aTypical Joe: a gay New Yorker living in the rural South

Tuesday, September 26, 2006

Absolute risk

Darshak Sanghavi on the “number needed to treat.” Here he parses the 31% reduction in the risk of heart attacks among men treated with the statin pravastatin:

Suppose that 100 people with high cholesterol levels took statins. Of them, 93 wouldn’t have had heart attacks anyway. Five people have heart attacks despite taking Pravachol. Only the remaining two out of the original 100 avoided a heart attack by taking the daily pills. In the end, 100 people needed to be treated to avoid two heart attacks during the study period-so, the number of people who must get the treatment for a single person to benefit is 50. This is known as the “number needed to treat.”

Developed by epidemiologists in 1988, the NNT was heralded as a new and objective tool to help patients make informed decisions. It avoids the confusing distinction between “relative” and “absolute” reduction of risk. The NNT is intuitive: To a savvy, healthy person with high cholesterol that didn’t decrease with diet and exercise, a doctor could say, “A statin might help you, or it might not. Out of every 50 people who take them, one avoids getting a heart attack. On the other hand, that means 49 out of 50 people don’t get much benefit.” [...]

When a therapy is extremely effective-like surgery for acute appendicitis or insulin for juvenile diabetes-no one worries about NNTs. But most interventions aren’t home runs, and so NNTs are often the only way to tell if they may be worthwhile, medically and economically. Is your shoulder painful and stiff? The NNT for a cortisone shot is three, which is pretty good, but that also means two out of three patients won’t feel any better after the needles. Does your child have an ear infection? Your pediatrician obliges with a bottle of amoxicillin, but the NNT for antibiotics to shorten the duration of fever is more than 20; thus, at least 19 out of 20 parents force the stuff down their toddlers’ throats for no reason. Is your prostate enlarged? The NNT to avoid surgery is 18 if you take Proscar for four years. The drug costs $100 per month per person, so an insurer spends $86,400 to prevent a single surgery for enlarged prostate. Are you thinking of taking aspirin to help avoid a heart attack? The NNT is a lousy 208. Keep in mind that none of these figures include the risks of side effects.

Imagine if this were on every drug container, like the unit price on food. Now that’s a recipe for controlling prescription drug spending!