Therapeutic Drug Monitoring Flashcards
Drug response variability occurs due to:
1) Pharmacokinetics: Variation in absorption, distribution, metabolism or excretion
2) Pharmacodynamics: Variation at/or beyond tissue receptors or other macromolecular drug targets
What is the continuous variable that must be monitored when dosing?
Biological response;
What is the biological response to a drug closely linked to?
Desired therapeutic outcome of a drug
Drug monitoring is needed to reduce the risk of:
A clinical event (stroke, heart attack, pulmonary
embolism, etc.).
What biological response is monitored when taking antihypertensive drugs?
Blood pressure
What biological response is monitored when taking statins?
Serum cholesterol
What biological response is monitored when taking Warfarin?
International Normalized Ratio (INR)
Is there always a continuous variable to monitor?
No
How can you identify pharmacokinetic variability?
By measuring drug concentrations in plasma or serum
Measuring drug concentrations in plasma or serum may usefully guide:
Dose adjustment
What is therapeutic drug
monitoring?
Measuring drug concentrations in plasma or serum in order to guide dose adjustment.
Measurements of drug concentrations in plasma are most useful when:
1) There is a direct relationship between plasma concentration and pharmacological or toxic effect, and a therapeutic range has been established. (Different dose = bad)
2) Drug effect can NOT readily be assessed quantitatively by clinical observation.
3) Inter-individual variability in plasma drug concentrations from the same dose is large
4) Narrow/low therapeutic index
5) Polypharmacy with anticipation of serious interactions
6) When drug “isn’t working”: “Apparent resistance” to the action of a drug needs an explanation. (when non-compliance is suspected)
Which drugs have an established therapeutic range that shouldn’t be messed around with?
1) Drugs that act via active metabolites
2) Drugs with irreversible actions
What could restrict the usefulness of plasma
concentrations measurement?
Tolerance
Which drug has a very high inter-individual variability?
Phenytoin
Low therapeutic index means:
Ratio of toxic concentration/effective concentration is < 4
What is a non-pharmacological reason for therapeutic
drug monitoring?
Clinical toxicology purposes (Poisoning)
Drug concentration at the site of action is related to:
Drug effect
Drug effect should be proportional to:
Plasma drug concentration
A constant tissue to plasma drug concentration ratio only occurs during:
The terminal β-phase of
elimination
When does the plasma concentration NOT reflect the concentration at the site of action accurately?
Early on in the dosing interval (If you JUST gave the patient his meds, for example)
When should the therapeutic drug monitoring measurements be made?
When distribution of the drug has been completed.
What thing is CRITICAL for the therapeutic drug monitoring measurement to be useful?
Timing of blood sampling
Should you do routine or random blood sampling when therapeutic drug monitoring?
NO
