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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

what is pharmacokinetics

A

the study of the time course of drug concentration in the body, usually as reflected in the plasma concentration (fate of drug in the body).

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2
Q

first order kinetics is also referred to as what

A

exponential kinetics characterized by a constant fractional change per unit time

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3
Q

first order kinetics is measured as what

A

the rate constant (Ke)

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4
Q

zero order kinetics is also referred to as what

A

saturation kinetics

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5
Q

first order kinetics is characterized by what

A

a constant amount of change per unit time

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6
Q

half-time or biological half life (t 1/2)

A

for drugs that are eliminated by first-order kinetics, the fractional change in the amount of drug in the blood is generally expressed by the half-life. Time required for 50% of the drug remaining in the body to be eliminated (or the time required for the blood concentration to decrease 50%).

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7
Q

rate constant of elimination (Ke)

A

For drugs that are eliminated by first-order kinetics, the rate constant is the fractional change per unit time (fraction/min, fraction/hour, etc)

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8
Q

rate constant of elimination (Ke) is equal to what

A

0.693 / t1/2
OR
t1/2 = 0.693/ke

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9
Q

what is clearance

A

the quantification of elimination

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10
Q

for most drugs in clinical setting, clearance is

A

constant

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11
Q

clearance represents the volume of

A

biological fluid that would have to be completely freed of drug to account for the rate of elimination (ie. the volume of body fluid processed in a given time)

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12
Q

clearance is expressed as

A

volume per unit time

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13
Q

individual organ clearances are

A

additive

ie. take renal cl, pulmonary cl etc. and add the volumes up to give you total systemic clearance

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14
Q

clearance can be calculated from what

A
  1. excretion rate/concentration

2. dose/area under the curve (AUC)

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15
Q

compartmental model of pharmacokinetics

A

uses selected model to “fit” parameters to data

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16
Q

noncompartmental model of pharmacokinetics

A

most use the same basic principles (Trapezoidal rule; observed data; calculated elimination rate constant; standard formulas for the rest)

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17
Q

Fate of a drug

A
  1. liberation
  2. absorption
  3. distribution
  4. metabolism
  5. excretion
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18
Q

what is liberation

A

release from matrix

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19
Q

what is absorption

A

process and rate

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20
Q

what is distribution

A

movement in body

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21
Q

what is metabolism

A

removal by biotransformation

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22
Q

what is excretion

A

physical removal from body

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23
Q

what are key pharmacokinetic parameters

A
  • clearance
  • volume of distribution
  • half-life
  • bioavailability
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24
Q

what is volume of distribution

A

concept for a given dose, the theoretical size necessary to produce a specific calculated exposure

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25
Q

what is half-life

A

the length of time necessary to reduce or “eliminate” 50% of the current level of drug

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26
Q

what is bioavailability

A

the fraction of the dose that reaches systemic circulation

f=1 for IV

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27
Q

assumptions of a one compartment model

A
  • the body is a single compartment with a volume (V) and drug concentration (C)
  • distribution of drug is uniform and rapid compared with absorption and elimination
  • elimination of the drug conforms to 1st order kinetics
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28
Q

see diagram: slide 10-11

A

see diagram: slide 10-11

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29
Q

assumptions of a two compartment model

A
  • the body contains 2 compartments, central and peripheral
  • all kinetics are first order
  • elimination is form the central compartment
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30
Q

see diagram: slide 12 + 13

A

see diagram: slide 12 + 13

31
Q

what are model independent parameters

A
  • clearance, half-life, Vd
  • AUC
  • Cmax (max concentration)
  • Tmax (time of max concentration)
32
Q

see calculations: slide 16

A

see calculations: slide 16

33
Q

what is the plateau principle

A
  • when a drug is administered intravenously, the plasma concentration will increase until the rate of elimination and administration are equal
  • at that point, the plasma drug [ ] will remain constant until there is a change in the dosage rate of elimination kinetics
34
Q

steady state concentration (Css) equation

A

rate of administration/total body Cl = dosing rate/Cl

35
Q

dosing rate equals

A

Cl x Css

36
Q

Css equals

A

dosing rate/Cl

37
Q

see diagram: slide 19

A

see diagram: slide 19

38
Q

time required to achieve steady state depends on

A

half life

39
Q

how many half lives does it take to achieve steady state

A

4-6 half-lives

40
Q

see diagram: slide 21

A

see diagram: slide 21

41
Q

conditions for fixed rate, multiple doses

A
  • the drug will accumulate in the body if the time interval between doses is less than 4 half lives
  • total body stores of the drug increase exponentially to a plateau
  • the plasma [ ] will fluctuate during the dosing interval
  • Css now represents the mean [ ] of the drug during the dosing interval
42
Q

for oral dosing, what will also influence Css

A

bioavailability

43
Q

what is bioavailability

A

is the fraction (f) of the administered dose that reaches the systemic circulation

44
Q

what is the equation of Css in a fixed rate, multiple dose regimen

A

Css = (f) x dose / (dosing interval x Cl)

45
Q

what happens to the [plasma] with a fixed rate multiple dose regimen

A

[plasma] will fluctuate btwn a maximum (peak) and a minimum (trough) concentration

46
Q

see diagram: slide 24

A

see diagram: slide 24

47
Q

for therapy characterized by repeated intermittent dosing, the choice of dosage interval is based on what

A
  • tolerance btwn dose variations of serum concentraions (based on half life and toxicity of the drug)
  • patient convenience plays a role for out patient therapy
48
Q

when would a loading dose be administered

A

when the time to reach steady state is needed immediately

49
Q

the amount of drug required to achieve a given steady-state value in plasma is the amount that

A

must be in the body when the desired steady-state is reached

50
Q

what variable relates the total drug [ ] in the body to the plasma [ ]

A

Vd

51
Q

loading dose equation is

A

loading dose = Css x Vd

52
Q

what is nonlinear, dose-dependent or saturable elimination kinetics

A

a capacity-limited process where drugs exceed the metabolic/excretory capacity of the body to eliminate that drug as a linear rate

53
Q

describe the clearance rate of a nonlinear elimination

A

Cl will vary with the [ ] of drug in a manner analogous to the M-M equation for enzyme kinetics

54
Q

virtually all drugs taken by pregnant women are transferred to some degree across the

A

placenta to the fetus

55
Q

delivery of single doses in pregnant women is limited by what

A

blood flow to the placenta

56
Q

when does peak fetal blood concentration occur

A

btwn 20 mins and 4 hrs after IV dosing depending on the chemical characteristics of the drug

57
Q

chronic dosing during pregnancy can lead to what

A

a steady-state

fetal:maternal [ ] approach unity

58
Q

what are 5 critical time frames of pediatric pharmacology

A
  1. conception to birth
  2. birth to 1 month
  3. 1 month to 2 yrs
  4. 2 years to 12 yrs
  5. 12 yrs to 18 yrs
59
Q

what drug characteristics affect developmental factors

A
  • drug absorption
  • drug distribution/% body water
  • drug metabolism
  • drug excretion
60
Q

dosages are determined by

A
  • formula

- body to surface area

61
Q

drug disposition and aging is determined by what

A
  • absorption
  • distribution
  • drug metabolism
62
Q

how is absorption affect by age

A

relatively normal

63
Q

how is distribution affect by age

A

aging is characterized by decreased lean body mass, increased % of body weight represented as fat, and decreased total body water

64
Q

how is drug metabolism affected by age

A

-slower on average in the elderly due to decreased hepatic blood flow and smaller liver size

65
Q

does the aging liver decreases its metabolism for all drugs

A

the aging liver to metabolize drugs does not decline in a similar way for all pharmacological agents, and the clearance of some drugs is largely unchanged (depends on intrinsic Cl)

66
Q

what is the cockroft-gault equation

A
  • estimates the glomerular filtration rate and generally

- obtained by estimating endogenous creatine clearance

67
Q

what is cockroft-gault equation

A

CreatineCl = [140-age] [weight] / (72 x serumcr in mg/dL)

68
Q

for women, creatinine clearance is –% of the value calculated by the Cockroft-Gault eqn

A

85%

69
Q

why might the GRF be overestimated using the Cockroft-Gault eqn in older individuals with low [ ]

A

bc endogenous creatinine production from muscle is decreasing with age

70
Q

how does age affect renal excretion

A

-aging is associated with decreased renal size and renal blood flow, leading to decreases in glomerular filtration rate

71
Q

decreases in tubular function parallel those in

A

glomerular function

72
Q

based on cross-sectional studies, creatinine clearance decreases an average of

A

8ml/min/decade after age 30

73
Q

what dosage adjustments are done for renal dysfunction

A
  1. decrease dose, but maintain dosage interval

2. maintain dose, but increase length of dosage intervals

74
Q

when is decreasing dose the preferred method of dosage adjustment for renal dysfunction

A

when a relatively constant plasma concentration of the drug is desired

Pharmacology (23 decks)

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