A group of researchers conducted a randomized, double-blind, placebo-controlled trial to study the effectiveness of mercaptopurine and Lactobacillus to prevent recurrence of Crohn disease after surgical resection. Six-hundred patients were randomly assigned to daily mercaptopurine, Lactobacillus, or placebo (ratio: 1:1:1) and followed up for 3 years. Clinical recurrence of Crohn disease was determined based on the Crohn Disease Activity Index (CDAI), with a score 150 indicating recurrence. The primary endpoint was a significant increase in the CDAI (defined as a 100-point increase in score, with CDAI 150) and the need for anti-inflammatory rescue treatment or primary surgical intervention. An excerpt of the study results is shown below. The researchers decide to focus their attention on the effectiveness of mercaptopurine in preventing clinical recurrence events after surgical resection within 3 years compared with placebo. They estimate the number needed to treat to be 10. Which of the following is the correct interpretation of this value?

Question

A group of researchers conducted a randomized, double-blind, placebo-controlled trial to study the effectiveness of mercaptopurine and Lactobacillus to prevent recurrence of Crohn disease after surgical resection.  Six-hundred patients were randomly assigned to daily mercaptopurine, Lactobacillus, or placebo (ratio: 1:1:1) and followed up for 3 years.  Clinical recurrence of Crohn disease was determined based on the Crohn Disease Activity Index (CDAI), with a score >150 indicating recurrence.  The primary endpoint was a significant increase in the CDAI (defined as a 100-point increase in score, with CDAI >150) and the need for anti-inflammatory rescue treatment or primary surgical intervention.  An excerpt of the study results is shown below.  The researchers decide to focus their attention on the effectiveness of mercaptopurine in preventing clinical recurrence events after surgical resection within 3 years compared with placebo.  They estimate the number needed to treat to be 10.  Which of the following is the correct interpretation of this value?

Quizplus · Accepted Answer

Explanation: The number needed to treat (NNT) represents the number of patients who need to be exposed to a treatment (eg, mercaptopurine) to prevent 1 additional adverse outcome (eg, clinical recurrence) in a particular time period (eg, 3 years) compared with a different treatment or control (eg, placebo), assuming the treatment is beneficial. In other words, the NNT compares the effects of 2 interventions in a specific group of people, on a specific outcome, during a predetermined time. Therefore, the NNT will vary depending on the population under consideration, the treatments being compared, the outcomes of interest, and for how long the outcomes were observed. In this case, researchers were interested in the effectiveness of mercaptopurine in preventing clinical recurrence of Crohn disease after surgical resection within 3 years compared with placebo. They estimated the NNT at 10, based on an absolute risk reduction (ARR) between mercaptopurine and placebo as follows: ARR = 23% − 13% = 10% = 0.1NNT = 1 / ARR = 1 / 0.1 = 10 ARR = 23% − 13% = 10% = 0.1 NNT = 1 / ARR = 1 / 0.1 = 10 The correct interpretation for their findings would be that compared with placebo, 10 patients need to be treated with mercaptopurine after surgical resection to prevent 1 additional clinical recurrence within 3 years of treatment. When interpreting the NNT, consider the following questions: What is the baseline risk of patients in the study? What is the comparison group? (Choices B, C, and D) What is the outcome? How long does the study last? (Choice A) Educational objective: The interpretation of the number needed to treat (NNT) should always include information about the comparison group, the specific outcome, and the period of observation for the outcome. NNT values for the same intervention or treatment will vary depending on the outcome, the period of observation, and the comparison group used.

A Group of Researchers Conducted a Randomized, Double-Blind, Placebo-Controlled Trial