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Semester 4 - Clinical Pharmacology And Therapeutics > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

What the body does to a drug.

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2
Q

What are the main components of pharmacokinetics?

A

Absorption
Distribution
Metabolism
Elimination

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3
Q

What are the key factors of pharmacokinetics?

A 
Bioavailability 
Half-life 
Drug elimination
Intra-subject variability
Drug-drug interactions
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4
Q

What things should you consider then thinking about PK?

A 
Renal function
Stress
Pyrexia
Alcohol
Smoking 
Age
Sex
Exercise
Infection
Diet
Occupational exposure
Lactation
Liver function
Albumin conc.
CV function
Carcadian and seasonal variations
Immunisation
Barometric pressure
GI function
Pregnancy
Infection
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5
Q

What are the four parts of drug therapy?

A

Pharmaceutical prep
Pharmacokinetic process
Pharmacodynamic process
Therapeutic process

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6
Q

What is bioavailability (F)?

A

Measure of drug absorption into body compartment where it can used - typically circulation

Drug administered via IV bolus is said to have 100% bioavailability.

Other routes of administration referenced as a fraction of i.v

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7
Q

What factors affect bioavailability?

A 
Absorption:
Formulation
Age (luminal changes)
Food (chelation, gastric emptying)
Vomiting / malabsorption

First pass metabolism:
Metabolism before reaching systemic circulation (gut lumen, gut wall, liver)

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8
Q

What are modified release preparation?

A

Those which release the drug slowly and so, remain within the therapeutic range for longer.

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9
Q

What factors affect how well the drug dissolved and distributes through the interstitium?

A

Blood flow, capillary structure

Lipophilicity vs hydrophilicity

Protein binding (albumin)

Volume of Distribution

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10
Q

Displacement of a drug from binding site can result in protein bringing drug interactions. When is this clinically important?

A

Highly protein bound
Narrow therapeutic index
Low Vd

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11
Q

What effect does increasing free drug have on drug-protein binding and distribution?

A

Will be able to afford response and / or be eliminated.

Second drug displaced first drug from binding proteins.

More free first drug to elicit a response through receptor.

Potentially causing harm - entering toxic dose concentration.

Pregnancy (fluid balance), renal failure, hypoalbuminemia (malnutrition) among others.

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12
Q

what is the volume of distribution?

A

Vd is typically hypothetical measure of how widely a drug is distributed in the body (apparent Vd)

Vd = dose / [drug]plasma

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13
Q

When is Vd useful?

A

Estimating dishing regiments.

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14
Q

What does a Vd mean?

A

Small Vd - drug confined to plasma and ecf

Larger Vd - drug is distributed throughout the tissues.

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15
Q

What is Vd proportional to?

A

Half life

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16
Q

Describe the phases of metabolism in the liver?

A

Drug

Phase I enzymes + CYPs - oxidation, dealkylation, reduction hydrolysis

Phase II enzymes - Glucuronide, sulphate glutathione, N-acetyl
Conjugates

Then go to other sites (kidney to urine or gall bladder to bile)

17
Q

What things affect the route and mechanism of metabolism of a drug?

A

Size
Lipophilicity
Hydrophobicity
Structural complexity

18
Q

What things inhibit CYP3A4?

A

Grapefruit juice and statin therapy.

19
Q

What is CYP 2D6?

A

Absent in 7% of Caucasians.

Hyperactivity / increased induction in 30% East Africans

Substrates include some anti arrhythmias, antidepressants and opioids.

Inhibited by some SSRIs, other anti arrhythmias and other antidepressants.

20
Q

What is the clinical importance of having different CYPs?

A

Important for drug prescribing

Need to consider OTC and food as drug-drug interactions.

Also consider:
Race
Age
Sex
Species
Clinical or physiological condition
21
Q

How are drugs removed from the body?

A

Mostly via the kidney (25% of systemic blood flow)

Other possible routes: pulmonary, biliary, faecal, sweat, genital, secretions, saliva, breast milk

22
Q

What affects drug elimination?

A

GFR and protein binding (gentamicin)
Competition for transporters (penicillin)
Lipid solubility, pH, flow rate (aspirin)

23
Q

What is clearance?

A

Clearance of drug from the body is the rate of clearance from all routes - both metabolism and excretion taken together. (Mostly GFR)

24
Q

What is half life?

A

Time is which concentration of a drug in plasma decreases by half

25
Q

When will half life increase?

A

If GFR is reduced then clearance is compromised and half life increased. (half time is inversely proportional to clearance).

Also increased in:
Renal or hepatic stenosis
Haemorrhage
Reduced metabolism
Reduced plasma drug extraction
Drug-drug interactions.
26
Q

What is 1st and 0 order kinetics?

A

1st order - rate of elimination is proportional to drug concentration

0 order - rate of elimination is a constant

27
Q

What is Half life proportional to?

A

Vd (volume of distribution)

28
Q

What is half life inversely proportional to?

A

Cl (clearance)

29
Q

What order kinetics do most dugs exhibit?

A

First order kinetics

30
Q

What drugs do not exhibit first order Kinetics and what effect does this have?

A

Ethanol. Aspirin, phenytoin (unpredictable).

This is important as the dose change can produce unpredictable change in plasma so half life in not calculable.

31
Q

What particular characteristics mean the drug needs careful monitoring.

A 
PK
Zero order kinetics
Long half-life
Narrow therapeutics window 
Drug-drug interaction
Reported or expected toxic effects
Therapeutic effect
32
Q

When is the steady state plasma conc reached?

A

5 half lives

Same amount of half lives to eliminate dugs.

The therapeutic benefit is optimal at a steady state.

33
Q

What things do you have to consider when doing half life?

A

Dosing schedule

34
Q

Other than half life, what other things do you need to know to work out the dosing schedule?

A

Age (muscle mass)
Adipose tissue (Vd changes)
Pathological fluid spaces among others

Semester 4 - Clinical Pharmacology And Therapeutics (26 decks)

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