Therapeutic Drug Monitoring (TDM) is a clinical practice that involves measuring specific drug concentrations in a patient's bloodstream at designated intervals.
The primary goal is to ensure that drug levels remain within a target therapeutic range, optimizing efficacy while minimizing toxicity.
TDM is particularly crucial for medications with narrow therapeutic indices, significant pharmacokinetic variability, or where therapeutic and toxic concentrations are close.
Need for Therapeutic Drug Monitoring
Narrow Therapeutic Index Drugs
Definition: Small dose variations can lead to serious therapeutic failures or adverse effects.
Examples: Digoxin, lithium, anticonvulsants, aminoglycosides, and vancomycin.
Individual Variability
Pharmacokinetics: Differences in absorption, distribution, metabolism, and excretion affect drug levels.
Genetics: Genetic variations, especially in drug-metabolizing enzymes (e.g., CYP450), impact drug clearance.
Drug Interactions
Polypharmacy: Multiple drugs can interact, affecting drug levels.
Enzyme Modulation: Some drugs induce or inhibit enzymes, altering the pharmacokinetics of others.
Compliance Monitoring
Adherence: Measuring levels helps verify compliance, especially in chronic conditions like epilepsy.
Physiological and Pathological Conditions
Age: Pediatrics and geriatrics may have different pharmacokinetics.
Organ Function: Liver or kidney impairments can significantly alter drug metabolism and excretion.