that exhibit zero order kinetics.

A
  • Alcohol
  • Aspirin
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16
Q

What is a non-linear pharamacokinetic model?

A

Non-linear relationship between dose and plasma concentration.
The drug has a narrow therapeutic index.
Small dosage increases in some patients may produce large rises in plasam concentrations with acute toxic side effects.
Narrow margin between therapeutic dose and toxicity.
E.g. phenytoin

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17
Q

Define absorption in pharamcokinetics.

A

The passage of a drug from the site of administration to the plasma e.g. orally.

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18
Q

What are the 2 key parameters in absorption?

A

Cmax and Tmax

19
Q

What is Cmax?

A

Maximum concentration of the drug in plasma.
Depends on dose and bioavailability.
Affected by ability to cross anatomical barriers and metabolism.

20
Q

What is Tmax?

A

The time of Cmax.
Affected by guy motility and splanchnic blood flow.

21
Q

What does AUC stand for?

A

Area under the curve.

22
Q

How can drugs cross anatomical barriers?

A
  • Diffusion through lipids
  • Using transporter molecules
  • Through aquaporin channels
  • Pinocytosis
23
Q

Which key factors influence the extent to which drugs can diffuse through lipids?

A
  • Size of molecules
  • Charge

pH of environment affects molecular polarity

24
Q

Define distribution in pharmacokinetics.

A

The extent to which a drug can enter a different anatomical compartment.

25
Q

What is volume of distribution (Vd)?

A

Relates the total amount of drug in the body to plasma concentration. Therefore determines loading dose.

26
Q

What is loading dose?

A

The appropriate drug concentration when it is first administered.

27
Q

Which 3 factors affect volume of distribution?

A
  • Lipid/water solubility
  • Plasma protein binding
  • Carrier mediated transport (organic anion/cation transporters and P-glycoprotein transporters)
28
Q

What does Cp mean?

A

Plasma concentration.

29
Q

What is the main site of drug metabolism?

A

The liver

30
Q

Describe phase 1 metabolism.

A

Carabolic reactions which introduce active functional groups to the molecule, making it more reactive in preparation for phase 2.

31
Q

Describe phase 2 metabolism.

A

Conjugation of larger, water-soluble molecules to the functional group, this reduces the volume of distribution of the drug and increases renal clearance.

32
Q

What is the risk of bioactivation?

A

Risk of bioactivation: a relatively non-toxic drug can undergo phase 1 reactions and become toxic e.g. paracetamol.

33
Q

What is elimination in pharmacokinetics?

A

Loss of the drug from the body.

34
Q

What does Cl mean?

A

Clearance (Cl): determines relationship between dose rate and steady rate concentration.

35
Q

What are the 4 routes of drug elimination?

A
  • Renal (ultrafiltration, tubular secretion or passive diffusion)
  • Enterohepatic circulation (drug secreted into bile, released into intestines)
  • Exhalation
  • Sweat and stool (minor)
36
Q

What is half life?

A

Half life (t 1/2): time taken for the concentration of drug to fall by half.

37
Q

How many half-lives does it take to reach the steady state of a drug for drugs that undergo first order kinetics?

A

5 half-lives to reach steady state

38
Q

What happens to the peak:trough ratio as dose increases, and as dose-interval decreases?

A

Dose increase = peak:trough increase
Dose-interval decrease = peak:trough decrease

39
Q

Name the key structures that drugs act on.

A
  • Receptors
  • Ion channels, transporters and pumps
  • Enzymes
  • Genome
  • Direct chemical and physical reactions
40
Q

What are the 2 ways of studying the interaction between a drug and its receptors?

A
  • Studying affinity between drug and molecular target: use affinity constant. Produces Scatchard plot.
  • Studying drug-receptor efficacy: to see if drug is actually having any effect on its target. Uses inhibitory constant (IC50) or excitatory constant (EC50).
41
Q

What are the 4 types of drug when looking at drug concentration and effect in pharmacodynamics?

A
  • Full agonist
  • Partial agonist
  • Antagonist
  • Inverse agonist (eliminate normal cell function and reverse cell development)
42
Q

Summarise the key 3 points regarding pharmacokinetics.

A
  • Determines drug concentration at site of action
  • Determines dose and dose interval selection
  • May need to adjust dose and dose-interval in certain cases
43
Q

Summarise the key 3 points regarding pharmacodynamics.

A
  • Determines type of response
  • Determines potency
  • Determines specificity

Human Diseases (47 decks)

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