Experts vs Practicing Doctors

In this Study of the Week, we learn about the DCP trial, which compared two ways to treat high blood pressure. Experts preferred one drug; practicing doctors another.

I am in Chicago at the American Heart Association meeting.

On the first day, researchers from Minnesota presented a study that compared two drugs for the treatment of high blood pressure (HBP).

I know, that sounds boring. It’s not though. Hear me out. There are two hooks in this study that make it interesting.

The first of these hooks is that the DCP trial, which stands for Diuretic Comparison Project, studied the experts’ choice for first drug in HBP treatment vs the choice of practicing doctors.

American experts write in their guidelines that practicing doctors should start HBP with a diuretic drug called chlorthalidone. Practicing doctors don’t listen; they use a drug called HCTZ (or hydrochlorothiazide) more than 90% of the time.

The second hook in the DCP trial was how they accomplished the trial. There were no special visits, long consent forms, and super-selective process of finding the perfect patients that are typical of standard trials.

Instead, the researchers embedded the trial into the standard care in the Veteran’s Administration system. Researchers asked VA clinicians if they could consent their patients who were taking HCTZ to be in a trial of HCTZ vs chlorthalidone. We call this a pragmatic trial and it involved more than 12,000 patients.

The findings were clear. After 5 years there were no differences in the primary outcome of stroke, heart attack, non-cancer death, heart failure or need for coronary procedures. However, there were more adverse events in the experts’ choice chlorthalidone, primarily low potassium levels. (Low potassium is bad because it increases the odds for heart rhythm problems).

Comments:

This was an important study because clinicians write millions of prescriptions for HCTZ. If the experts were right, and there was even a tiny benefit from chlorthalidone, it would have been consequential.

But the experts were wrong. They preferred chlorthalidone on the grounds that it was the drug used in the early trials of HBP, and because it had a longer time of action in the body, and because there were some weaker studies suggesting it was the better HBP drug.

In other words, the experts used eminence over evidence to make a recommendation. That is dangerous, and we have too much of it in medicine.

The practicing doctors—with their cumulative wisdom—got this one right. DCP proved that their choice of HCTZ was the correct one.

But I hope you know what my next sentence will be.

We should also not trust the collective wisdom of practicing doctors. I’ve discussed many of the colossal errors we’ve made in accepting therapies that ultimately proved ineffective or harmful.

The way forward, so beautifully shown in the DCP trial, is proper randomized trials.

DCP was special because the investigators showed us a framework for doing a trial pragmatically, without the constraints and expenses of the normal clinical trial. This might be their greatest achievement.

Imagine a future where instead of guessing which drug or procedure is best, doctors have the option to randomize patients into trials that are embedded into the normal practice patterns.

If this were the case medical knowledge will grow by leaps and bounds.