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Lab 3 > PK: therapeutic drug monitoring + DDIs > Flashcards

PK: therapeutic drug monitoring + DDIs Flashcards

1
Q

use drug conc to do what 2 things?

A

individualise treatment
adjust dosing regimen

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2
Q

when monitoring drug, looking for what 3 things?

A

clinical outcome
- symptoms improving
- infection being treated

toxicity
- is px developing any ADRs = high dose :/

drug conc over time

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3
Q

Why is therapeutic drug monitoring necessary?

A
  • identifies issues w dosing regimen: toxicity, efficacy
  • individualise treatment
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4
Q

What dosing regimen issues can be identified by monitoring?

A
  • wrong drug: within TW but still not working
  • wrong dose: on lower end of TW or below MEC, but adherence is a consideration too
  • whether toxicity is due to drug or disease progression
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5
Q

2 changes to consider if drug is wrong?

A

combination or diff drugs

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6
Q

What types of drugs typically need to be monitored?

A
  • narrow therapeutic index
  • variable PK profile (poor correlation between plasma concentration and dose)
  • high risk patients: multimorbidities, polypharmacy/interactions affecting PK
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7
Q

What are examples of drug classes that need monitoring?

A
  • antibiotics
  • cardiovascular
  • immunosuppressants
  • cytotoxic drugs
  • bronchodilators
  • anti-epileptics
  • lithium
  • tricyclic antidepressants
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8
Q

Examples of antibiotics that require therapeutic drug monitoring

A

aminoglycosides (mycins), vancomycin

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9
Q

Examples of anti-epileptics that require therapeutic drug monitoring

A

phenytoin, carbamazepine, valproic acid

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10
Q

Example of cardiovascular drug that requires monitoring

A

digoxin

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11
Q

Examples of cytotoxics that require therapeutic drug monitoring

A

MTX

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12
Q

Examples of bronchodilators that require therapeutic drug monitoring

A

theophylline

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13
Q

What are examples of sampling considerations for monitoring?

A
  • sampling logistics of blood
  • timing
  • free vs total concentration
  • metabolite vs unchanged drug
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14
Q

How is sampling logistics a consideration for therapeutic drug monitoring?

A

sample collection, stability and storage of samples need to be considered

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15
Q

What do you consider with regards to timing and monitoring? What are the exceptions?

A
  • want to ensure steady state reached before measuring (5x half life)
  • exceptions: individualising treatment or aminoglycoside + vancomycin treatment
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16
Q

When considering timing and monitoring for efficacy, what must you do?

A

determine Css right before dosing to ensure drug level are stable

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17
Q

When considering timing and monitoring for toxicity, when do you sample?

A

sample when the highest concentration is expected

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18
Q

When considering timing and you have a drug with a long half-life or multiple compartment PK profile, when do you sample?

A

sample 6-8hrs after dosing

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19
Q

How many approximate half-lives does it take for steady state to be reached?

A

5

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20
Q

Under what circumstances is the free drug concentration measured?
(not routinely)

A

when drug protein and plasma binding is altered due to:

  • medical conditions
  • drug interactions (displacement - acidic drugs for albumin)
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21
Q

What are examples of medical conditions where drug binding is altered?

A
  • renal/hepatic disease
  • malnourishment
  • cystic fibrosis
  • cancer (less albumin present = more drug eliminated as more free drug)
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22
Q

What techniques can be used to separate free and bound drug? 3

A
  • equilibrium dialysis
  • ultrafiltration
  • ultracentrifugation
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23
Q

Under what circumstances would you want to monitor the metabolite concentration?

A
  • if pharmacologically active
  • if it contributes to adverse effects and toxicity
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24
Q

What are examples of analytical techniques used to monitor for metabolites?

A
  • immunoassays
  • liquid chromatography
25
Q

A patient is on the following dosing regimen: losartan, paroxetine and methotrexate for RA. Which drugs are they likely to be monitored for?

A

MTX

26
Q

The same patient begins to experience nausea, vomiting and a low white cell count. What would your course of action be?

A

monitor MTX concentration to see if above maximum effective concentration

27
Q

DDIs….

definition of a DD?

A

a drug affecting efficacy and or toxicity of another drug

28
Q

DDIs categorised based on what 2 things?

A

mechanism
outcome

29
Q

3 sections under mechanism to categorise DDIs?

A

pharmaceutical: int during manufacture, storage, incompatibilities

PK: int changes ADME

PD: activity/tox changed without PK

30
Q

the outcome of a DDI can be
- beneficial
- deleterious

2 examples of DDI that are beneficial?

A

carbidopa + L-dopa

tazobactam + piperacillin

31
Q

DDI may affect absorption rate/ extent.

what 5 things may be affected?

A

gastric emptying
dissolution rate/ pH change
GIT motility
complexation
change in first pass metab

32
Q

drug that may increase gastric emptying?

A

metoclopramide

33
Q

drugs that may change pH?

A

PPI or antacids

34
Q

2 types of drugs that may affect GIT motility (transit time)?

A

opioids
anti-cholinergics

35
Q

2 drugs that may affect complexation therefore absorption?

A

cholestagel
Ca supplements

36
Q

DDIs may affect distribution through change in plasma/ tissue protein binding by doing what?

A

compete for same binding site - drugs w higher affinity/ binding constant displaces the other

often both drugs highly bound to proteins - change to therapeutic response and or tox

37
Q

drug that gets displaced, does fraction existing as free or bound drug increase?

A

free.
this is the form that can distribute, be elim, have pharmacol activity

38
Q

DDI may impact on metabolism and inhibit metabolising enzymes through what….

A

competitive inhibition
non-competitive
onset immediate
reversible
irreversible

39
Q

difference between competitive and non c inhibition?

A

C: both drugs compete for same site
NC: both drugs bind at diff sites

40
Q

onset - inhib of metabolising enzymes - is immediate as soon as what?

A

inhibitor conc high enough to be clinically relevant

41
Q

difference between reversible and non reversible inhibition of metabolising enz?

A

R: immediate return to normal metabolism rates as soon as inhibitor removed

I: return to normal requires synthesis of new enz + px no longer exposed to inhibitor

42
Q

DDI may impact on metabolism and INDUCE metabolising enzymes through what….

A

synthesis of new enz in liver
onset gradual
recovery gradual

43
Q

synthesis of new enz in liver: affect of hepatic Cl, and Css?

A

increase
reduce

44
Q

how long after induer stopped is baseline reached? recovered

A

2-3weeks

45
Q

impact of metabolism effects depend on what?

A

how important metabolism is for drug

drug undergoing extensive FPM… change to BA

46
Q

absorption AND excretion may be impacted through impact on what 2 possible types of transporters?

A

influx/ efflux

47
Q

what specific transporter may be induced/ inhibited?

A

Pgp

dec intestinal abs
dec uptake in bran
inc tubular/bile excretion

(comp, induction, inhibition all possible)

48
Q

if transporters located in kidney/ liver what PK increased?

A

elim

49
Q

if transporters located in SI/ brain what PK increased?

A

absorption

50
Q

2 types of excretion that may be impacted?

A

renal
bile

51
Q

renal excretion may be channged in what 2 methods?

A

changes in urine pH
competition for active tubular secretion sites

52
Q

acidic drugs exreted faster at higher/lower pH

A

higher

53
Q

basic drugs excreted faster at higher/lower pH

A

lower

54
Q

X causes inhibition of renal excretion

A

probenecid

55
Q

aspirin inhibits excretion of what drug?

A

MTX
so adjust MTX dose if both given

56
Q

TF: changing urine pH will change elim rate of ionisable drugs?

A

true

57
Q

bile excretion involes hydrolysis of gut bacteria which ->?

A

enterohepatic recycling -> longer drug effect

58
Q

5 things to consider w DDIs?

A

timeline: onset, duration

predictions

therapeutic index

sequencing: order of drug admin

dose: saturation of processes (high enough conc to become issue)

Lab 3 (21 decks)

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