Lesson 13: The Number-Needed-to Treat (NNT)
Healthcare for Policymakers
In the last lesson we discussed the risk-benefit-cost ratio which should be the underpinning of all medical decision making. The NNT is an easy way to compare the efficacy of a medical intervention. It tells us how many patients need to be treated with a particular therapy to prevent one event. The NNT is the best measure of efficacy of a medical treatment.
Think of it like this: Let's say you have 100 patients with a condition. You're trying to decide if a new drug is worth using. You know that the standard treatment has a certain risk of a bad outcome, like a heart attack. The NNT for the new drug tells you how many of those 100 patients need to be treated with the drug to prevent ONE heart attack compared to the standard treatment.A lower NNT means the treatment is more effective, since fewer people need to be treated to see a benefit. For example, an NNT of 3 means that you need to treat three people to prevent one heart attack, while an NNT of 10 means you need to treat 10 people to prevent one heart attack.
The NNT can help you and your doctor make informed decisions about treatment options. It's a valuable tool that can help us to understand the potential benefits of different treatments, and to weigh those benefits. This calculation is especially useful if you are trying to understand they efficacy of treatments for diabetes and heart disease. For example, you can’t watch television for an hour without seeing a commercial for Wegovy or Ozempic. Ozempic is a drug approved to lower the blood sugar in patients who have type 2 diabetes. The adds also say that Ozempic lowers the cardiovascular risk in patients with diabetes and that is very important because high sugar does not kill people with diabetes. They die of vascular disease. The obvious next question is this. How effective is Ozempic in preventing cardiovascular events?
The higher the cardiovascular risk of a population, the more effective a treatment like Ozempic is in lowering the risk of a major cardiovascular event (cardiovascular death, non-fatal stroke, non-fatal myocardial infarction). In patients with type 2 diabetes and a moderate to high cardiovascular risk, the NNT to prevent a major cardiovascular event is 111 with Ozempic. With Jardiance, you must treat 43 patients to prevent a cardiovascular death. The NNT for aspirin in type diabetes to prevent a major cardiovascular event is 91. For statins, the NNT is 35.
But that is not the end of the story. Treating type 2 diabetes is not just about lowering the blood sugar. It is also about lowering the blood pressure, the cholesterol, stopping smoking, and taking an aspirin if you have a high risk. It is critically important how you lower the blood pressure and the blood sugar. There is no NNT value to cite for intensive blood sugar and blood pressure lowering. In the landmark ACCORD trial, intensive glucose lowering to near normal using any drug approved for the purpose resulted in increased mortality and no reduction in major cardiovascular events. Two other studies (ADVANCE and VADT) of intensive glucose lowering using any approved drug also failed to reduce major cardiovascular events. Using any approved drug to lower the glucose is our current model— usual care— the care that most Americans receive.
There is a much more powerful approach to type 2 diabetes and the NNT proves its superiority. In high-risk patients with diabetes and chronic kidney disease treated with optimal medical therapy in the Steno 2 trial, after 8 years the NNT to prevent a major cardiovascular event was 5 compared with usual care. That proves a huge advantage of optimal medical therapy over other types of care. The Steno 2 trial had equally aggressive targets for blood sugar, blood pressure, and cholesterol (OMT) for type 2 diabetes has an NNT of 5. The NNT for Ozempic is over one hundred. Ozempic costs someone about $1000 a month. OMT is 20 times as effective as Ozempic at one twentieth the cost. The authors of the Steno 2 trial made this critical statement 20 years ago. “The challenge for now is to ensure that the trial experiences are widely adopted in daily clinical practice.” I agree entirely. That is what we must do. The number needed to treat data gives us clear direction on what works and what should happen next. We all have a stake in this. The best care is the least expensive care and the most effective care. Every single person who understands can tell their friends and family and make a difference.