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A - NAPLEX > Chapter 78: Pharmacokinetics > Flashcards

Chapter 78: Pharmacokinetics Flashcards

1
Q

____ is what the human body does to a drug

A

Pharmacokinetics

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2
Q

____ is what the drug does to the human body

A

Pharmacydynamics

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3
Q

Pharmacokinetics involves the study of drug ___, ___, ___ & ____

A

Absorption
Distribution
Metabolism
Excretion

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4
Q

Absorption is not required when a drug is given ___

A

intravascularly

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5
Q

Some drugs are extensively metabolized in the liver before reaching the systemic circulation; this is called

A

first-pass metabolism

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6
Q

Some drugs are transported through the bile back to the gut where they can be reabsorbed; this is called

A

enterohepatic recycling

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7
Q

Passive diffusion is movement of drugs from an area of ___ concentration to an area of ___ concentration

A

High; low

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8
Q

Active transport occur when:

A

drugs are moved across the gut wall via transporter proteins

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9
Q

How does drug absorption occur with oral drugs

A

stomach –> small intestine –> liver –> systemic circulation

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10
Q

What is drug disintegration

A

When a solid oral dosage form is ingested and breaks into smaller pieces in the GI tract

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11
Q

What is drug dissolution

A

When the smaller pieces of ingested drug are broken down and dissolve, releasing the active ingredient

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12
Q

Which drug formulations generally have fast absorption

A

SL and ODT

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13
Q

Rank the rate of absorption of the following formulations from fastest to slowest:

  • IR
  • ER
  • IV
  • ODT
  • SL
A

IV > SL > ODT > IR > ER

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14
Q

Most IR drug formulations dissolve and get absorbed rapidly, but some can be destroyed in the gut, primarily through which chemical process

A

hydrolysis

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15
Q

Which drug formulation can limit drug degradation in the stomach (acidic) but permits dissolution in the intestine (basic)

A

Enteric-coated

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16
Q

If a drug has poor absorption, once of the methods used to increase the dissolution rate is to

A

reduce particle diameter, which increases surface area

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17
Q

Drugs with very small particle diameters are referred to as

A

micronized

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18
Q

The rate of dissolution is described by which equation

A

Noyes-Whitney

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19
Q

The rate and extent to which a drug dissolves depends on the drug’s ___

A

solubility

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20
Q

As a drug moves through the GI tract, only ___ drug is absorbed into the bloodstream

A

dissolved

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21
Q

What is bioavailability

A

The extent to which a drug is absorbed into the systemic circulation or the % of drug absorbed from extravascular (e.g., oral) relative to intravascular administration (e.g., IV)

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22
Q

A drug with good absorption has high bioavailability ( > __%)

A

70

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23
Q

A drug with poor absorption has low bioavailability ( < __%)

A

10

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24
Q

Which two antibiotics have high bioavailability

A

Levofloaxacin and linezolid

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25
Q

T/F: the oral and IV doses of Levofloaxacin and linezolid are the same and nearly 100% of the oral dose is absorbed

A

True

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26
Q

When drugs are converted from IV to PO in the same dose by protocol, it is called

A

Therapeutic interchange

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27
Q

Bioavailability can be calculated using AUC (the total exposure of drug following administration). What is the equation

A

F (%) = 100 x (extravascular AUC/IV AUC) x (IV dose/ extravascular doe)

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28
Q

What is the formula to calculate an equivalent dose of a drug when the dosage form is changed

A

Dose of new dosage form = Amount Absorbed from Current Dosage Form / F of new dosage form

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29
Q

What is drug distribution

A

drug molecules move from systemic circulation to the various tissues and organs of the body

30
Q

Factors that favor passage across membranes and greater drug distribution to the tissues:

A
  • high lipophilicity
  • low molecular weight
  • unionized
  • low protein binding
31
Q

The primary protein responsible for drug binding

A

albumin

32
Q

Only the ___ form of a drug can interact with receptors, exert therapeutic or toxic effects & be cleared from the body

A

unbound (free)

33
Q

If a drug is highly protein bound & ____ is low, then a higher percentage of the drug will be in the unbound form

A

serum albumin

34
Q

Free phenytoin and ionized calcium only measure the ____ portion, so no adjustment is required for hypoalbuminuria

A

unbound

35
Q

Correction formulas for calcium and phenytoin allow us to determine what the concentration would be if _____

A

albumin was normal

36
Q

With hypoalbuminemia, the corrected level of a highly protein bound drug will be ___ than the total level reported by the lab

A

higher

37
Q

Corrected calcium formula

A

Ca corrected (mg/dL) = calcium (serum) + [(4 - albumin) x (0.8)]

38
Q

Corrected phenytoin formula

A

Phenytoin corrected (mcg/mL) = total phenytoin measured / (0.2 x albumin) + 0.1

39
Q

What is Vd

A

how large an area in the patient’s body the drug has distributed into

40
Q

Vd formula

A

Vd = amount of drug in body/concentration of drug in plasma

41
Q

What is metabolism of a drug

A

when it is converted from its original chemical structure into other forms to facilitate elimination from the body

42
Q

What are the primary sites for drug metabolism

A

the gut and liver

43
Q

Enzyme metabolism involves

A

Phase I reactions (oxidation, reduction, hydrolysis) & phase II reactions (conjugation)

44
Q

What is excretion

A

irreversible removal of drugs from the body

45
Q

How can you increase excretion of a weak base

A

acidifying the urine

46
Q

How can you increase excretion of a weak acid

A

alkalinizing the urine

47
Q

What is clearance

A

the rate of drug removal in a certain volume of plasma over a certain amount of time (the efficiency of drug removal from the body)

48
Q

Most drug elimination occurs at a

A

steady state (called the rate of elimination)

49
Q

Clearance formula

A

Cl = rate of elimination (mg/hr) / concentration (mg/L)

50
Q

What is the most reliable measurement of a drug’s bioavailability

A

AUC

51
Q

Formula for the clearance for extravascular administration

A

Cl = F x Dose/AUC

52
Q

Formula for the clearance for IV administration

A

Cl = Dose/AUC

53
Q

What is first-order elimination or first-order kinetics

A

A constant PERCENTAGE of drug is removed per unit of time (e.g., a 325 mg dose of APAP is eliminated at the same rate as a 650 mg dose)

54
Q

What is zero-order elimination or zero-order kinetics

A

A constant AMOUNT of drug (mg) is removed per unit of time, no matter how much drug is in the body

55
Q

Which drugs exhibit Michaelis-Menten kinetics (aka saturable, or non-linear kinetics) & what can happen if the doses of these drugs are doubled

A

Phenytoin, theophylline, and voriconazole

-Doubling the dose of these drugs can double the serum concentration

56
Q

Michaelis-Menten kinetics:

At very low concentrations (much less than the Km), the rate of metabolism mimics a ____ process

A

first-order

57
Q

Michaelis-Menten kinetics:

At most concentrations approaching and exceeding the Km, the rate of metabolism becomes ___

A

mixed

58
Q

Michaelis-Menten kinetics:

At even higher concentrations relative to Km, the rate of metabolism approaches ___ order (e.g., Vmax)

A

zero

59
Q

Most drugs follow _____ kinetics

A

first-order (linear)

60
Q

In first-order kinetics, at steady state, doubling the dose approximately ___ the serum concentration

A

doubles

61
Q

What is the elimination rate constant (ke)

A

Fraction of the drug that is cleared per unit of time

62
Q

Ke formula

A

Ke = Cl/Vd

63
Q

How would you interpret a ke that is 0.1 h-1

A

10% of the drug remaining is cleared per hour

64
Q

The ke can be used to predict the concentration of a drug at any time after the dose. What is the calculation

A 
C2 = C1 x e^-kt
ke = ln (C1/C2)/t
65
Q

What is the elimination half-life

A

The time required for the drug concentration to decrease by 50%

66
Q

Formula for half-life

A

t1/2 = 0.693/ke

67
Q

How many half-lives does it take for a drug to reach steady state

A

~5

68
Q

__ half-lives are required to eliminate more than 95% of the drug

A

5

69
Q

What is steady state

A

when the rate of drug intake = the rate of drug elimination

70
Q

Loading dose formula

A

LD = Desired concentration x Vd / F

71
Q

What is a peak level

A

the highest concentration in the blood the drug will reach

72
Q

What is a trough level and when is it drawn

A

the lowest concentration the drug will reach in the blood

It is drawn just before the next dose

A - NAPLEX (83 decks)

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