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PHPY 304 > Pharmacokinetics, drug interactions > Flashcards

Pharmacokinetics, drug interactions Flashcards

1
Q

________ - produces pharmacological action

A

free drug

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2
Q

drug bound to plasma protein is most likely ________

A

inactive

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3
Q

Displacement of a drug from plasma protein binding generaly causes ….

A

no change in its overall effect or adverse effects

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4
Q

Most drug is extravascular, so a change in free plasma drug concentration caused by displacement from plasma protein binding would be ______

A

minimal

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5
Q

Most drug is intravascular, so a change in free plasma drug concentration caused by displacement from plasma protein binding would have _________

A

significant effects

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6
Q

After absorption a drug is …

A

distributed to various body compartments

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7
Q

Distribution

A

the REVERSIBLE movement of a drug between body compartments

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8
Q

Factors that affect distribution from the general circulation to other tissue compartments are:

(4) ICBP

A

Ionization

Capillary permeability

Blood Flow

Plasma protein binding

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9
Q

Capillary Permeability:

In the _____, ______, and ______, the capillaries are very leaky.

A

kidney, liver and spleen

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10
Q

Capillary Permeability:

what do drugs doregardless of whether they are poorly lipid soluble, charged, or polar?

A

drugs leave the capillaries regardless

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11
Q

Blood Brain Barrier

Brain capillaries have __________

A

tight junctions

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12
Q

Blood-Brain Barrier

Only __________ drugs diffuse across brain capillaries

(unless other drugs are actively transported across)

A

lipophilic drugs

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13
Q

__________ exist between endothelial cells in the brain capillary

A

tight junction

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14
Q

Blood Brain Barrier

Clinical implication:

The degree to which drugs penetrate the ____ should be known to treat diseases of the nervous system properly.

A

brain

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15
Q

Blood Brain Barrier

Clinical implication:

The amine _______ (to treat Parkinson’s disease), has to be administered in the form of its precursor because it can’t cross the blood-brain barrier.

A

Dopamine

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16
Q

Dopamine’s precursor can be used to treat what disease of the central nervous system?

A

Parkinson’s disease

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17
Q

What is the precursor of dopamine? Why can’t it cross the Blood brain barrier?

A

L-dopa

because its metabolized by enzyems in the BBB

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18
Q

Blood Brain Barrier

Clinical implication:

The Blood brain barrier does not work properly in ares of ______ or _____

A

infection or injury

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19
Q

Blood Brain Barrier

Clinical implication:

______ of the brain develop new blood vessels and capillaries that have NO tight junctions.

A

Tumors

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20
Q

Blood Brain Barrier

Clinical implication:

substances such as _____________________ penetrate normal brain tissue very slowly, but they enter tumor tissue easily to help in diagnosis.

A

radioactive iodine-labeled albumin

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21
Q

Blood flow:

The tissue that receives more ______ receives more _____.

A

drug, blood

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22
Q

Blood flow:

____, _____, _____ receive more blood flow than

skeletal muscle. Whereas fat and _____ receive little blood flow.

A

Brain, liver, kidneys

skin

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23
Q

Total Body Water = ___% of body weight ~ ___ L.

___ of TBW in intracellular fluid space ~ ___ L.

___ of TBW in extracellular fluid space ~ ___ L.

___ of extracellular fluid is intravasuclar (i.e. plasma)

Adult blood volume ~ ___ L.

A

60% , 42L

2/3 , 28L

1/3 , 12L

1/3

5L

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24
Q

When we administer a drug, it distributes into many compartments - aka _________

A

volume of distribution (Vd)

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25
Q

______ - can be defined as a theoretical or apparent volume in which the total amount of administered drug should be uniformly distributed to account for its plasma or blood concentration.

A

Volume of distribution.

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26
Q

What is the formula for Volume of distribution (Vd) ?

A

Vd = dose administered / Plasma concentration

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27
Q

A high Vd indicates…..

A

that most of the drug is in the extravascular compartment (eg. amiodarone)

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28
Q

Volume of distibution - clinical significance

If the plasma concentration of a drug is high (eg due to high plasma protein binding) its Vd will be ___

A

low

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29
Q

Volume of distibution - clinical significance

A low Vd indicates taht…

A

most of the drug is in the vascular compartment (eg. bound to plasma proteins, a drug such as warfarin).

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30
Q

Redistribution of Drugs

Initially - what happens to organs like the brain and kidney when a drug is intravenously administered?

A

the brain and kidney receive greater percent or fraction of cardiac output and majority of the intravenously administered drug.

show profound drug effect.

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31
Q

Redistribution of Drugs

Initially - What happens to organs such as adipose tissue and skin after intravenous administration of drug?

A

organs like the adipose tissue and skin receive much less blood flow and very little drug.

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32
Q

Redistribution of Drugs

After time - what happens to adipose tissue after drug administration?

A

adipose tissue accumulate drug due to high storage capacity.

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33
Q

Redistribution of Drugs

While adipose tissue accumulates drug due to storage capacity , what happens to plasma concentration of the drug?

A

it falls

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34
Q

Redistribution of Drugs

As the drug is redistrubuted to major storage tissues, What happens to organs such as the brain and kidney?

A

drug is quickly removed from organs lke the brain and kidney to equilibriate with low plasma concentration

drug effect quickly wears off in brain and kidney

***EG. I.V. thiopental to induce anesthesia.

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35
Q

Redistribution of Drugs

Parenteral anesthetics such as ___________ (a lipid barbiturate drug) are used to induce anaesthesia.

A

intravenous thiopental

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36
Q

Redistribution of Drugs

Induction from anaesthesia is ______ (fast or slow)

Recovery from anaesthesia is ______ (fast or slow)

a ______ (higher/lower) concentration is given to take advantage of _______

If we use the regular concentration of thiopental what will happen?

A

fast or rapid

fast or rapid

lower , redistribution

then anesthesia and recovery will be prolonged over many hours, there will be little redistribution.

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37
Q

Biotransformation (Drug Metabolism)

The main purpose of drug metabiolsim is…

A

chemical modification of drugs by enzymes, to make them MORE POLAR (less lipid soluble) , and therefore readily excretable by the kidneys.

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38
Q

Biotransformation (Drug Metabolism)

Drug metabolizing enzymes are present in:

*L

*G

*L

K

S

B

B

A

The liver

Gastrointestinal Wall

Lungs

Kidneys

Skin

Blood

Brain

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39
Q

Biotransformation (Drug Metabolism)

Certain drugs do not reach their site of action because of ___________.

EG. a drug can be destroyed by digestive enzymes.

What would be useful in such cases?

A

pharmacokinetic obstacles

Their precursors, known as prodrugs, may be useful in such cases.

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40
Q

Biotransformation (Drug Metabolism)

____ are inactive when administered. What can cause them to be converted to active form?

A

Prodrugs

After metabolism they are converted to active form

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41
Q

Biotransformation (Drug Metabolism)

Examples of Prodrugs:

_______________ - omeprazole, Iansoprazole are prodrugs.

What are they used for?

A

Proton - pump inhibitors

reduce stomach acid secretion.

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42
Q

Biotransformation (Drug Metabolism)

Examples of prodrugs:

what are 2 examples of proton-pump inhibitors?

What prodrug is convereted into Active compound dopamine to treat parkinson’s disease?

A

omeprazole, iansoprazole

Levo-dopa or L-dopa

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43
Q

Two-Phase Biotransformation

Phase I _________ reactions

Phase 2 ______ reactions

A

Functionalization

conjugation

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44
Q

Two-Phase Biotransformation

Oxidation, reduction, and hydrolytic reactions have what effect on the drug?

What Phase of biotransformation is this?

A

makes the drug more polar but not necessarily inactive

Phase I functionalization reaction

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45
Q

Two-Phase Biotransformation

Phase I includes what types of reactions?

A

oxidation, reduction and hydrolytic reactions

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46
Q

Two-Phase Biotransformation

Conjugation to polar groups: glucuronidiation, sulfation, acetylation has what effect on the drug?

What phase of biotransformation is this?

A

must of these result in drug inactivation

Phase II conjugation reactions

47
Q

Two-Phase Biotransformation

Phase I Enzymes:

Microsomal cytochrome ___ belongs to what family of enzymes?

  • they transfer electrons from ______ to an oxygen molecule and thus ______ drugs. (mostly hydroxylations, and dealkylations).
A

P450 , monooxygenase family of enzymes.

NADPH, oxidize

48
Q

Two-Phase Biotransformation

Phase I Enzymes:

Microsomal cytochrome P450:

these enzymes act on structurally unrelated drugs which means they are ….

they are located in the ________ of the cell.

they require _____ and ___

Metabolize the ____ (shortest, widest) range of drugs

In most cases these reactions _____ (activate or inactivate) the drug.

A

not very substrate specific

endoplasmic reticulum

NADPH O2

widest

inactivate

49
Q

Two-Phase Biotransformation

Phase I Enzymes:

Over ___ % of drug oxidation by cytochrome enzymes can be attributed to 6 main CYPs:

What are they?

ACCDEA

A

90%

CYP1A2

CYP2C19

CYP2C9

CYP2D6

CYP2E1

CYP3A4

50
Q

Two-Phase Biotransformation

Phase I Enzymes:

_____ is the primary enzyme for metabolism of about _____ of all drugs and is inhibited or induced by many drugs.

This can cause ___________

A

CYP3A4

Half or 50%

can cause drug-drug interactions (DDI)

51
Q

Two-Phase Biotransformation

Phase I Enzymes:

What are the top 3 relative proportions of drugs metabolized by CYPs:

A

CYP3A4 - largest 50%

CYP2D6 ~ 18%

CYP2C9 ~ 18%

52
Q

Factors affecting drug biotransformation:

What are the 2 factors of biotransformation?

A

enzyme induction and inhibition

53
Q

Two-Phase Biotransformation

Drugs (including herbals) and other substances (foods) can _____ or ____ the expression of some metabolizing enzymes, especially the ________ enzymes.

This can possible cause the creationg of more enzyme.

A

stimulate or inhibit

cytochorome P450 enzymes.

54
Q

Two-Phase Biotransformation

Significance of Phase I drug metabolizing enzymes:

Induction or inhibition of phase I enzymes (CYT P450) can cause ____________ when two or more drugs that are metabolized by the same ____ are given.

______ is the primary enzyme for metabolism of about half of all drugs and is inhibited or induced by many drugs and is involved in many drug drug interactions.

A

drug-drug interactions DDI

enzyme

CTP3A4

55
Q

Two-Phase Biotransformation

Induction of enzyme and drug interactions:

Inducers cause … _________________.

What can cause treatment failure?

Examples include:

R

B

*S

A

expression of more CYP enzymes and faster elimination of substrate drugs.

Lower than expected drug levels can cause treatment failure

Rifampin (antibiotic)

Barbiturates

*St John Wort (herbal antidepressant)

56
Q

Two-Phase Biotransformation

Inhibitors can … ________________.

Higher than expected drug levels can cause ______.

Examples:

*G

*C

E

I

A

inhibit the activity of CYP enzymes and reduce elimination of substrate drugs.

drug toxicity

*Grapefruit juice

*Cimetridine (stomach acid inhibitor)

Erythromycin (antibiotic)

Itraconazole (antifungal)

57
Q

Two-Phase Biotransformation

What is CYP Polymorphism?

The most common P450 polymorphism in Caucasians is ______ expression.

around 10% of Cucasians lack expression of this enyzme.

around 5% of ____ lack expression of this enzyme.

A

Genetic variations in the population - mutations are foundi n some drug metabolizing enyzmes in some people.

CYP2D6

Africans

58
Q

_____ is almost ineffective as an analgesic in some patients. This drug must be metabolized by ______ to morphine for analgesic effect.

A

Codeine

CYP2D6

59
Q

Two-Phase Biotransformation:

Phase II reactions:

In these reactions a chemical group such as

GA

S

G

AA

A

are added to the drug.

A

Glucuronic Acid

Sulfate

Glutathione

amino acids

acetate

60
Q

Two-Phase Biotransformation:

Phase II reactions:

The conjugated drug is ___________ and in most cases inactive.

The conjugated drug is ______ (rapidly/slowly) excreted.

Enzymes for Phase II reactions are mostly located where?

A

highly polar

rapidly

cell cytosol

61
Q

Two-Phase Biotransformation:

Phase II reactions: (clinical significance)

___% of Americans and

__-__% of Eurpoeans have reduced expression of ______ enzyme.

What does this enzyme do?

A

50%

60-70%

Acetylating enzyme (N-acetyl transferase or NAT - “slow acetylators”)

they slowly metabolize drugs such as Isoniazid (antituberculosis drug), procainamide (anti-arrythmic drug) and caffine.

62
Q

Drug interactions can be easily avoided in most cases

T or F?

A

True

63
Q

Drug interactions are defined as a situation in which…

What are the 3 possible outcomes?

A

a substance affects the activity of a drug.

  1. Increased effect, toxicity
  2. Decreased effect, treatment failure
  3. New effect. (rare)
64
Q

Drug interactions cause up to ___% of hospital admissions.

>__% use > 1 drug/week

>__% use > 5 different drugs/week

12% use > __ different drugs/week

A

2.8%

90%

40%

10

65
Q

Which sex takes more drugs, men or women? In particular, what type of drugs do they take?

A

women

psychoactive, arthritis drugs

66
Q

Drug use is greatest among what 3 groups of people?

F

H

N

A

frail elderly

Hospital patients

nursing home residents

  • typically a nursing home resident is given 7-8 drugs on a regular basis.
67
Q

The interaction between two drugs is called - _____

between a drug and a food item is called - ______

between a drug and herbs is called - ______

A

drug-drug interactions (DDI)

Drug-food interactions

Drug-herb interactions

68
Q

Types of Drug-Drug Interactions:

____________ - two drugs affecting the same system (effect on the organism) e.g Two sedative drugs will produce more sedation.

A

Pharmacodynamic Interaction

69
Q

Types of Drug-Drug Interactions:

__________ - One drug changes the absorpion, distribution, metabolism, excretion (ADME) of another.

A

Pharmacokinetic Interaction

70
Q

What changes in a pharmacokinetic interaction?

ADME

A

absorption

distribution

metabolism

excretion

71
Q

Drug-Drug Interaction - Examples:

Absorption:

Antacids reduce absorption of _______ (antibiotic)

calcium supplements reduce absorption of _______ (hormone)

A

tetracycline

thyroxine

72
Q

Drug-Drug Interaction - Examples:

Distribution:

Competition for plasma protein binding by ________ (N-SAIDs) and ______ (anticoagulant).

Is Plasma protein binding specific or non specific?

A

non steroidal anti-inflammatory drugs (N-SAIDS)

warfarin (anticoagulant)

nonspecific

73
Q

Drug-Drug Interaction - Examples:

Excretion:

_______ reduces exretion of penicillin by competition for the ____________.

Which of the 2 drugs is used to treat Gout by reducing reabsorption of uric acid?

A

Probenecid

kidney tubule transport system

Probenecid

74
Q

Drug-Drug Interaction - Examples:

Metabolism:

Two drugs metabolized by the same enzyme can compete for the enzyme. (eg. _______)

A

CYP3A4

75
Q

Drug-Drug Interaction - Examples:

What is the most common reason for drug-drug interactions?

A

Metabolism - one drug affecting the metabolism of another drug.

76
Q

What drug is very notorious in terms of drug-drug interactions (DDIs)?

A

Warfarin

77
Q

What are the five major mechanisms and examples of drug interactions with warfarin?

P

Ga

Gu

Wm

I

A

Altered platelet function

Direct gastrointestinal injury

Altered gut vitamin K synthesis

Altered warfarin metabolism

Interference with Vitamin K cycle

78
Q

Warfarin DDI:

an example of :

altered platelet function is…

Direct gastrointestinal injury is…

Altered gut vitamin K synthesis is…

Altered warfarin metabolism is…

Interference with vitamin K cycle is…

A

acetylsalicylic acid, clopidogrel

nonsteroidal anti-inflammatory drugs

antibiotics

co-trimoxazole, metronidazole, fluconazole, amiodarone

acetaminophen

79
Q

NSAIDs and warfarin interaction

An NSAID greatly increases risk of warfarin ______ because of multiple interactions:

A

Toxicity

80
Q

NSAIDs and warfarin interaction

4 reactions that increase the risk of warfarin toxicity due to NSAIDs:

  1. Protein bound warfarin is ______ by NSAID - what does this cause?
  2. Nsaids_________________ (anticlotting action) that adds to anticoagulant action of warfarin
  3. Some NSAIDs prevent ______________________ by competition for the metabolizing enzyme. This causes what?
  4. NSAIDs directly cause gastric injury and warfarin _____________.
A
  1. displaced, increase in free plasma warfarin and causes toxicity
  2. supress platelet function
  3. metabolism of warfarin , increase in plasma warfarin and toxicity
  4. can cause gastric bleeding.
81
Q

What are the 4 reactions that result from Warfarin NSAIDs interactions?

A

protein bound warfarin is displaced and increase free warfarin and toxicity

NSAIDs supress platelet function increasing the anticoagulant function of warfarin

Some NSAIDs prevent metabolism of warfarin by competition for the metabolizing enzyme - which increases warfarin and toxicity

NSAIDs directly cause gastric injury and warfarin can cause gastric bleeding.

82
Q

Drug metabolism Interactions

When should the possibility of drug interactions resulting from metabolism be considered?

A

when a patient is taking 2 or more drugs

83
Q

Drug metabolism interactions:

When should interactions with food items or herbal medicines be considered?

A

When a patient is taking a single drug metabolized by Cytochrome P450 enzymes

84
Q

Drug metabolism Interactions

When should genetic variation of metabolizing enzymes be considered?

A

in cases of drug toxicity or treatment failure.

85
Q

DDI Summary:

What out for DDIs in:

1.

2.

4.

A

the elderly

receiving more than 2 drugs

receiving warfarin, NSAIDs, antiplatelets, statins, thyroxine, statins, thyroxine

New signs/ symptoms after starting a new drug - investigate for DDI or ADR(adverse drug reaction)

86
Q

ADR stands for?

A

adverse drug reaction

87
Q

P-glycoprotein is a(n) _________.

What does it do?

Whats it’s specificity ?

Where is it located?

A

efflux pump (in to out)

uses energy (ATP) it removes compounds from inside to the outside .

has a broad substrate specificity for drugs - digoxin, quinidine, and others.

Many sites (luminal surfaces) :

  1. colon, small intestines
  2. kidney tubules
  3. brain
  4. liver- bile canaliculi
  5. Placenta
  6. cancer tissue (lots located here)
88
Q

digoxin does what?

A

increases contraction and can lead to heart failure. Very toxic

89
Q

P-glycoprotein expression is increased or incduced by what 2 drugs?

It is inhibited by what 4 types of drugs?

A

St. John’s Wort, Rifampin

verapamil, quinidine, macrolide antibiotics (erythromyacin) , antifungals

90
Q

P-glycoprotein in the blood brain barrier do what?

What mechanism is used?

A

protects the central nervous system (CNS) from a variety of structurally diverse compounds .

done through its efflux mechanisms

91
Q

P-glycoprotein plays a clinical role in drug resistance to ____________.

P-glycoprotein is over expressed in ________.

after exposure to anticancer agents , and it pumps out the _____________.

A

cancer chemotherapeutic agents

tumor cells (eg. actue myelogenous leukemia)

anticancer drugs

92
Q

drugs such as calcium channel blockers, __________ and _________ inhibit P-glycoprotein and may be useful to reverse resistance .

A

phenothiazines and cyclosporin A

93
Q

Enterohepatic recirculation

Entero —> ______

Hepatic —> ______

a compound is conjugated in the _____, excreted in the ______, deconjugated in the _______ (by bacterial enzymes) and is reabsorbed into the circulation.

A

Gi Tract

Hepatic

liver, bile, intestine

94
Q

What phenomenon prolongs the duration of action (half-life) of a drug?

A

Enterohepatic recirculation

95
Q

Enteroheatic Recycling :

Bile acids are conjugated in the ____ to ______ and ____ and excreted in the intestine where they are ________.

What percent of bile salts are reabsorbed and used in cholesterol synthesis?

A

liver, taurine, glycine, deconjugated

95%

96
Q

If we give a bile acid biding resin such as __________ or _________ we interrupt the enteropeatic recycling of bile salts and does what to cholesterol synthesis and plasma levels?

A

cholestyramine or metamucil

reduce cholesterol synthesis and plasma levels.

97
Q

Entero-Hepatic Recirculation - clinical significance

Oral contraceptive failure when ___________.

____________ is excreted via bile duct and is eliminated by bacteria in the intestines producing _____. This interrupts enterohepatic cycling.

A

antibiotic is taken.

Estrogen glucuronide , Estrogen.

98
Q

An ______ such as rifampin also induced ____ enzymes that metabolize the contraceptive hormones and thus reduces their effectiveness.

A

antibiotic

CYP enzymes

99
Q

_______ is the volume of blood from which a drug is irreversibly removed per unit of time.

Whats the units?

A

Clearance

ml / min (/kg)

100
Q

What are clearance values useful for ?

Rate of administration (maintenance dose) = ________

Whole body (systemic) clearance of a drug is…..

A

calculate maintenance dose of drug.

i.e. the dose that will allow us to maintain as steady-state concentration of a drug in the plasma

Rate of Elimination.

sum of clearance of that drug by all organs. (liver, kidney, lungs ect.)

Systemic clearance = clearanceliver + clearancekidney …

101
Q

Renal Clearance:

______ is a passive process. The kidney does not filter what kind of drug?

What kind of drug is filtered at the glomerulus?

A

Filtration

protein bound drugs aren’t filtered

free drug is filtered

102
Q

Renal Clearance

Some drugs:

_______ (low pKa) and _______ (high pKa) are secreted where?

Is this process active or passive?

A

strong acids

strong bases

mainly secreted in the proximal tubule.

Active process with separate transporters for anions and cations.

103
Q

Renal Clearance:

Unless the drug is _______, some of it is going to be reabsorbed.

A

very polar

104
Q

Renal clearance:

What is the net removal formula?

Filtration of free drug takes place where?

Where does secretion and reabsorption take place?

A

Net removal = filtered + secreted - reabsorbed

Glomerular capillaries

Vessels surrouning the tubules.

105
Q

What 3 processes in the kidney help remove drugs from the body?

A

Filtration

Secretion

Reabsorption.

106
Q

Drug Elimination Kinetics

Most drugs are eliminated according to a _______________.

A _____________ of drug is eliminated per unit of time.

Rate of elimination is proportional to what?

Blood concentration declines in a(n) ________ over time ie decreases at a rate that is proportional to its current value.

A

First order rate process

Constant fraction

proportional to the plasma concentration

exponential fashion.

107
Q

Define First -order rate of elimination.

When 40 molecules of drug is distributed evenly throughout 5 compartments, how many molecules will reach the enzyme in the liver after equilibrium?

A

a constant fraction of drug is eliminated per unit of time.

40 x 1/5th = 8 molecules in the liver

108
Q

Zero-order Elimination

Define Zero-order:

A

a constant amount of drug is eliminated per unit of time because that is the maxiumum rate of elimination when the pathway for elimination is saturated.

109
Q

Zero-Order Elimination

this metabolic mechanism for most d rugs will be saturated when?

are the doses for this rate process commonly used in therapeutics?

A

at very high concentrations

No

110
Q

Zero-order Elimination

The metabolic capacity for very few drugs becomes saturated at concentrations within the _________:

What are some examples?

A

therapeutic range

eg. phenyton, asperin (acetylsalicylic acid -ASA) , carbamazepine, ethanol

111
Q

Half-life and its clinical significance

Define Half-life:

Half life applies to drugs that are eliminated by what processing rate?

For practical purposed it takes about _ half-lives for more than 90% of a drug to be effectively eliminated from the body.

A

the time required for the blood(or plasma) concentration of a drug to be reduced by 50%

first order rate of elimination

5

112
Q

Half-life and its clinical significance

What is required for a drug to achieve steady-state concentrations in the plasma?

Steady concentration is defined as?

Example Q: If the half-life of a drug is 20 hours, then it will reach steady concentrations after what amount of time?

A

a fixed dose given at fixed intervals, its takes 5 half-lives for that drug to reach steady-state concentrations in the plasma.

where high elimination rate equals the administration rate.

5x20 = 100 hours.

113
Q

Time to steady-state or elimination is indpendent of ______.

Time required to reach steady state depends on ________ rate.

How many half lives are requried to reach 97% of steady state?

How many half lives are required to eliminate 97% of drug?

A

dosage

elimination rate

5

5

PHPY 304 (6 decks)

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