Narrow therapeutic drugs need close monitoring because their therapeutic window, effective dose, and safe dose are very close. The small variation in dose leads to greater complications. These drugs can show a response in small doses.
Several factors contribute to therapeutic drug monitoring: specific targets, metabolism variability, drug interaction, tissue sensitivity, individual variability, and dose-response relationship. Due to these factors, drugs with a narrow therapeutic index should be monitored to ensure the safety of the patient and effective drug therapy.
Individual variability, which includes drug effects that vary from person to person, is influenced by various factors such as age, genetics, kidney function, liver function, and other medical conditions. These conditions determine the dose adjustment of a drug.
Variability in drug formulations, including controlled release, sustained release, bioavailability, and pharmacokinetics, can vary.
Some kinds of drugs already have a narrow therapeutic index, such as digitalis, anti-arrhythmics, and immunosuppressants, and require strict monitoring of the dose.
Drug interactions between two drugs occur when one drug increases the dose of the other drug. For example, some drugs increase the activity of warfarin, an anticoagulant. The increased activity can lead to bleeding, so these cases need close monitoring.
Accumulation of a drug occurs when some drugs are not easily eliminated from the body. They accumulate in body organs because they have a long half-life. This accumulation increases the risk of toxicity.
Therapeutic drug monitoring is followed by regular assessments of drug levels in the blood, observation for signs of toxicity or inadequate response, and adjustment of the dose of drugs used in therapy.
