Question

a client asks the nurse to explain the meaning of a narrow therapeutic index of a medication. which information should the nurse use to answer the question?
the onset of action for the medication occurs very quickly.
a small margin exists between safe and toxic plasma levels.
bioavailability is significantly reduced by the first - pass effect.
minimum dosage is needed for the medication to be effective.

Explanation:

To answer the question about the narrow therapeutic index of a medication, we analyze each option:

• The first option (onset of action quickly) is about how fast the drug works, not related to therapeutic index.
• The second option: A narrow therapeutic index means the difference between the dose that produces a therapeutic effect and the dose that produces toxicity (toxic plasma levels) is small. So this option correctly describes it.
• The third option (bioavailability and first - pass effect) is about how much of the drug is available in the body after administration, not about therapeutic index.
• The fourth option (minimum dosage for effectiveness) is about the effective dose, not the relationship between safe and toxic levels which is what therapeutic index is about.

Answer:

B. A small margin exists between safe and toxic plasma levels.