A randomized, double-blind, placebo-controlled trial evaluates a new calcitonin gene-relat… — USMLE Step 2 CK

A randomized, double-blind, placebo-controlled trial evaluates a new calcitonin gene-related peptide (CGRP) antagonist for the prevention of chronic migraines. A total of 1,000 adult patients with a history of chronic migraines are enrolled and randomized in a 1:1 ratio to receive either the CGRP antagonist or a matched placebo. The primary study endpoint is the proportion of patients achieving at least a 50% reduction in monthly migraine days over a 12-week period.

At the conclusion of the 12-week study, the following results are reported:
- Placebo group: 150 out of 500 patients met the primary endpoint.
- Treatment group (CGRP antagonist): 275 out of 500 patients met the primary endpoint.

The findings are determined to be statistically significant ( $p < 0.01$ ). Based on these trial results, what is the number needed to treat (NNT) to achieve the primary endpoint in one additional patient? (Provide the exact whole number).

Cevap: 4 patients

Cevap

The Number Needed to Treat (NNT) is the number of patients who must receive a particular treatment to achieve one additional desired outcome (or prevent one adverse outcome) compared to the control group. It is calculated as the inverse of the Absolute Risk Reduction (ARR). In this study, the rate of the desired outcome in the treatment group (EER) is

275 / 500 = 0.55

, and the rate in the placebo group (CER) is

150 / 500 = 0.30

. The ARR is the absolute difference between these rates:

0.55 - 0.30 = 0.25

. Therefore, the NNT is

1 / 0.25 = 4

. This means 4 patients need to be treated with the CGRP antagonist to achieve a 50% reduction in monthly migraine days in one patient who would not have achieved it with the placebo.

Adım Adım Çözüm

Calculate the Control Event Rate (CER).

CER = 150 / 500 = 0.30 (or 30%)

To determine the baseline rate of the outcome in the unexposed/placebo population.

Calculate the Experimental Event Rate (EER).

EER = 275 / 500 = 0.55 (or 55%)

To determine the rate of the outcome in the population exposed to the new intervention.

Calculate the Absolute Risk Reduction (ARR).

ARR = |EER - CER| = |0.55 - 0.30| = 0.25

To quantify the absolute difference in outcome rates between the two groups.

Calculate the Number Needed to Treat (NNT).

NNT = 1 / ARR = 1 / 0.25 = 4

NNT is the inverse of the ARR, representing the number of patients who need to receive the intervention to achieve one additional positive outcome compared to the control.

Anahtar Kavram

The Number Needed to Treat (NNT) is calculated as

1 / ARR

(Absolute Risk Reduction). It represents the number of patients that must be treated with the experimental intervention rather than the control to prevent one additional adverse event or achieve one additional beneficial outcome.

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