RN Exam Practice
Pharmacological and Parenteral TherapiesQuestion 1732 of 2368

A client is starting phenytoin for seizures and will have frequent peak and trough levels drawn. What is the reason for this monitoring?

  1. The drug has a narrow range between effective and toxic concentrations
  2. The drug has a very wide margin between effective and toxic concentrations
  3. The drug is always eliminated from the body at a constant rate each day
  4. The drug is not protein-bound, so levels cannot be predicted from the dose
Show answer

Correct answer: The drug has a narrow range between effective and toxic concentrations

A narrow therapeutic index means little difference between effective and toxic doses. Levels confirm a therapeutic dose without toxicity.

Source: Nursing Pharmacology, 2nd edition (Open RN, Chippewa Valley Technical College, 2023), Pharmacokinetics & Pharmacodynamics: Therapeutic Index. Licensed under CC BY 4.0.

Practice the topic "Pharmacological and Parenteral Therapies"

Questions last reviewed: 18 October 2026