Examkin

Question

Difficulty: HardMeasures of Association and Impact

A healthcare committee is evaluating a newly approved oral anticoagulant to replace standard therapy for stroke prevention in patients with nonvalvular atrial fibrillation. The committee reviews data from a randomized, double-blind noninferiority trial involving 5,0005,000 patients. Participants were randomized in a 1:11:1 ratio to receive either the novel anticoagulant or standard therapy and were followed for two years.

The primary efficacy outcome was the incidence of ischemic stroke. The primary safety outcome was the incidence of major bleeding. The trial results are as follows:

OutcomeNovel Anticoagulant (n=2,500n = 2,500)Standard Therapy (n=2,500n = 2,500)
Ischemic stroke7575100100
Major bleeding1001005050

The pharmaceutical representative highlights that the novel anticoagulant reduces the relative risk of stroke by 25%25\% compared to standard therapy. The committee wants to understand the absolute clinical impact of adopting this new medication in their population.

Based on the trial data, which of the following accurately describes the absolute impact of switching patients from standard therapy to the novel anticoagulant?

  1. Treating 100100 patients will prevent 11 stroke, but treating 5050 patients will cause 11 additional major bleeding event.Answer
  2. B
    Treating 44 patients will prevent 11 stroke, but treating 11 patient will cause 11 additional major bleeding event.
  3. C
    Treating 5050 patients will prevent 11 stroke, but treating 100100 patients will cause 11 additional major bleeding event.
  4. D
    Treating 2525 patients will prevent 11 stroke, and treating 5050 patients will cause 11 additional major bleeding event.
  5. E
    The absolute risk reduction for stroke is 25%25\%, and the absolute risk increase for major bleeding is 100%100\%.

Answer

Treating 100100 patients will prevent 11 stroke, but treating 5050 patients will cause 11 additional major bleeding event.
The clinical impact of a new therapy requires assessing both its absolute benefit and absolute harm. The absolute risk reduction (ARR) for stroke is the difference between the standard therapy event rate (4%4\%) and the novel therapy event rate (3%3\%), which equals 1%1\%. The number needed to treat (NNT) is the inverse of the ARR (1/0.01=1001 / 0.01 = 100), meaning 100100 patients must receive the new drug to prevent 11 stroke. Conversely, the absolute risk increase (ARI) for major bleeding is the difference between the novel therapy (4%4\%) and standard therapy (2%2\%), which is 2%2\%. The number needed to harm (NNH) is the inverse of the ARI (1/0.02=501 / 0.02 = 50), meaning treating 5050 patients will cause 11 additional major bleeding event.

Step-by-Step Solution

1
Calculate the event rates for the primary efficacy outcome (stroke) in both groups.
Standard therapy rate = 100/2,500=0.04100 / 2,500 = 0.04 (4%4\%). Novel therapy rate = 75/2,500=0.0375 / 2,500 = 0.03 (3%3\%).
Establishing the absolute event rates is required to find the absolute risk differences between groups.
2
Calculate the Absolute Risk Reduction (ARR) and Number Needed to Treat (NNT) for stroke.
ARR = 4%−3%=1%4\% - 3\% = 1\% (0.010.01). NNT = 1/0.01=1001 / 0.01 = 100.
NNT quantifies the absolute clinical benefit, indicating that 100100 patients must be treated to prevent 11 stroke.
3
Calculate the event rates for the primary safety outcome (major bleeding) in both groups.
Standard therapy rate = 50/2,500=0.0250 / 2,500 = 0.02 (2%2\%). Novel therapy rate = 100/2,500=0.04100 / 2,500 = 0.04 (4%4\%).
Adverse event rates must be calculated to assess the risk of the new intervention.
4
Calculate the Absolute Risk Increase (ARI) and Number Needed to Harm (NNH) for major bleeding.
ARI = 4%−2%=2%4\% - 2\% = 2\% (0.020.02). NNH = 1/0.02=501 / 0.02 = 50.
NNH quantifies the absolute clinical harm, indicating that 5050 patients must be treated to cause 11 additional bleeding event.

Key Concept

Calculation and interpretation of Absolute Risk Reduction (ARR), Absolute Risk Increase (ARI), Number Needed to Treat (NNT), and Number Needed to Harm (NNH).
Rate this question

Topics

Measures of Association and Impact

More questions from this topic