Therapeutic Drug Monitoring

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Medicine

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39 Terms

1
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what types of drugs require TDM

narrow therapeutic index + variable PK (inter- and intra-patient variability) + known concentration-effect relationship (efficacy and/or toxicity)

2
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T/F: therapeutic window and therapeutic index are not the same thing

true

3
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what does ED50 mean

the dose where 50% of the patients get the desired therapeutic effect

4
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what does TD50 mean

the dose where 50% of the patients get unwanted side-effects

5
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how does therapeutic window differ from therapeutic index?

concentration based and usually based on individual not populations

6
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what are some indications for TDM?

PK dose individualization, monitor compliance, monitor for drug interactions, and ensure efficacy/prevent toxicity

7
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TDM definition:

monitoring drug concentrations to ensure efficacy and minimize toxicity

8
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common drugs that require therapeutic drug monitoring

vancomycin, gentamicin/tobramycin, phenytoin, and warfarin

9
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therapeutic range for vancomycin:

trough 10-20 mcg/mL or AUC 400-600 mg*h/L

10
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therapeutic range for gentamicin/toobramycin:

peak 6-8 mcg/mL and trough 1-2 mcg/mL

11
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therapeutic range for phenytoin

random 10-20 mcg/mL

12
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therapeutic range for warfarin:

INR 2-3

13
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what is clearance

volume of plasma that is cleared of drug per unit time

14
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what is apparent volume of distribution (Vd)?

PK rate constant - NOT A PHYSIOLOGIC TERM and may be represented as a fraction of weight

15
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Ke =

Cl/Vd

16
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half-life =

0.693/ke

17
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define Cmax

highest concentration of drug in blood

18
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define half-life

time at which drug has lost half its maximum concentration

19
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define Cmin

lowest concentration of drug in blood

20
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define AUC

overall drug exposure

21
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how many half-lives to steady state?

4-5 half-lives

22
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define steady state

amount of drug into the system = amount of drug out of system

23
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what is true regarding the peak and trough concentrations at steady state?

consistent for each dose

24
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T/F: time to steady state is independent of dosage

true

25
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when is it ideal for TDM to be performed?

at steady state

26
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initial dose of vancomycin

15-20 mg/kg

27
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what value correlates with efficacy of vancomycin

AUC/MIC > 400

28
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what value correlates with toxicity (nephro) correlates with vancomycin

trough > 15 mg/L or AUC > 600

29
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what value correlates with efficacy of aminoglycosides

peak concentrations 5-10 mg/L for gentamicin/tobramycin and peak concentrations of 20-30 mg/L for amikacin

30
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what value correlates with toxicity of aminoglycosides?

concentrations greater than target trough of < 2 mg/L for genta/tobra and < 10 mg/L for amikacin

31
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what is a pearl of phenytoin TDM?

interpretation of concentration data is obscured in renal dysfunction due to alterations in protein binding, volume of distribution, and free drug available

32
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target total phenytoin concentration?

10-20 mcg/mL

33
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target free phenytoin concentrations

1-2 mcg/mL

34
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what can occur if INR is too high

bleeding side effects more likely

35
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what can occur if INR too low

blood clots more likely

36
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onset of action for warfarin

2-3 days

37
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duration of effect for warfarin

2-5 days

38
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half life of factor II:

72 hours

39
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target INR range for mechanical heart valves

2.5-3.5