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(LUSUMA) Clinical Pharmacology & Therapeutics > S2) Pharmacokinetics > Flashcards

S2) Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

Pharmacokinetics is the study of the movement of a drug into and out of the body

“What the body does to the drug”

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2
Q

What is pharmacodynamics?

A

Pharmacodynamics is the study of drug effect and mechanisms of action

“What the drug does to the body”

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3
Q

What is pharmacogenetics?

A

Pharmacogenetics is the effect of genetic variability on the pharmaco- kinetics/dynamics of a drug on an individual

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4
Q

What are the two forms of drug administration?

A
  • Enteral – delivery into internal environment of body (GI tract)
  • Paraenteral – delivery via all other routes that are not the GI
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5
Q

What are the 9 different types of drug administration into the body?

A
  • Oral
  • Intravenous
  • Intramuscular
  • Transdermal
  • Inhalation
  • Subcutaneous
  • Sublingual
  • Intrathecal
  • Rectal
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6
Q

Briefly, identify and describe the four main processes involved in drug therapy?

A
  • Pharmaceutical process – “Is the drug getting into the patient?”
  • Pharmacokinetic process – “Is the drug getting to its site of action?”
  • Pharamcodynamic process – “Is the drug producing its required pharmacological effect?”
  • Therapeutic process – “Is the pharmacological effect being translated into a therapeutic effect?”
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7
Q

What are the four processes involved in pharmacokinetics?

A
  • Drug in:

I. Absorption

II. Distribution

  • Drug out:

I. Metabolism

II. Excretion

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8
Q

What is bioavailability?

A

Bioavailability is the fraction of a dose which finds its way into a body compartment (usually the circulation)

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9
Q

How does one calculate oral bioavailability?

A

Oral Bioavailability (F) = AUCoral / AUCIV

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10
Q

What are the factors which affect bioavailability?

A
  • Absorption – drug formulation, age, food, vomiting / malabsorption
  • First pass metabolism
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11
Q

What is first pass metabolism?

A

First pass metabolism is any metabolism occurring before the drug enters the systemic circulation

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12
Q

Identify three common locations where first pass metabolism occurs

A
  • The Gut Lumen
  • The Gut Wall
  • The Liver
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13
Q

What is drug distribution?

A

The distribution of a drug refers to its ability to ‘dissolve’ in the body

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14
Q

What are the two factors affecting drug distribution?

A
  • Protein binding
  • Volume of Distribution (Vd)
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15
Q

In three steps, explain how protein binding determines drug distribution

A

⇒ In systemic circulation, many drugs are bound to circulating proteins

⇒ Most drugs must be unbound to have a pharmacological effect

⇒ The free fraction of the drug can bind to cellular receptors, then gain access to cellular enzymes

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16
Q

Once in the systemic circulation, many drugs are bound to circulating proteins.

Provide four examples of this

A
  • Albumin (acidic drugs)
  • Globulins (hormones)
  • Lipoproteins (basic drugs)
  • Acid glycoproteins (basic drugs)
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17
Q

What happens when a drug is displaced from its binding site?

A

Displacement of drugs from binding sites causes protein binding drug interactions

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18
Q

Changes in protein binding can occur, causing changes in drug distribution. However, these are only important if 3 criteria are met.

What are these criteria?

A
  • High protein binding
  • Low Vd
  • Has a narrow therapeutic ratio
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19
Q

Identify four factors which affect protein binding

A
  • Hypoalbuminaemia
  • Pregnancy
  • Renal failure
  • Displacement by other drugs
20
Q

If a drug is not bound to plasma proteins, it is available for distribution to the tissues of the body.

How can one measure the tissue distribution of a drug?

A

Volume of distribution

21
Q

What is volume of distribution?

A

Volume of distribution is a measure of how widely a drug is distributed in body tissues

22
Q

How can one calculate volume of distribution?

A

Volume of distribution (Vd) = Dose / [Drug]t0

23
Q

Identify six factors which might affect the tissue distribution of a drug

A
  • Specific receptor sites in tissues
  • Regional blood flow
  • Lipid solubility
  • Active transport
  • Disease states
  • Drug interactions
24
Q

What are the end products of drug metabolism (usually)?

A
  • After conjugation, water-soluble metabolites are formed
  • Usually, they are pharmacologically inactive
25
Q

Describe two circumstances where drug metabolism produces active metabolites

A
  • Pharmacologically inactive compound → pharmacologically active compound e.g. pro-drugs
  • Pharmacologically active compound → other active compounds eg. codeine to morphine
26
Q

Phase I metabolism involves oxidation and reduction reactions.

Which group of enzymes control these reactions?

A

Cytochrome p450 family of enzymes

27
Q

Explain how drugs can control the activity of Cytochrome P450 enzymes

A

Enzyme-inducing and enzyme-inhibiting drugs that alter the rate of metabolism of other drugs

28
Q

Identify five other factors, apart from drugs, which influences the activity of cytochrome p450 enzymes

A
  • Age
  • Liver disease
  • Hepatic blood flow
  • Cigarette use
  • Alcohol consumption
29
Q

What are Cytochrome P450 isoenzymes and what do they do?

A
  • CYP450s are a super family of isoforms responsible for approximately 90% human drug metabolism through oxidative reactions
  • They metabolise toxins such as carcinogens and pesticides
30
Q

Where are Cytochrome P450 isoenzymes found?

A

CYP450s are present mainly in the liver (some gut and lung)

31
Q

Identify 5 factors which might affect drug metabolism

A
  • Race (development of pharmacogenetics)
  • Age (reduced in aged patients & children)
  • Sex
  • Species
  • Clinical / physiological condition
32
Q

What is the main route of drug elimination?

A

The main route of drug elimination is the kidney

33
Q

Identify 5 other routes of drug elimination

A
  • Lungs
  • Breast milk
  • Sweat
  • Tears
  • Genital secretions
34
Q

Three processes determine the renal excretion of drugs.

Identify these

A
  • Glomerular Filtration
  • Passive tubular reabsorption
  • Active tubular secretion
35
Q

What is clearance?

A

Clearance is the ability of body to excrete drug (mostly = GFR)

36
Q

Describe the relationship of clearance with GFR and t1/2

A
  • GFR is directly proportional to clearance
  • t<strong>1/2</strong> is inversely proportional to clearance

i.e. a reduction in clearance (/ GFR) increases t1/2

37
Q

Describe the features of 1st Order kinetics – linear

A
  • Rate of elimination is proportional to drug level
  • Constant fraction of drug eliminated in unit time
  • t1/2 can be defined
38
Q

Describe the features of Zero Order kinetics – non-linear

A

Rate of elimination is constant

39
Q

How does one calculate the elimination rate constant (k)?

A

k = Cl / Vd

40
Q

How does one calculate half life (t1/2)?

A

t<strong>1/2</strong> = ln2 / k

41
Q

Most drugs exhibit zero order kinetics at high doses.

Why is this?

A

Because the receptors / enzymes become saturated

42
Q

Zero order drugs are more likely to result in toxicity, hence, drug monitoring essential.

Why does this occur?

A
  • Fixed rate of elimination per unit time
  • “Small” dose changes may produce large increments in [plasma] which may lead to toxicity
43
Q

Provide 5 reasons for drug monitoring

A
  • Zero order kinetics
  • Long half-life
  • Narrow therapeutic window
  • Greater risk of drug-drug interactions
  • Known toxic effects e.g. bone marrow suppression
44
Q

What is the steady state (CpSS) of the drug?

A
  • Steady state (CpSS) refers to the situation where the overall intake of a drug is in dynamic equilibrium with its elimination
  • Usually, 4-5 half lives are required to reach steady state
45
Q

Loading doses are employed to reach CpSS more rapidly.

What are loading doses?

A
  • A loading dose is an initial higher dose of a drug that is given at the start of a drug course before dropping down to a lower maintenance dose
  • Useful for drugs that have a long systemic half-life (eliminated slowly)
46
Q

How does one calculate loading doses?

A

Loading Dose = Vd x [Drug]target

(LUSUMA) Clinical Pharmacology & Therapeutics (29 decks)

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