A hospital's Pharmacy and Therapeutics committee is evaluating a proposal to add a novel anticoagulant, *Thrombostat*, to the formulary for stroke prevention in patients with nonvalvular atrial fibrillation. The committee reviews the primary outcome data from the pivotal, double-blind, randomized controlled trial.
The trial enrolled patients, who were randomized in a ratio to receive either *Thrombostat* or standard-of-care warfarin. Over a 2-year follow-up period, the incidence of the primary endpoint (ischemic stroke) was recorded as follows:
| Treatment Arm | Total Patients () | Number of Ischemic Strokes |
|---|---|---|
| Warfarin | 4000 | 140 |
| *Thrombostat* | 4000 | 60 |
Based on these study results, what is the number needed to treat (NNT) with *Thrombostat* instead of warfarin to prevent one ischemic stroke over 2 years?
Answer: 50 patients
Answer
50
The Number Needed to Treat (NNT) is the number of patients who need to receive a specific treatment (instead of the control) to prevent one additional bad outcome. It is calculated as the inverse of the Absolute Risk Reduction (ARR). First, determine the event rate in the control group (Warfarin): . Next, determine the event rate in the experimental group (*Thrombostat*): . The ARR is the difference between these two rates: . Finally, the NNT is , which equals . This means 50 patients must be treated with *Thrombostat* instead of warfarin over 2 years to prevent one ischemic stroke.
Step-by-Step Solution
Key Concept
Number Needed to Treat (NNT) calculation from clinical trial data