Examkin

Question

Difficulty: MediumMeasures of Disease Frequency and Association

A clinical investigator is conducting a randomized, double-blind, placebo-controlled trial to evaluate the efficacy of a new monoclonal antibody targeting interleukin-5 (IL-5) for the prevention of severe exacerbations in patients with uncontrolled eosinophilic asthma. A total of 2,000 patients are enrolled and equally divided into two groups: one receiving the monoclonal antibody and the other receiving a placebo. All patients are followed for 1 year. During the follow-up period, 150 patients in the placebo group and 100 patients in the treatment group experience at least one severe asthma exacerbation. Which of the following is the number needed to treat to prevent one additional severe asthma exacerbation in this patient population over 1 year?

  1. A
    3
  2. B
    10
  3. 20Answer
  4. D
    50
  5. E
    67

Answer

20
The Number Needed to Treat (NNT) is the number of patients who need to receive a specific intervention instead of the control to prevent one additional adverse outcome. It is calculated by taking the reciprocal of the Absolute Risk Reduction (ARR). First, calculate the event rates for each group. The total population is 2,000, equally divided into 1,000 per group. The Control Event Rate (CER) is 150/1000=0.15150 / 1000 = 0.15 (15%15\%). The Experimental Event Rate (EER) is 100/1000=0.10100 / 1000 = 0.10 (10%10\%). The ARR is the difference between these rates: 0.15−0.10=0.050.15 - 0.10 = 0.05 (5%5\%). The NNT is 1/0.051 / 0.05, which equals 2020. Therefore, 20 patients need to be treated with the monoclonal antibody for 1 year to prevent one severe asthma exacerbation.

Step-by-Step Solution

1
Calculate the Control Event Rate (CER).
CER = 150/1000=0.15150 / 1000 = 0.15 or 15%15\%.
Determines the baseline risk of severe exacerbations in the placebo group.
2
Calculate the Experimental Event Rate (EER).
EER = 100/1000=0.10100 / 1000 = 0.10 or 10%10\%.
Determines the risk of severe exacerbations in the monoclonal antibody group.
3
Calculate the Absolute Risk Reduction (ARR).
ARR = CER - EER = 0.15−0.10=0.050.15 - 0.10 = 0.05 or 5%5\%.
ARR represents the absolute difference in risk between the control and experimental groups.
4
Calculate the Number Needed to Treat (NNT).
NNT = 1/ARR=1/0.05=201 / \text{ARR} = 1 / 0.05 = 20.
NNT is the reciprocal of the ARR and indicates how many patients must be treated to prevent one adverse event.

Key Concept

The Number Needed to Treat (NNT) is calculated as the inverse of the Absolute Risk Reduction (ARR), which is the absolute difference in event rates between the control and experimental groups.
Estimated Time:1m 15s
Rate this question

Topics

Measures of Disease Frequency and Association

More questions from this topic