Number needed to harm

There may be some situations where the test treatment is, in fact, harmful relative to the control treatment in terms of a particular endpoint. In these circumstances it does not make sense to take talk about number needed to treat and we refer instead to number needed to harm (NNH). So, for example, if the survival rate on the test treatment were 72 per cent compared to 84 per cent in the control group then the number needed to harm would be equal to 1 /(0.84 — 0.72) which rounds to eight. 

EBM, evidence-based medicine NNH, number needed to harm NNT, number needed to treat. 

Abbreviations D, death MI, myocardial infarction NNH, numbers needed to harm NNT, numbers needed to treat PCI, percutaneous coronary inteivention STEMI, ST-elevation myocardial infraction UR, urgent reintervention. 

The adverse effects of thiazide and thiazide-like diuretics on male sexual function include reduced libido, erectile dysfunction, and difficulty in ejaculating. The exact incidence of sexual dysfunction in patients taking diuretics is poorly documented, perhaps because of the personal nature of the problem and the reluctance of patients and/or physicians to discuss it. However, these abnormalities have been reported with incidence rates of 3-32%. The true incidence of sexual dysfunction probably lies closer to the lower end of this range (119). In a meta-analysis of 13 randomized, placebo-controlled trials conducted over a mean of 4 years the NNH (number needed to harm) for erectile impotence with thiazide diuretics in hypertension was 20 and the relative risk was 5.0 (120). 

TABLE 3—5. Number Needed to Treat and Number Needed to Harm... 

Thus the NNT is 46. That is, treating 46 patients with unstable angina for 9 months with aspirin with clopidogrel should prevent Ml, stroke, or CV death in 1 patient. To balance risks versus benefits of an intervention, we can generate a similar number needed to harm to express the risks associated to the intervention. 

To calculate the number needed to harm (NNH), first calculate the absolute risk increase (ARI). This is the absolute difference between the event rate in the experimental group (EER) minus the event rate in the control group (CER). The NNH is the inverse of the ARI. 

Number needed to harm since CEE -I- MPA was worse than placebo. 

Furthermore, using the risk ratio to ensure safety ignores the clinical relevance of the baseline risk and can lead to very different numbers needed to harm (NNH) to satisfy the definition of "safe." For instance, if the hazard ratio must be < 1.3 and the control rate is 0.5 events per 100 patient-years, then the NNH is 1/(1.3 x 0.005 - 0.005) = 667 patients. Whereas if the control rate is 3 events per 100 patient-years, then the NNH is 1/(0.039 - 0.030) = 111. In one case, "safe" must have an NNH better than 667, and in the other, an additional CV event for every 111 treated patients might be deemed "safe." Clinically one could argue if the baseline CV event rate is very low, the allowed maximum hazard ratio should be a bit larger— a greater hazard ratio will still produce fewer additional events when the baseline risk is low. This can be done without increasing the NNH. 

Alternatively, for an AE of interest, number needed to harm (NNH) can be calculated similarly as... 

Citrome L. Miracle pills for weight loss what is the number needed to treat, number needed to harm and likelihood to be helped or harmed for naltrexone-bupropion combination Int J Clin Pract 2010 64(11) 1462-5. 

Kowalska JD, Kirk O, Mocroft A, Hoj L, Friis-M0ller N, Reiss P, Weller I, Lundgren JD. Implementing the number needed to harm in clinical practice risk of myocardial infarction in HIV-l-infected patients treated with abacavir. HIV Med 2010 11(3) 200-8. 

Gastrointestinal In a systematic review the efficacy and safety of neuromodulators for pain management in patients with inflammatory arthritis was evaluated. Three trials (on Rheumatoid arthritis patients) were included. Nefopam was associated with significantly more adverse events (RR 4.1 95%CI 1.6-10.7) with a number needed to harm of 9 (95%CI 2-367), and consisted predominantly of nausea (56%) and sweating (44%) [51 ]. 

Recent publications on major clinical trials whose implications will involve a recommendation to change clinical practice have included summary statistics that quantify the risk of benefit or harm that may occur if the results of a given trial are strictly applied to an individual patient or to a representative cohort. Four simple calculations will enable the non-statistician to answer the simple question How much better would my chances be (in terms of a particular outcome) if I took this new medicine, than if I did not take it . These calculations are the relative risk reduction, the absolute risk reduction, the number needed to treat, and the odds ratio (see Box 6.3). 

I. 18-1.62), number-needed-to-treat (NNT) was 6 for complete control of nausea relative risk was 1.28 (Cl 1.08-1.51), NNT 8 for complete control of vomiting. Cannabinoids were not more effective in patients receiving very low or very high emetogenic chemotherapy. In crossover trials, patients preferred cannabinoids for future chemotherapy cycles relative risk 2.39 (2.05-2.78), NNT 3. Some potentially beneficial side effects occurred more often with cannabinoids high 10.6 (6.86-16.5), NNT 3 sedation or drowsiness 1.66 (1.46-1.89), NNT 5 euphoria 12.5 (3-52.1), NNT 7. Harmful side effects also occurred more often with cannabinoids dizziness 2.97 (2.31-3.83), NNT 3 dysphoria or depression 8.06 (3.38-19.2), NNT 8 hallucinations 6.10 (2.41-15.4), NNT 17 paranoia 8.58 (6.38-... 

Saver, J.L., et al.. Number needed to treat to benefit and to harm for intravenous tissue plasminogen activator therapy in the 3- to 4.5-hour window joint outcome table analysis oftheECASS3trial. Stroke, 2009. 40(7) p. 2433-7. 

NNT, NNTb, NNTh number needed to treat [for benefit, for harm]... 

Moreover, the strength of current signal detection systems is in detecting new or unexpected findings, often relating to more extreme phenotypes of adverse reactions that have low background incidences. This gives us only a small snapshot of the beast, and we are seldom able to derive clinically important measures, such as the relative risk and its confidence intervals, or absolute estimates of risk, such as the likely number of patients affected or the number needed to treat for harm (NNTh). 

The link between exposure to air pollutants and adverse health effects is well established, but the causal biological mechanisms are not clear and this is especially the case for particulate matter health effects. Airborne particulate matter is extremely variable in chemical composition, size and morphology all parameters of possible health relevance. This and the different health endpoints affected by exposure to ambient PM make the situation very complex. It may well be that more than one particle characteristic is needed to effectively describe the harmful outcomes of exposure. Possible parameters under discussion are particle number concentration, which is dominated by particles below 100 nm in size the so-called ultrafines [33], particle surface area concentration, which is dominated by particles around 200-800 nm in diameter [34, 35], black carbon or black smoke [36], or the reactivity of particles with respect to redox reactions, or their potential to form radical oxidative species (ROS) [37]. These and some other alternative particulate indicators are currently discussed [38] and investigated in several large European and US studies such as ESCAPE and Transphorm2. 

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