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17. Clinical Pharmacology and Therapeutics > 1 and 2. Pharmacokinetics > Flashcards

1 and 2. Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

The study of a drug into and out of the body considering 4 main mechanisms (absorption, distribution, metabolism, and elimination).

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2
Q

What are the four main mechanisms in pharmacokinetics?

A

Absorption, distribution, metabolism, elimination.

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3
Q

What can affect peak plasma concentration of a drug in oral administration?

A

Rate of uptake of the drug and first pass metabolism.

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4
Q

What can affect the systemic entry of a drug?

A

GI motility, splanchnic blood flow, molecule size, pH levels, presence of active transport systems.

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5
Q

What is first pass metabolism?

A

Metabolism occurring before a drug enters the systemic circulation. Mostly in liver and portal venous system.

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6
Q

What is the effect of first pass metabolism?

A

Significantly reduced amounts of available drug in systemic circulation.

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7
Q

What is bioavailability?

A

Amount of drug which reaches the systemic circulation in an unchanged form relative to if administered via IV.

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8
Q

How is bioavailability calculated?

A

Amount of drug reaching systemic circulation/total amount of drug administered.

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9
Q

What is bioavailability affected by?

A

Drug preparation, intestinal motility, food, age, and first-pass metabolism.

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10
Q

What is drug distribution?

A

Ability of a drug to dissolve in the body.

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11
Q

What are the main factors affecting distribution throughout the body?

A

Lipophilicity/hydrophilicity and protein binding.

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12
Q

How does lipophilicity/hydrophilicity affect drug distribution?

A

If more lipophilic, more partitions out of the blood plasma into tissues with higher lipid content so if lipid-insoluble, then confined to plasma and interstitial fluid.

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13
Q

How does protein binding affect drug distribution?

A

Most drugs have to be unbound to have effect but most drugs are protein bound in circulation.

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14
Q

How do object and precipitant drugs differ?

A

Object - numbers of drugs less than binding site numbers.

Precipitant - number of molecules administered higher than binding sites.

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15
Q

How do precipitant drugs affect object drugs?

A

They displace molecules so free concentration of object drug increases.

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16
Q

How can protein binding be changed?

A

Hypoalbuminaemia, pregnancy, renal failure, displacement by other drugs.

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17
Q

When is changes to protein binding a problem?

A

If high protein binding normally, low volume of distribution, and narrow therapeutic ratio.

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18
Q

What are the two main separate body compartments?

A

Extracellular fluid compartment and intracellular fluid compartment.

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19
Q

What does the ECF compartment comprise of?

A

Plasma, interstitial fluid, transcellular fluid, and fat.

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20
Q

What does the apparent volume of a drug depend on?

A

Binding capacity there is for a given drug.

21
Q

What is the volume of distribution?

A

Measure to see how well a drug distributed throughout body systems.

22
Q

How is volume of distribution calculated?

A

Total amount of drug in the body/plasma concentration of drug (at time = 0).

23
Q

What is the effect of being lipid soluble on volume of distribution?

A

It can leave plasma into other fluid compartments so volume of distribution is higher.

24
Q

What is volume of distribution proportional to?

A

Half life.

25
Q

What is volume of distribution affected by?

A

Lipid solubility, protein binding, disease states, regional blood flow, specific receptor sites in tissues.

26
Q

When are acute increases in volume of distribution seen?

A

In sepsis, concurrent drugs, hypoalbuminaemia.

27
Q

What are the phases of metabolism?

A

1 - catabolic reactions -> products that are chemically active.
2 - anabolic reactions with conjugation -? inactive products.

28
Q

How do the phases of metabolism affect lipid solubility and therefore renal elimination?

A

Decreases lipid solubility so increases renal elimination.

29
Q

Where do the phases of metabolism mainly occur?

A

Liver.

30
Q

What enzyme family does phase 1 of metabolism depend on?

A

Cytochrome P450.

31
Q

What affects CYP450 activity?

A

Drugs, age, liver disease, hepatic flow.

32
Q

What are CYP enzymes?

A

Haem protein in the liver.

33
Q

What induces CYP enzymes?

A

PCBRAS - phenytoin, carbamazapine, barbiturates, rifampicin, alcohol, sulphonylureas.

34
Q

What inhibits CYP enzymes?

A

O-DEVICES - omeprazole, disulfiram, erythromycin, valproic acid, isoniazid, cimetidine, ethanol, sulphonamides.

35
Q

What is the main route of drug elimination?

A

Via the kidney.

36
Q

What are minor routes of drug elimination?

A

Lungs, breast milk, sweat, tears, genital secretions, bile, and saliva.

37
Q

What are the three processes determining rate of renal excretion of drugs?

A

GFR, passive tubular reabsorption, and active tubular secretion.

38
Q

What is clearance a measure?

A

Hepatic clearance and renal clearance.

39
Q

How do organic anion and cation transporters contribute to drug elimination?

A

Act as renal transporters and transport drugs from plasma to nephron lumen, they’re in the PCT.

40
Q

What affects clearance rate?

A

Heart (CVS affects blood flow to main organs of elimination), renal (affects renal elimination), hepatic (affects hepatic elimination).

41
Q

What is the half life of a drug?

A

The amount of time over which the concentration of a drug in plasma decreases to one half of the concentration value it had when measured.

42
Q

What affects the half life of a drug?

A

Cardiovascular factors, renal elimination, and hepatic metabolism.

43
Q

What is 1st order kinetics?

A

Rate of elimination is proportional to drug level so a constant fraction of drug is eliminated in unit time.

44
Q

What is zero order kinetics?

A

Rate of elimination is constant and no half life can be defined.

45
Q

How can steady state concentration in plasma be calculated?

A

CpSS = dose rate/clearance.

46
Q

When is CpSS reached?

A

4-5 half lives.

47
Q

What is the purpose of a loading dose?

A

A clinician wants to achieve a CpSS within the therapeutic window quickly.

48
Q

How is loading dose calculated?

A

DoseL = Vd x CpSS.

17. Clinical Pharmacology and Therapeutics (25 decks)

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