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ESA 5 > CPT S1 - Pharmacokinetics 1 > Flashcards

CPT S1 - Pharmacokinetics 1 Flashcards

1
Q

Define pharmacodynamics

A

The study of the drug mechanisms of action and effects on the body. “What the drug does to the body”

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2
Q

Define pharmacogenetics

A

The effect of genetics on the kinetics and dynamics of the drug on an individual

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3
Q

Define pharmacokinetics

A

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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4
Q

What are the key factors of pharmacokinetics?

A 
Bioavailability 
Half life
Drug elimination
Intra-subject variability
Drug to drug interactions
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5
Q

What are the processes of pharmacokinetics?

A

Absorption
Distribution
Metabolism
Elimination

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6
Q

Define bioavailability

A

The proportion of a dose which finds itself in a body compartment, usually circulation. IV plasma bioavailability is 100% so other routes of administration are compared to this.

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7
Q

What factors affect bioavailability?

A 
Drug formulation (sustained release etc.)
Age
Malabsorption (eg in Crohn's disease)
Food - (lipid soluble?)
First pass metabolism
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8
Q

Where can first pass metabolism occur?

A

The gut lumen
The gut wall
The liver

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9
Q

Define first pass metabolism

A

Any metabolism occurring before the drug enters systemic circulation

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10
Q

Give an example of first pass metabolism in the gut lumen

A

Denature due to gastric acid, proteolytic enzymes, grapefruit juice.

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11
Q

Give an example of first pass metabolism in the gut wall

A

Efflux pumps to move the drug back into the gut lumen from the enterocytes.

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12
Q

Give an example of first pass metabolism in the liver

A

Many enzymes including the CYP450 family metabolise drugs extensively and contribute to the first pass effect

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13
Q

Define drug distribution

A

The ability of a drug to dissolve in the body

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14
Q

What key factors affect the distribution of a drug?

A

Protein binding

Volume of distribution (Vd)

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15
Q

Give examples of proteins that drugs can bind to in circulation

A

Albumin (acidic drugs)
Globulins (hormones)
Lipoproteins (basic drugs)
Glycoproteins (basic drugs)

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16
Q

Why is protein binding an important factor?

A

Most drugs have to be free/unbound to have their desired pharmacological effect.

17
Q

Multiple drugs in circulation may bind to the same proteins, causing changes in drug distribution. In what circumstances is this clinically relevant?

A

There is high protein binding
Low Vd
A narrow therapeutic ratio

18
Q

What are some factors affecting protein binding?

A

Hypoalbuminaemia
Pregnancy
Renal failure
Displacement by other drugs

19
Q

What can affect tissue distribution?

A 
Specific receptor types within the tissue
Regional blood flow
Lipid solubility
Active transport
Disease States
Drug interactions
20
Q

What are active metabolites?

A

The products of the phase I enzymes of the drug metabolism in the liver. Sometimes, the active compound which has the desired pharmacological effect is produced from a precursor or pro-drug, eg codeine, losartan.

21
Q

Give examples of foods and OTC medications which can interact with prescription drug metabolism

A

Charcoal grilled food consumption is a CYP inducer
Grapefruit juice is a CYP inhibitor
St. John’s Wort is another inhibitor

22
Q

What can affect drug metabolism?

A

Ethnicity (genetic variability)
Age (lower doses for the very old and very young)
Sex (women slower ethanol metabolisers)
Species (drug development)
Clinical or physical condition (eg hypo/eralbuminaemia)

23
Q

Where is the biggest route of drug elimination?

A

The kidney

24
Q

Which processes determine the renal excretion of drugs?

A

Glomerular filtration
Passive tubular reabsorption
Active tubular secretion

25
Q

Define 1st order kinetics

A

Rate of elimination is proportional to the drug level.
Constant fraction of the drug is eliminated per unit time.
Half life can be defined.

26
Q

Define zero order kinetics

A

Rate of elimination is a constant.

Almost all drugs exhibit zero order kinetics at high enough doses as receptors become saturated

27
Q

Why is zero order kinetics more dangerous?

A 
More likely to result in toxicity
Fixed rate of elimination
Small dose changes can produce large changes in plasma concentration
No half life is calculable
Drug monitoring is essential
28
Q

In what circumstances might you monitor a patient’s plasma drug concentration?

A 
Zero order kinetics
Long half life
Narrow therapeutic window
High drug to drug interaction profile
Known toxic effect
In order to monitor therapeutic effect (BP, glucose)
29
Q

How long does it take for a new drug to reach a steady state in the plasma?

A

3-5 half lives, irrespective of dose frequency or administration

ESA 5 (17 decks)

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