Lecture 2 - Therapeutic Drug Monitoring Flashcards
What does TDM stand for, and how does it aid patient management?
TDM stands for Therapeutic Drug Monitoring. It involves measuring drug concentrations in body fluids to assist in patient management, ensuring that drugs are administered at appropriate levels.
Why is TDM necessary, and what factors can cause variations in drug concentration in a patient’s plasma?
TDM is necessary because there is no standard dose, and drug concentrations can vary due to factors like absorption, metabolism, and elimination. Variations can result from incorrect drug administration, hormonal imbalances, metabolic polymorphisms, diet, and kidney diseases.
Differentiate between pharmacokinetics and pharmacodynamics.
Pharmacokinetics is “what the body does to the drug,” while pharmacodynamics is “what the drug does to the body.”
Explain the concept of the therapeutic range and its components.
The therapeutic range includes therapeutic (desired effects), adverse (undesired effects), therapeutic concentration (minimum effective concentration), adverse concentration (minimum toxic concentration), and the therapeutic range itself (the difference between MTC and MEC). Maintaining a drug in the therapeutic range is essential.
How do therapeutic ranges vary for different drugs, and what factors influence these variations?
Therapeutic ranges vary based on drug toxicity. Non-toxic drugs have a large therapeutic window, medium toxicity drugs have a reasonable window, and highly toxic drugs have a narrow window. The range is influenced by a drug’s bioavailability and other factors.
Define bioavailability (F) in drug administration.
Bioavailability (F) measures how well a drug is absorbed and reaches its site of action. It is calculated as the amount absorbed after oral administration divided by the amount absorbed after IV administration.
What factors affect drug absorption, and how does protein binding impact drug action?
Factors affecting absorption include the stability of the GI tract and hepatic drug metabolism. Extensive protein binding increases the amount of drug that must be absorbed before therapeutic levels of free drug are reached, potentially delaying elimination.
Explain first-order kinetics and its application in drug elimination.
First-order kinetics describe the elimination of most drugs. The rate of elimination is proportional to the plasma concentration, and it is often described as a “one-compartment” model.
Why do some drugs need to be metabolized into more hydrophilic compounds, and what are the criteria for a valid TDM?
Some drugs need metabolism to become more water-soluble for excretion in urine. Valid TDM criteria include drugs with difficult-to-measure pharmacological actions, poor correlation between dose and effect, good correlation between plasma levels and effect, and a narrow therapeutic index.
How can you interpret TDM results when drug levels are lower or higher than expected?
Lower drug levels could be due to non-compliance, poor absorption, fast metabolism, or interactions with other medications. Higher levels could result from excessively high doses, slow metabolism, or drug interactions leading to overdose.
Name and provide the medical uses for three drugs that require TDM.
Three drugs that require TDM include Phenytoin (used for epilepsy), Digoxin (used for atrial fibrillation), and Lithium (used for manic depressive illness).
