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Difficulty: Very hardMedical Literature and Drug Advertisement Interpretation

A physician is evaluating a promotional brochure for a newly approved biologic agent for the prevention of cardiovascular events in high-risk patients. The brochure prominently features a bar graph illustrating a 40%40\% relative risk reduction (RRR) in the primary composite endpoint (nonfatal myocardial infarction, nonfatal stroke, and cardiovascular death) over a 4-year period compared to placebo.

To better understand the data, the physician reviews the trial methodology in the accompanying package insert. In the clinical trial, the absolute risk of the primary composite endpoint in the placebo group was 20%20\% over 4 years. The medication was also associated with an increased incidence of injection-site reactions, with a calculated number needed to harm (NNH) of 25 over 4 years.

The physician is considering prescribing this biologic agent to a 55-year-old man with hyperlipidemia. Using a validated cardiovascular risk calculator, the physician estimates that this specific patient's absolute risk for experiencing the primary composite endpoint without the biologic treatment is 5%5\% over the next 4 years.

Assuming the relative risk reduction of the medication remains constant across different baseline risk levels, what is the calculated number needed to treat (NNT) to prevent one primary composite endpoint event over 4 years for a population with this patient's specific baseline risk profile?

Answer: 50 patients

Answer

50
The correct calculated Number Needed to Treat (NNT) for this specific patient is 50. In evidence-based medicine, relative risk reduction (RRR) is typically assumed to be constant across varying levels of baseline risk, whereas absolute risk reduction (ARR) and NNT vary significantly depending on the patient's initial risk. To find the patient-specific NNT, first determine the patient's expected baseline risk (Control Event Rate, CER), which is 5%5\% (0.050.05). Multiply the CER by the trial's RRR (40%40\% or 0.400.40) to find the patient-specific ARR: 0.05×0.40=0.020.05 \times 0.40 = 0.02. The NNT is the inverse of the ARR: 10.02=50\frac{1}{0.02} = 50. This means 50 patients with a risk profile similar to this 55-year-old man must be treated for 4 years to prevent one composite cardiovascular event.

Step-by-Step Solution

1
Identify the patient's specific baseline risk (Control Event Rate, CER).
Patient CER = 5%5\% or 0.050.05 over 4 years.
NNT for an individual patient must be calculated using their own baseline risk, not the trial's average risk.
2
Identify the relative risk reduction (RRR) of the intervention.
RRR = 40%40\% or 0.400.40.
RRR is provided in the drug advertisement and is generally assumed to be constant across different baseline risk groups.
3
Calculate the patient-specific absolute risk reduction (ARR).
ARR=CER×RRR=0.05×0.40=0.02\text{ARR} = \text{CER} \times \text{RRR} = 0.05 \times 0.40 = 0.02 (or 2%2\%).
ARR depends on the baseline risk and determines the actual absolute benefit the patient will receive.
4
Calculate the number needed to treat (NNT).
NNT=1ARR=10.02=50\text{NNT} = \frac{1}{\text{ARR}} = \frac{1}{0.02} = 50.
NNT is the inverse of the ARR.

Key Concept

Applying trial-derived relative risk reduction (RRR) to a patient's individualized baseline risk to calculate a patient-specific number needed to treat (NNT).
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Medical Literature and Drug Advertisement Interpretation

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