A nurse is reviewing the concept of therapeutic index for medications. Which of the following statements best describes a drug with a narrow therapeutic index?

A. The safe and toxic plasma levels of the drug are very close to each other: A narrow therapeutic index means there is a small margin between the minimum effective concentration and the toxic concentration. Small dosing errors or individual variations in metabolism can lead to toxicity or subtherapeutic effects, requiring close monitoring. B. The drug has a wide range between its effective dose and toxic dose: This describes a drug with a wide therapeutic index, which allows more flexibility in dosing without significant risk of toxicity. Narrow therapeutic index drugs are the opposite and require precise dosing. C. The drug requires infrequent monitoring of serum levels: Medications with a narrow therapeutic index often require frequent serum level monitoring to ensure that the drug stays within the safe and effective range. This helps reduce the risk of adverse effects or treatment failure. D. The drug has a high margin of safety in clinical use: A high margin of safety is characteristic of drugs with a wide therapeutic index. Narrow therapeutic index drugs have a low safety margin and pose higher risks if not carefully dosed and monitored.