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Pharm > Lecture 4: How Drugs are Eliminated (Pharmacokinetics) > Flashcards

Lecture 4: How Drugs are Eliminated (Pharmacokinetics) Flashcards

1
Q

What are the main categories of Pharmacokinetics?

A

Absorption, Distribution, Metabolism, Excretion

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2
Q

Why do the effects of a drug wear off?

A

Because over time the drug is eliminated from the body

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3
Q

What are the characteristics of a drug that is absorbed faster?

A

It will reach its peak effect faster, but because it gets into the bloodstream faster it will be eliminated sooner and have a shorter duration of effect

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4
Q

What are the characteristics of a drug that has a larger dose?

A

It would be absorbed faster and have a higher peak effect and it would have a longer duration of action because it takes longer to be eliminated

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5
Q

What are the characteristics of a drug that is eliminated more quickly from the body?

A

It would appear to have a smaller peak effect because it being eliminated quicker

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6
Q

What can profile of the amount of drug in our body overtime be controlled by?

A

By manipulating properties of the drug or the different properties in the body

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7
Q

Why is it important to understand pharmacokinetic principles?

A

Because they define how often or how much of a drug you should be taking to be at its optimal concentration in the body

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8
Q

Which questions do drug parameters influence?

A
  • How much drug should be taken?
  • How often?
  • how long will it take me to perceive an effect of the drug?
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9
Q

What are the three considerations for the route of administration of a drug?

A
  • Convenience
  • Bioavailability
  • Processing
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10
Q

Why is convenience an important consideration for drug administration?

A

Because it is easier to take a medication orally vs through an injection, IV or other routes

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11
Q

Why is bioavailability an important consideration for drug administration?

A

Because difference drugs may be absorbed with different efficiency from the gut

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12
Q

Why is Processing an important consideration for drug administration?

A

Because drugs that are absorbed from the gut first encounter the liver before entering systemic circulation so there is sometimes significant processing and breakdown

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13
Q

Where do drugs that are absorbed in the gut go before reaching the systemic circulation?

A

They go through hepatic portal circulation and to the liver

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14
Q

Why is the liver of important consideration with drugs?

A

Because it is a major site of metabolism and strongly influences the bioavailability of drugs

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15
Q

What is First Pass Metaolism?

A

The amount of a drug that is processed or eliminated its first time through through the liver after it is absorbed in the gut and goes through the circulatory system

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16
Q

What is the inverse of bioavailability?

A

Extractions ratio

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17
Q

What is Clearance?

A

The volume of blood that can be cleared of a compound over a certain amount of time

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18
Q

Why would something have a higher clearance?

A

The more effectively something is removed from the blood by the liver the higher the clearance and the higher the extraction ratio

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19
Q

What drugs have a high extraction ratio?

A

Drugs that are rapidly processed by the liver

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20
Q

What is the meaning of a low extraction ratio?

A

Drugs that a poorly processes by the liver (aren’t significantly processed by the liver)

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21
Q

What are the six routes of administration?

A
  • Oral
  • Intravenous
  • Intramuscular/subcutaneous
  • Inhalation
  • Sublingual
  • Transdermal
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22
Q

What is the rate of adsorption for Oral drugs?

A

Slow

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23
Q

What can Oral drugs be affected by?

A

Intake of food

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24
Q

What can the exposure of oral drugs be influenced by?

A

Breakdown in the gut and processing in the liver

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25
Q

What is the rate of the onset of action of intravenous drugs and why?

A

They have a very rapid onset because it is delivered directly into the systemic system

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26
Q

Why is intravenous not often used?

A

Because it is inconvenient and requires expertise

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27
Q

What are the pros to intravenous injections?

A
  • Rapid onset

* There is high control over circulating level by controlling the rate of infusion

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28
Q

What does the rate of absorption of intramuscular injections depend on?

A

Blood flow to the site

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29
Q

What is a common type of intramuscular injection?

A

Depot injections for sustained release

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30
Q

What are Depot injections?

A

Intramuscular injections that slowly dissolve for sustained release

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31
Q

Where is absorption in inhalation administration?

A

The epithelium in the lungs, and can be very rapid

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32
Q

What is the rate of absorption in sublingual administration?

A

Rapid absorption route

33
Q

What does Sublingual administration bypass?

A

Bypasses the ‘first pass’ effects despite being taken orally

34
Q

What are the benefits to Transdermal (Ointment or patch) administration?

A

Convenient, slow absorption and sustained exposure

35
Q

What is Bioavailability?

A

The fraction of unprocessed/unaltered drug that reaches the systemic circulation after administration by a particular route

36
Q

What is the bioavailability of IV administration?

A

100%

37
Q

What are the very efficient route of administration in terms of bioavailability?

A

IV, Intramuscular (IM), and Subcutaneous (SC)

38
Q

Which administration has the most variable bioavailability?

A

Oral administration because of first pass

39
Q

What does Distribution refer to?

A

How a drug or substance is partitioned into different body compartments after it is absorbed

40
Q

What does the distribution of a drug have an influence on?

A

The effective concentration of a drug in the body and its lifetime of the drug in the body

41
Q

What are the two key factors to drug distribution?

A
  • Binding to plasma proteins

* Drug accumulation in tissues

42
Q

What do drugs circulate in the equilibrium between?

A

Free and bound to some globulin in the bloodstream

43
Q

Which drugs are considered pharmacologically active in terms of free and bound?

A

Only free drugs

44
Q

Why are only free concentrations of drugs considered pharmacologically active?

A

Because bound drugs are unable to interact with the receptor

45
Q

What are the characteristics of drugs that are highly bound to blood globulins?

A

They have a long lifetime in the body but have a smaller concentration that is able to interact with receptors

46
Q

What kind of drugs is drug accumulation favored for?

A

Drugs that are lipophilic

47
Q

Which tissues can accumulate a drug more readily?

A

More highly perfused tissues

48
Q

Why can highly lipophilic drugs accumulate in tissues?

A

Because they can easily cross cell membranes

49
Q

What is the meaning of a high volume of concentration?

A

The drug will have a high concentration in body compartments relative to the bloodstream

50
Q

What is the meaning of a low volume of concentration?

A

A drug is restricted to the bloodstream and does not distribute to the compartments well

51
Q

What drugs will have a VOD close to blood volume?

A

Drugs that a restricted to the circulation/plasma

52
Q

What kind of drugs will have a high volume of distribution?

A

Drugs that distributes throughout the entire body water

53
Q

Why would a drug have a really large VOD?

A

Because the drug is highly lipophilic and accumulates in fat tissue

54
Q

How can drugs that a poorly lipid soluble distribute?

A

Through extracellular fluid

55
Q

What would cause a drug to be entirely restricted to the blood circulation or plasma?

A

Because it is bound to plasma proteins

56
Q

What is Single compartment distribution?

A

When a drug is contained within a single compartment

57
Q

What is drug elimination like in single compartment distribution?

A

The drug concentration decreases with exponential decay

58
Q

What occurs after administration in multiple compartment distribution?

A

The drug distributes into multiple compartments (blood and tissue)

59
Q

How does elimination work in multiple compartment distribution?

A

The drug concentration in the blood can be eliminated but the reservoir (other compartments) can prolong the lifetime of the drug in the body

60
Q

How does the distribution of a drug into compartments affect the rate at which it is eliminated?

A

Drugs that move into compartments from the bloodstream are eliminated at a lesser rate than those that do not

61
Q

What is Biotransformation?

A

Drug metabolism in the liver

62
Q

What are the key mechanisms leading to elimination?

A

Metabolism in the liver and excretion (kidney/gut)

63
Q

What does metabolism in the liver involve?

A

Phase 1 and Phase 2

64
Q

What occurs in Phase 1?

A

Mixed Function Oxidase system (CYP family enzymes) generate oxidative modifications of drugs

65
Q

What occurs in Phase 2?

A

Conjugation of parent compound or Phase 1 product with large polar adducts to make the product more prone to excretion

66
Q

What is the most important CYP?

A

CYP3A4

67
Q

What kinds of drugs can be excreted?

A

Modified and unmodified

68
Q

How many CYP genes can metabolize a drug?

A

Multiple

69
Q

What leads to individual differences in how we respond to drugs?

A

Genetic variation in CYP enzymes

70
Q

What can cause Hepatotoxicity?

A

When sometimes toxic/reactive intermediates are formed by CYP proteins interacting with drugs

71
Q

Why is it possible to overdose on acetaminophen?

A

If there is a shortage of phase 2 compounds then a lot of it gets processed into intermediate forms by phase 1 this can cause cell death in the liver

72
Q

What are the primary routes for excretion after metabolism?

A
  • Bile/Feces

* Urine

73
Q

How are Biotransformed drugs excreted through urine and feces?

A

Drugs in the liver are incorporated into bile and secreted into the gut

74
Q

Why don’t drugs in bile become reablsorbed?

A

Modifications add large polar adducts and make the drugs more polar and less prone to be reabsorbed in the digestive tract

75
Q

How do excreted drugs make it to the urine?

A

The drug passes through glomerular filtration or is actively secreted into the renal tubule

76
Q

What is overall drug elimination described by?

A

A half life

77
Q

How is a higher concentration of a drug affected by elimination?

A

A higher concentration of a drug has a high rate of elimination

78
Q

What is Capacity Limited elimination?

A

When the concentrations of a drug are much higher than the affinity of a key enzyme involved in their elimination

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