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Pharmacology I > 1 - Pharmacokinetics > Flashcards

1 - Pharmacokinetics Flashcards

1
Q

What is prescriptive authority?

A

The legal right to prescribe drugs

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2
Q

What does it mean to prescribe independently?

What does it mean to prescribe without limitation?

A
  1. Doesn’t need MD approval
  2. Can prescribe any meds except schedule 1 drugs
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3
Q

What are schedule 1 drugs?

A

Ecstasy, Meth, Heroin, Marijuana, LSD

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4
Q

What are the nine essential components of medication educaction?

A
  1. Name
  2. Purpose
  3. Dosing Regimen
  4. Administration
  5. Adverse Effects
  6. Storage
  7. Lab Testing
  8. Interactions
  9. Duration of therapy
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5
Q

What are the three purposes of drug monitoring?

A

Determining Therapeutic Dosage

Evaluating medication adequacy

identifying adverse effects

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6
Q

What does it mean if a drug has an NTI?

A

It has a narrow therapeutic index

(coumadin, lithium, theophylline)

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7
Q

What is the most common nonadherent behavior?

A

Missed a dose (57%)

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8
Q

What are the six nonadherent behaviors?

A
  1. Missed a dose
  2. Forgot to take a dose
  3. Didn’t refill in time
  4. Took less than prescribed
  5. Didn’t refill at all
  6. Stopped taking the med
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9
Q

What are the four most common reasons for nonadherence?

A
  1. Forgot (42%)
  2. Ran Out (34%)
  3. Away from home (27%)
  4. Trying to save money (22%)
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10
Q

What are the four basic principles of pharmacokinetics

A

Absorption

Distribution

Metabolism

Excretion

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11
Q

What is absorption?

A

Drug’s movement from site of administration into the blood

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12
Q

What is distribution?

A

Drug’s movement from blood into interstitial space and then into cells

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13
Q

What is metabolism?

A

i.e. biotransformation

enzymatically mediated alteration of drug structure

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14
Q

What is elimination?

A

The combination of metabolism and excretion

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15
Q

What are the three modes by which drugs cross the cell membrane?

Which is most common?

A

Channels/Pores

Transport System

Direction Penetration (Most common)

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16
Q

How common is it for drugs to pass through pores or channels?

A

Extremely uncommon

Pores and channels are very specific

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17
Q

All transport systems are _____

A

selective

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18
Q

What is PGP?

A

AKA P-glycoprotein or multidrug transporter protein

One of the most prolific drug transport proteins

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19
Q

Why do most drugs depend on direct penetration to get through membranes?

A

Most drugs are too large to pass through pores/channels

AND

most drugs lack transport systems

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20
Q

What kind of drug is most likely to successfully achieve direct penetration?

Why?

A

Lipid soluble drugs

Membranes are composed primarily of lipids, and like dissolves like

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21
Q

What are polar molecules?

A

molecules with no net charge but an uneven distribution of electrical charge

Positive and negative charges on the molecule congregate separately, so there is a (+) and (-) end..

TWO POLES

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22
Q

Is water polar or nonpolar?

Are lipids polar or nonpolar?

A

Polar

Nonpolar

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23
Q

Polar molecules will dissolve in _____ solvents

A

Polar

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24
Q

What are ions?

A

Molecules that have a net electrical charge

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25
Q

Many drugs are either weak acids or weak bases. Why is that significant?

A

They can exist in charged and uncharged forms

Weak acids and bases carry electrical charges based on the pH of the medium

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26
Q

Acids tend to ionize in _____ media

Bases tend to ionize in ____ media

A

basic

acidic

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27
Q

Drugs that are weak acids are best absorbed in ____ environments

A

Acidic BECAUSE they remain in a non-ionized form

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28
Q

What is pH partitioning or ion trapping?

A

When a membrane has an acidic side and a basic side, drug molecules will accumulate on the side where the pH most favors their ionization

Acidic drugs accumulate on the alkaline side

Alkaline drugs accumulate on the acidic side

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29
Q

What are chemically equivalent drug preparations?

A

ones that contains the same amount of of the identical chemical compound

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30
Q

Preparations are considered equal in bioavailability when:

A

the drug they contain is absorbed at the same rate and to the same extent

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31
Q

What factors affect drug absorption?

A
  1. Rate of dissolution (how quickly it dissolves)
  2. Surface area available for absorption (higher in the SI than the stomach, for example)
  3. Blood Flow
  4. Lipid Solubility
  5. pH partitioning
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32
Q

As a rule, highly lipid-soluble drugs are absorbed _____

A

more rapidly than drugs with a low lipid solubility

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33
Q

How does pH partitioning influence drug absorption?

A

Absorption is enhanced with the difference between the pH of the plasma and the pH at the site of administration is such that drug molecules will have a greater tendency to be ionized in the plasma

If the plasma is more basic than the site of administration, and the medication is a weak acid, the medication is more likely to ionize and get “trapped” in the plasma

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34
Q

What three factors determine drug distribution?

A
  1. Blood flow to tissues
  2. Ability of a drug to exit the vascular system
  3. Ability of a drug to enter cells
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35
Q

Since most tissues are well perfused, distribution is seldom a limiting factor for drug delivery. When is this not true?

A

Abscesses and Tumors

An abscess has no internal blood vessels, so ABX can’t reach it. That’s why they have to be drained.

Solid Tumors have a limited blood supply on the INSIDE. Can make chemo therapy minimally effective

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36
Q

Why is it so easy for drugs to pass through capillaries?

Where is this not true?

A

They simply pass through the pores in the capillary walls in between capillary cells (rather than through them)

The brain and the placenta

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37
Q

Only drugs that are ____ or ____ can cross the Blood Brain Barrier

A

Lipid soluble

have a transport system

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38
Q

Why is the blood brain barrier so impermeable to most drugs?

A

Tight cell junctions

PGP pumps drug back into the blood from capillary cells, limiting the amount that can get through to the brain

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39
Q

Why are newborns so susceptible to medications with CNS toxicity?

A

The BBB is not fully developed at birth

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40
Q

Most drugs cross the placenta via _______

A

simple diffusion

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41
Q

What kind of drugs pass easily from the maternal bloodstream into fetal blood supply?

A

lipid soluble, non-ionized compounds

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42
Q

What kind of drugs have a hard time passing through the placental membrane?

A

compounds that are ionized, highly polar, or protein bound

drugs that are substrates for the PGP transporter (which pumps the drug back out into maternal circulation)

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43
Q

What is the most important protein drugs may bind to?

A

Albumin

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44
Q

What determines the percentage of drug molecules that circulate bound to albumin?

A

The strength of the attraction between albumin and the drug

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45
Q

How does albumin contribute to drug interactions?

A

Each albumin only has a few binding sites

Drugs that bind with albumin compete for these sites and can displace one another

Giving one drug with a high affinity for albumin may decrease the albumin binding of another drug, dramatically increasing its free concentration and effect

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46
Q

Where does most drug metabolism take place?

A

The liver

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47
Q

Most drug metabolism that takes place in the liver is performed by:

A

the p450 system

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48
Q

What is cytochrome p450?

A

It is NOT a single molecule! It is a group of 12 closely related CYP enzyme families

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49
Q

Which p450 families metabolize drugs?

A

CYP1

CYP2

CYP3

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50
Q

If three p450 families metabolize drugs, what do the other 9 do?

A

metabolize endogenous compounds (steroids, fatty acids, etc)

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51
Q

What are the six functions/consequences of drug metabolism?

A
  1. Enables renal excretion
  2. Drug inactivation
  3. increased therapeutic action
  4. activation of prodrugs
  5. increased or decreased toxicity
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52
Q

What is the most important consequence of drug metabolism?

A

promotion of renal excretion

lipid soluble drugs have to metabolized into hydrophilic forms before the kidneys can excrete them

53
Q

what is the most common end result of drug metabolism?

A

inactivation

54
Q

Give an example of metabolism that causes increased therapeutic action

A

Codeine is metabolized into morphine, which is much, much more analgesic

55
Q

What is a prodrug?

A

A drug that is pharmacologically inactive until it is metabolized into its active form in the body

56
Q

What are some advantages to prodrugs?

A

a drug that can’t ordinarily cross the BBB can be administered as a lipid-soluble prodrug that is converted to the active form once inside the CNS

57
Q

What is an example of increased toxicity from metabolism?

A

It’s actually the metabolites of tylenol that are lethal to the liver, not the tylenol itself

58
Q

What factors influence the rate of drug metabolism?

A

Age

Induction and Inhibition of Enzymes

First-Pass Effect

Nutritional Status

Competition between drugs

59
Q

Drugs that are metabolized by P450 hepatic enzymes are called ______

A

p450 substrates

60
Q

Drugs that increase the rate of drug metabolism are _____

A

p450 inducers

61
Q

Drugs that decrease the rate of drug metabolism are ______

A

p450 inhibitors

62
Q

How do drugs that are p450 inducers effect metabolism?

A

act on the liver to stimulate enzyme synthesis

Decreases the amount of active drug and plasma levels fall

63
Q

What is the first-pass effect?

A

the rapid hepatic inactivation of certain ORAL drugs

64
Q

Why is first-pass effect only a factor with oral medications?

A

When drugs are absorbed through the gut, they go through portal circulation before they enter the systemic circulation

65
Q

Drugs that undergo rapid hepatic metabolism often must be given ______

A

parenterally, in order to avoid the first-pass effect

66
Q

Why does nutritional status effect drug metabolism?

A

drug-metabolizing enzymes require a lot of cofactors which are mostly obtained via nutrition

Without them, drug metabolism is impaired

67
Q

What is enterohepatic recirculation?

A

When a drug is absorbed through the gut, is transported to the liver via portal circulation, the liver transports it into the bile duct, and it returns to the duodenum. Then the process repeats.

68
Q

Which drugs are effected by enterohepatic recirculation?

A

Drugs that have undergone glucuronidation (a process that coverts lipid soluble drugs to water soluble drugs by binding them to glucuronic acid)

It causes these drugs to be present in the body much longer than they otherwise would

69
Q

What are the 6 modes of excretion?

A
  1. Urine
  2. Bile
  3. Sweat
  4. Saliva
  5. Breast Milk
  6. Exhalation
70
Q

Which organ accounts for the majority of drug excretion?

A

Kidneys

71
Q

What factors modify renal drug excretion?

A
  1. pH dependent ionization
  2. competition for active tubular transport
  3. Age
72
Q

Which drugs undergo passive tubular reabsorption?

A

ONLY lipid soluble drugs

73
Q

Why can manipulating urinary pH change excretion?

A

Drugs that are ionized at the pH of urine will ionize within the tubule and will not reabsorb

If you alter the urine’s pH to promote ionization of the drug, it will be excreted much more effectively

This has been used to promote excretion of poisons and medications that have been taken in toxic doses

74
Q

If you give two drugs that have the same active excretion system, what will happen?

A

The excretion time of each will be delayed because they’re competing for excretion

75
Q

Which drugs are most likely to pass into breast milk?

A

The same principles apply here as for any other membrane:

Lipid soluble drugs pass easily

Drugs that are polar, ionized, or protein bound do not

76
Q

What does a plasma drug level tell us?

A

It tells us the amount of drug in the blood, but NOT the amount of drug at the site of action

We know from experience that there is a direct correlation between therapeutic and toxic responses and the amount of drug present in plasma

We know which plasma drug concentration are highly predictive of therapeutic and toxic responses

77
Q

What are the two plasma drug levels?

A
  1. minimum effective concentration
  2. toxic concentration
78
Q

What is minimum effective concentration?

A

the plasma drug level less than which therapeutic effects will not occur

79
Q

The therapeutic range falls between ____ and ___

A

MEC and Toxic Concentration

80
Q

Which is more dangerous, a narrow therapeutic range or a wide therapeutic range?

A

Narrow

81
Q

The latent period of a drug (between administration and onset of effects) is determined by:

A

the rate of absorption

82
Q

The duration of a drug is determined by:

A

metabolism and excretion

83
Q

What is drug half life?

A

the time required for the amount of drug in the body to decrease by 50%

84
Q

Does every drug have a half life?

A

No. Some drugs (like ethanol) leave the body at a constant rate, regardless of how much is present

85
Q

What causes a plateau in drug levels, even when successive doses are administered?

A

Eventually the amount of drug eliminated between doses equals the dose administered, and the average drug level remains constant

86
Q

When a drug is administered repeatedly in the same dose, when will a plateau be reached?

A

After four half lives

87
Q

How does the size of the dose impact the time required to reach a plateau?

A

As long as the dose is constant, the plateau time will always be four half lives, regardless of the size of the dose

88
Q

What are three techniques that can be used to reduce fluctuations in drug levels?

A

Continuous infusion

Administer a depot preparation (slow release)

Reduce both the size of dose and dose interval

89
Q

What is the purpose of a loading dose?

A

To reach a plateau in less than four half lives

90
Q

What is pharmacodynamics?

A

the effects of drugs and the molecular mechanisms that cause those effects

91
Q

Dose-response curves reveal two characteristic properties of drugs:

A
  1. maximal efficacy
  2. Relative Potency
92
Q

What is maximal efficacy?

A

the height of the dose-response curve

the largest effect that a drug can produce

93
Q

What is relative potency?

A

the amount of the drug that must be given to elicit an effect

the relative position of the dose-response curve along the x (dose) axis

94
Q

How are efficacy and potency related?

A

They aren’t!

Potency and efficacy are completely independent. Drug A can be more effective than Drug B even though Drug B may be more potent

95
Q

Pharmacologically, what is the definition of a receptor?

A

any macromolecule in a cell to which a drug binds to produce its effects

96
Q

What’s the relationship between selectivity and side effects?

A

The more selective a drug, the fewer side effects

97
Q

Describe Simple Occupancy Theory

A
  1. The intensity of response to a drug is proportional to the number of receptors occupied by that drug
  2. Maximal response occurs when all available receptors have been occupied
98
Q

What are some shortcomings with the simple occupancy theory?

A

According to the theory, two drugs that act on the same receptor should produce the same maximal effect, but they don’t

one drug can have higher maximal efficacy than another, even though they target the same receptor

99
Q

Modified Occupancy Theory ascribes two qualities to drugs:

A
  1. Affinity (strength of attraction between a drug and its receptor - potency)
  2. Intrinsic Activity (ability of a drug to activate a receptor upon binding - maximal efficacy)
100
Q

When drugs bind to receptors, they can do one of two things:

A
  1. mimic the action of endogenous regulatory molecules
  2. block the action of endogenous regulatory molecules
101
Q

What are agonists?

A

Drugs that mimic the actions of endogenous regulators

102
Q

What are antagonists?

A

Drugs that block the actions of endogenous regulators

103
Q

What are partial agonists?

A

mimic actions of endogenous regulatory molecules, but produce weaker responses

104
Q

Agonists are molecules that ______

A

activate receptors

105
Q

Antagonists produce their effects by:

A

preventing receptor activation

106
Q

How do antagonists effect receptor function?

A

They pretty much don’t

They just stop it from being activated. If activated, it will still function just the same

107
Q

If you give an antagonist but there is no agonist present, what will happen?

A

Absolutely nothing

If the receptor isn’t being activated by an agonist, the blocking effect won’t have any consequences

If you gave someone narcan who wasn’t actively high, nothing would happen

108
Q

Are most antagonists competitive or noncompetitive?

A

competitive

109
Q

What’s another word for non-competitive antagonists?

A

Insurmountable

110
Q

If a non-competitive antagonist is given and binds to a receptor, why does the dose still have limited effect?

A

Cells are constantly breaking down and replacing receptors. That drug’s decreasing effectiveness will depend on the break down of the receptors, not the breakdown of plasma levels

111
Q

What is unique about partial agonists?

A

They can act as antagonists and agonists

ex: pentazocine and meperidine (when pentazocine is given alone, it acts as an agonist on opioid receptors and produces mild pain relief. If given with meperidine, it antagonizes the binding of meperidine and prevents it from exert its greater intrinsic activity)

112
Q

What are some drugs that don’t interact with receptors?

A

Antacids, antiseptics, saline laxatives, chelating agents

All of these work through simple physical or chemical interactions and don’t involve any kind of cellular receptor

113
Q

What is the ED50?

A

average effective dose

Dose required to produce a defined therapeutic response in 50% of the population

114
Q

What is LD50?

A

Lethal dose in 50% of the population

115
Q

What is the therapeutic index?

A

A measure of the drug’s safety

ratio of the drug’s LD50 to its ED50

A large therapeutic index = relatively safe

Small therapeutic index = relatively unsafe

116
Q

In order for a drug to be truly safe, what must be true?

A

the highest dose required to produce therapeutic effects must be substantially lower than the lowest dose required to produce death

117
Q

When two drugs interact, there are three possible outcomes:

A
  1. Intensification (either increased therapeutic or adverse effects)
  2. Reduction (either reduced therapeutic or reduced adverse effects)
  3. Creation of a Unique Response (effects that do not occur when one or the other is used alone)
118
Q

Drugs interact through four mechanisms:

A
  1. Direct chemical or physical interactions (IV compatibility)
  2. Pharmacokinetic Interactions (altered absorption, distribution, protein binding, pH etc)
  3. Pharmacodynamic Interactions (effecting the same receptor)
  4. Combined Toxicity
119
Q

Why does giving bicarb help with aspirin toxicity?

A

when the extracellular space becomes more basic, acidic drugs (such as aspirin) are drawn from within the cells and into the extracellular space. Once there, they are ionized and trapped from re-entering the cell

120
Q

Some drugs increase the metabolism of other drugs, and others decrease the metabolism of other drugs. How?

A

Inducing synthesis or inhibiting drug-metabolizing enzymes (primarily P450 enzymes)

121
Q

What is the primary function of PGP?

A

transporting a wide variety of drugs OUT OF CELLS

122
Q

Most of the drugs that induce P450 have what effect on PGP?

A

Usually the same. Drugs that induce or inhibit P450 have the same effect on PGP

123
Q

What effect on other drugs would a PCP inducing drug have?

A

Reduced Absorption

Reduced Fetal Drug Exposure

Reduced brain drug exposure

Increased drug elimination

124
Q

Grapefruit raises drug levels mainly by inhibiting:

A

intestinal CYP3A4 metabolism of many drugs

125
Q

Grapefruit pretty much never affects IV medications. Why?

A

Because it only effects intestinal CYP3A, almost never in the liver

126
Q

Patients taking MAOIs MUST avoid foods that contain:

A

tyrosine (aged cheese, yeast extracts, Chianti)

127
Q

Most drug-food interactions concern drug _____ or drug ____ and very rarely drug _____

A

absorption or metabolism

action

128
Q

What is an example of a food that cause decreased drug action?

A

Leafy greens (high in Vit K) and coumadin

Pharmacology I (29 decks)

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