Benefit–Risk Assessment Using Number Needed to Treat and Number Needed to Harm for Time-to-Event Endpoints

Treatment effect measures under nonproportional hazards

In a clinical trial with a time-to-event endpoint the treatment effect can be measured in various ways. Under proportional hazards all reasonable measures (such as the hazard ratio and the difference in restricted mean survival time) are consistent in the following sense: Take any control group survival distribution such that the hazard rate remains above zero; if there is no benefit by any measure there is no benefit by all measures, and as the magnitude of treatment benefit increases by any measure it increases by all measures. Under nonproportional hazards, however, survival curves can cross, and the direction of the effect for any pair of measures can be inconsistent. In this paper we critically evaluate a variety of treatment effect measures in common use and identify flaws with them. In particular, we demonstrate that a treatment's benefit has two distinct and independent dimensions which can be measured by the difference in the survival rate at the end of follow-up and the difference in restricted mean survival time, and that commonly used measures do not adequately capture both dimensions. We demonstrate that a generalized hazard difference, which can be estimated by the difference in exposure-adjusted subject incidence rates, captures both dimensions, and that its inverse, the number of patient-years of follow-up that results in one fewer event (the NYNT), is an easily interpretable measure of the magnitude of clinical benefit.

Number needed to treat based on real-world evidence for non-vitamin K antagonist oral anticoagulants versus vitamin K antagonist oral anticoagulants in stroke prevention in patients with non-valvular atrial fibrillation

Aims: Non-vitamin K antagonist oral anticoagulants (NOACs) and vitamin K antagonists (VKAs) are used to prevent stroke in patients with atrial fibrillation (AF). This paper aimed to evaluate the clinical efficacy and safety of NOACs when compared to VKAs by calculating the number needed to treat (NNT) at 2 years using incidence rates and hazard ratios (HRs) derived from a meta-analysis of studies conducted in real-world settings. Materials and methods: HRs were sourced from a published systematic literature review and a meta-analysis of real-world evidence on the use of NOACs vs VKAs. Rivaroxaban, dabigatran, and apixaban vs VKAs were investigated. The efficacy outcomes included: a composite of ischaemic stroke and systemic embolism (IS/SE), ischaemic stroke (IS), and all-cause mortality. The safety analysis assessed major bleeding and intracranial haemorrhage (ICH). Results: Superiority of NOACs vs VKAs was observed in 10/15 comparisons. Treating patients with rivaroxaban and dabigatran was associated with a reduced risk of IS and all-cause mortality compared to VKAs, with one death prevented every 22 and 32 patients, respectively, and one IS prevented every 206 and 166 patients, respectively. Rivaroxaban was significantly associated with a reduced risk of IS/SE compared to VKA (NNT: 107). No significant differences were observed between apixaban and VKAs. Dabigatran and apixaban were associated with a reduced risk of major bleeding compared to VKA (NNT: 59 and 38, respectively). No significant difference was observed between rivaroxaban and VKAs regarding major bleeding. Rivaroxaban, dabigatran, and apixaban were significantly associated with a reduced risk of ICH (NNT: 205, 115, and 108, respectively). Limitations: Heterogeneity in definitions of major bleeding across studies. Conclusions: The NNT calculation, when approached and interpreted properly, is a practical measure of the effectiveness of a treatment. The calculation based on HRs showed that NOACs are safe and effective alternatives to VKAs in real life.