July 20, 2010

Number Needed to Treat

The Number Needed to Treat (NNT) is a hot concept in Evidence-Based Medicine since it provides a simple statistic that is a simple way for clinicians to objectively determine the effectiveness of a treatment. It is defined by wikipedia as:
... an epidemiological measure used in assessing the effectiveness of a health-care intervention, typically a treatment with medication. The NNT is the number of patients who need to be treated in order to prevent one additional bad outcome (i.e. the number of patients that need to be treated for one to benefit compared with a control in a clinical trial). It is defined as the inverse of the absolute risk reduction. It was described in 1988. The ideal NNT is 1, where everyone improves with treatment and no-one improves with control. The higher the NNT, the less effective is the treatment
That being said, EVERY medication has a number needed to treat that is greater than one. So what are some common NNTs in medicine? The answer may surprise you.

Dr. Shaughnessy from Tufts Family Medicine pulled out a select few that I thought were notable.

Condition Treatment Outcome* NNT
Hypertension in patients with type 2 diabetes Hypertension treatment Diabetes-related death over 10 years 15
Hyperlipidemia (secondary prevention) Various versus placebo Heart attack or stroke over five years 16
Hyperlipidemia (primary prevention) Simvastatin versus no treatment Death over one year 163
Peptic ulcer Helicobacter pylori eradication therapy versus acid suppression treatment for six to eight weeks Cure at one year 1.8
Migraine Sumatriptan versus placebo Headache relief at two hours 2.6

A more extensive list can be found at Table of NNTs on Bandolier