Examkin

Question

Difficulty: Very hardMeasures of Association and Impact

A 62-year-old man is evaluated in the clinic for optimization of his cardiovascular medications. He has a history of type 2 diabetes mellitus, hypertension, and a myocardial infarction 3 years ago. He currently takes maximal medical therapy, including a high-intensity statin. The physician is considering adding a newly approved oral non-statin lipid-lowering medication.

A recent multinational, randomized controlled trial evaluated this medication in a generalized post-myocardial infarction population. Over a 5-year follow-up period, patients in the placebo arm (who were on standard medical therapy) had a 10%10\% incidence of major adverse cardiovascular events (MACE). The new medication demonstrated a 25%25\% relative risk reduction (RRR) in MACE compared to placebo.

The physician uses a validated clinical risk score incorporating the patient's specific metabolic and cardiovascular parameters and estimates that this particular patient has a 28%28\% baseline probability of experiencing MACE over the next 5 years if he remains on his current regimen.

Assuming the relative risk reduction provided by the new medication is constant across different baseline risk profiles, how many patients with a clinical profile identical to this man's must be treated with the new medication for 5 years to prevent one additional MACE?

  1. A
    4
  2. B
    14
  3. 15Answer
  4. D
    34
  5. E
    40

Answer

15
To determine the true clinical impact of a medication for a specific patient, physicians must calculate an individualized Number Needed to Treat (NNT). While Relative Risk Reduction (RRR) typically remains constant across various patient groups, Absolute Risk Reduction (ARR) and NNT vary inversely with the patient's baseline risk.

First, identify the patient's individualized baseline risk (Control Event Rate, CER), which is given as 28%28\% (0.280.28). Next, apply the trial's RRR (25%25\% or 0.250.25) to calculate the patient-specific ARR using the formula ARR=CER×RRR\text{ARR} = \text{CER} \times \text{RRR}.

ARR=0.28×0.25=0.07\text{ARR} = 0.28 \times 0.25 = 0.07 (or 7%7\%).

Then, calculate the NNT by taking the inverse of the ARR: NNT=1/0.07=14.28\text{NNT} = 1 / 0.07 = 14.28.

Finally, epidemiological convention requires that NNT is always rounded UP to the next whole integer to ensure at least one full event is prevented. Therefore, 14.2814.28 rounds up to 1515.

Step-by-Step Solution

1
Identify the patient's individualized baseline risk of the event.
The patient's Control Event Rate (CER) is 28%28\% or 0.280.28.
Number Needed to Treat (NNT) is a patient-specific absolute metric that heavily depends on the individual's baseline risk, not just the generalized trial population's risk.
2
Identify the expected relative benefit of the intervention.
The Relative Risk Reduction (RRR) from the trial is 25%25\% or 0.250.25.
Relative risk metrics generally remain constant across different risk strata and can be applied to individual patients.
3
Calculate the patient-specific Absolute Risk Reduction (ARR).
ARR = CER \times RRR = 0.28×0.25=0.070.28 \times 0.25 = 0.07 (or 7%7\%).
ARR determines the actual absolute difference in outcomes for this specific patient population.
4
Calculate the Number Needed to Treat (NNT).
NNT = 1/ARR=1/0.07≈14.281 / \text{ARR} = 1 / 0.07 \approx 14.28.
NNT represents the number of patients that must be treated to prevent one adverse event.
5
Apply the rounding convention for NNT.
Round 14.2814.28 up to 1515.
NNT is always rounded up to the next highest whole integer to guarantee the prevention of at least one whole event.

Key Concept

Individualizing Number Needed to Treat (NNT) by applying a trial's Relative Risk Reduction (RRR) to a patient's specific baseline risk (Control Event Rate).
Rate this question

Topics

Measures of Association and Impact

More questions from this topic