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Difficulty: MediumMeasures of Disease Frequency and Association

To evaluate the efficacy of a novel sodium-glucose cotransporter-2 (SGLT2) inhibitor in preventing cardiovascular mortality, a multicenter, double-blind trial enrolls patients with chronic heart failure. Participants are randomly assigned to receive either the SGLT2 inhibitor or a placebo. After a median follow-up of three years, the data are analyzed. Among the 2,0002,000 patients in the intervention group, 240240 experienced a cardiovascular mortality event. In the control group, which also consisted of 2,0002,000 patients, 320320 experienced a cardiovascular mortality event. Based on these findings, what is the number needed to treat to prevent one cardiovascular mortality event over the study period?

Answer: 25 patients

Answer

25 patients
The Number Needed to Treat (NNT) represents the number of patients who must receive a particular intervention in order to prevent one additional adverse outcome. It is calculated as 1ARR\frac{1}{ARR} (Absolute Risk Reduction). In this study, the control event rate (CER) is 3202,000=0.16\frac{320}{2,000} = 0.16, and the experimental event rate (EER) is 2402,000=0.12\frac{240}{2,000} = 0.12. The ARR is 0.16−0.12=0.040.16 - 0.12 = 0.04. The inverse of 0.040.04 (10.04\frac{1}{0.04}) yields an NNT of 2525. Therefore, 2525 patients need to be treated with the SGLT2 inhibitor to prevent one cardiovascular mortality event.

Step-by-Step Solution

1
Calculate the Control Event Rate (CER).
CER=3202000=0.16CER = \frac{320}{2000} = 0.16
The baseline risk of the event in the unexposed/placebo population is required to determine how much the treatment reduces that risk.
2
Calculate the Experimental Event Rate (EER).
EER=2402000=0.12EER = \frac{240}{2000} = 0.12
The risk of the event in the treated population is needed to compare against the baseline.
3
Calculate the Absolute Risk Reduction (ARR).
ARR=CER−EER=0.16−0.12=0.04ARR = CER - EER = 0.16 - 0.12 = 0.04
ARR represents the absolute difference in event rates between the two groups.
4
Calculate the Number Needed to Treat (NNT).
NNT=1ARR=10.04=25NNT = \frac{1}{ARR} = \frac{1}{0.04} = 25
NNT is the inverse of ARR, indicating how many patients need to receive the intervention to prevent one additional adverse outcome.

Key Concept

Number Needed to Treat (NNT) is calculated as the inverse of the Absolute Risk Reduction (ARR).
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Topics

Measures of Disease Frequency and Association

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