A 42-year-old woman comes to the office for a routine follow-up. She was diagnosed with multiple sclerosis 3 months ago and has had no relapses since. She had previously preferred not to take any medications for multiple sclerosis, but she is now interested in finding out about different treatments. The patient has no other medical problems. She does not use tobacco, alcohol, or illicit drugs. Examination shows no abnormalities. A new treatment A is available that is apparently highly effective in preventing multiple sclerosis relapses. A randomized trial shows that the incidence of relapses was 20% after 6 months of treatment A. Patients managed with placebo had an incidence of 25% during the same time period. Considering this information, how many patients will need to be treated with treatment A in order to prevent 1 episode of relapse of multiple sclerosis during the first 6 months of therapy?
A)Four patients
B)Eight patients
C)Twenty patients
D)Ten patients
E)Five patients

Question

A 42-year-old woman comes to the office for a routine follow-up.  She was diagnosed with multiple sclerosis 3 months ago and has had no relapses since.  She had previously preferred not to take any medications for multiple sclerosis, but she is now interested in finding out about different treatments.  The patient has no other medical problems.  She does not use tobacco, alcohol, or illicit drugs.  Examination shows no abnormalities.  A new treatment A is available that is apparently highly effective in preventing multiple sclerosis relapses.  A randomized trial shows that the incidence of relapses was 20% after 6 months of treatment A.  Patients managed with placebo had an incidence of 25% during the same time period.  Considering this information, how many patients will need to be treated with treatment A in order to prevent 1 episode of relapse of multiple sclerosis during the first 6 months of therapy?
A)Four patients
B)Eight patients
C)Twenty patients
D)Ten patients
E)Five patients

Quizplus · Accepted Answer

Explanation: The number needed to treat (NNT) is a useful measure to evaluate the efficacy of a therapy and the risk of adverse events, which can sometimes outweigh the benefits. In order to calculate the NNT, the absolute risk reduction (ARR) must first be determined. The ARR can be obtained by subtracting the risk of relapses in the treatment group from that of the placebo group: ARR = 0.25 - 0.20 = 0.05 (ie, 5%). This means that for every 100 patients who used treatment A, 5 patients showed improvement. The NNT is equal to 1/ARR. Therefore, NNT = 1/ARR = 1/0.05 = 20. This means that 20 patients need to be treated in order to prevent one multiple sclerosis relapse during the first 6 months of therapy. Educational objective: The number needed to treat (NNT) is the number of patients that need to be treated in order to prevent or cure one disease or medical condition. NNT is a useful measure to evaluate the efficacy of a given therapy. It is calculated by getting the inverse of the absolute risk reduction (ARR); in other words, NNT = 1/ARR.

A 42-Year-Old Woman Comes to the Office for a Routine