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

PK: therapeutic drug monitoring + DDIs Flashcards

(58 cards)

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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?

Study These Flashcards
A
  • immunoassays
  • liquid chromatography
25
A patient is on the following dosing regimen: losartan, paroxetine and methotrexate for RA. Which drugs are they likely to be monitored for?
MTX
26
The same patient begins to experience nausea, vomiting and a low white cell count. What would your course of action be?
monitor MTX concentration to see if above maximum effective concentration
27
DDIs.... definition of a DD?
a drug affecting efficacy and or toxicity of another drug
28
DDIs categorised based on what 2 things?
mechanism outcome
29
3 sections under mechanism to categorise DDIs?
pharmaceutical: int during manufacture, storage, incompatibilities PK: int changes ADME PD: activity/tox changed without PK
30
the outcome of a DDI can be - beneficial - deleterious 2 examples of DDI that are beneficial?
carbidopa + L-dopa tazobactam + piperacillin
31
DDI may affect absorption rate/ extent. what 5 things may be affected?
gastric emptying dissolution rate/ pH change GIT motility complexation change in first pass metab
32
drug that may increase gastric emptying?
metoclopramide
33
drugs that may change pH?
PPI or antacids
34
2 types of drugs that may affect GIT motility (transit time)?
opioids anti-cholinergics
35
2 drugs that may affect complexation therefore absorption?
cholestagel Ca supplements
36
DDIs may affect distribution through change in plasma/ tissue protein binding by doing what?
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
drug that gets displaced, does fraction existing as free or bound drug increase?
free. this is the form that can distribute, be elim, have pharmacol activity
38
DDI may impact on metabolism and inhibit metabolising enzymes through what....
competitive inhibition non-competitive onset immediate reversible irreversible
39
difference between competitive and non c inhibition?
C: both drugs compete for same site NC: both drugs bind at diff sites
40
onset - inhib of metabolising enzymes - is immediate as soon as what?
inhibitor conc high enough to be clinically relevant
41
difference between reversible and non reversible inhibition of metabolising enz?
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
DDI may impact on metabolism and INDUCE metabolising enzymes through what....
synthesis of new enz in liver onset gradual recovery gradual
43
synthesis of new enz in liver: affect of hepatic Cl, and Css?
increase reduce
44
how long after induer stopped is baseline reached? recovered
2-3weeks
45
impact of metabolism effects depend on what?
how important metabolism is for drug drug undergoing extensive FPM... change to BA
46
absorption AND excretion may be impacted through impact on what 2 possible types of transporters?
influx/ efflux
47
what specific transporter may be induced/ inhibited?
Pgp dec intestinal abs dec uptake in bran inc tubular/bile excretion (comp, induction, inhibition all possible)
48
if transporters located in kidney/ liver what PK increased?
elim
49
if transporters located in SI/ brain what PK increased?
absorption
50
2 types of excretion that may be impacted?
renal bile
51
renal excretion may be channged in what 2 methods?
changes in urine pH competition for active tubular secretion sites
52
acidic drugs exreted faster at higher/lower pH
higher
53
basic drugs excreted faster at higher/lower pH
lower
54
X causes inhibition of renal excretion
probenecid
55
aspirin inhibits excretion of what drug?
MTX so adjust MTX dose if both given
56
TF: changing urine pH will change elim rate of ionisable drugs?
true
57
bile excretion involes hydrolysis of gut bacteria which ->?
enterohepatic recycling -> longer drug effect
58
5 things to consider w DDIs?
timeline: onset, duration predictions therapeutic index sequencing: order of drug admin dose: saturation of processes (high enough conc to become issue)

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