What is the therapeutic index and why is it important in nursing practice?

• A. The therapeutic index is the ratio between effective and toxic doses (TI = ED50/TD50); a narrow TI requires careful monitoring and dosing.
• B. The therapeutic index is the ratio between toxic and effective doses (TI = TD50/ED50); a narrow TI requires careful monitoring and dosing.
• C. The TI is the difference between peak and trough levels.
• D. TI indicates dosage frequency only.

Answer: (B)