There was no difference in major cardiovascular outcomes with the use of two different diuretics — chlorthalidone or hydrochlorothiazide — in the treatment of hypertension in a new large randomized real-world study.

The Diuretic Comparison Project (DCP), which was conducted in more than 13,500 U.S. veterans age 65 years or over, showed almost identical rates of the primary composite endpoint, including myocardial infarction (MI), stroke, noncancer death, hospitalization for acute heart failure, or urgent revascularization, after a median of 2.4 years of follow-up.

There was also no difference in any of the individual endpoints or other secondary cardiovascular outcomes.

However, in the subgroup of patients who had a history of MI or stroke (who made up about 10% of the study population), there was a significant reduction in the primary endpoint with chlorthalidone, whereas those without a history of MI or stroke appeared to have an increased risk for primary outcome events while receiving chlorthalidone compared with those receiving hydrochlorothiazide.

The DCP trial was presented today at the American Heart Association (AHA) Scientific Sessions 2022, by Areef Ishani, MD, director of the Minneapolis Primary Care and Specialty Care Integrated Care Community and director of the Veterans Administration (VA) Midwest Health Care Network.

Asked how to interpret the result for clinical practice, Ishani said, “I think we can now say that either of these two drugs is appropriate to use for the treatment of hypertension.”

But he added that the decision on what to do with the subgroup of patients with previous MI or stroke was more “challenging.”

“We saw a highly significant benefit in this subgroup, but this was in the context of an overall negative trial,” he noted. “I think this is a discussion with the patients on how they want to hedge their bets. Because these two drugs are so similar, if they wanted to take one or the other because of this subgroup result I think that is a conversation to have, but I think we now need to conduct another trial specifically in this subgroup of patients to see if chlorthalidone really is of benefit in that group.”

Ishani explained that both chlorthalidone and hydrochlorothiazide have been around for more than 50 years and are considered first-line treatments for hypertension. Early studies suggested better cardiovascular outcomes and 24-hour blood pressure control with chlorthalidone, but recent observational studies have not shown more benefit with chlorthalidone. These studies have suggested that chlorthalidone may be associated with an increase in adverse events, such as hypokalemia, acute kidney injury, and chronic kidney disease.

Pragmatic Study

The DCP trial was conducted to try to definitively answer this question of whether chlorthalidone is superior to hydrochlorothiazide. The pragmatic study had a “point-of-care” design that allowed participants and healthcare professionals to know which medication was being prescribed and to administer the medication in a real-world setting.

“Patients can continue with their normal care with their usual care team because we integrated this trial into primary care clinics,” Ishani said. “We followed participant results using their electronic health record. This study was nonintrusive, cost-effective, and inexpensive. Plus, we were able to recruit a large rural population, which is unusual for large, randomized trials, where we usually rely on big academic medical centers.”

Using VA electronic medical records, the investigators recruited primary care physicians, who identified patients older than age 65 years who were receiving hydrochlorothiazide (25 mg or 50 mg) for hypertension. These patients (97% of whom were male) were then randomly assigned to continue receiving hydrochlorothiazide or to switch to an equivalent dose of chlorthalidone. Patients were followed through the electronic medical record as well as Medicare claims and the National Death Index.

Results after a median follow-up of 2.4 years showed no difference in blood pressure control between the two groups.

In terms of clinical events, the primary composite outcome of MI, stroke, noncancer death, hospitalization for acute heart failure, or urgent revascularization occurred in 10.4% of the chlorthalidone group and in 10.0% of the hydrochlorothiazide group (hazard ratio [HR], 1.04; 95% CI, 0.94 – 1.16; P = .4).

There was also no difference in any individual components of the primary endpoint or the secondary outcomes of all-cause mortality, any revascularization, or erectile dysfunction.

In terms of adverse events, chlorthalidone was associated with an increase in hypokalemia (6% vs 4.4%; HR, 1.38), but there was no difference in hospitalization for acute kidney injury.

Benefit in MI, Stroke Subgroup?

In the subgroup analysis, patients with a history of MI or stroke who were receiving chlorthalidone had a significant 27% reduction in the primary endpoint (HR, 0.73; 95% CI, 0.57 – 0.94). Conversely, patients without a history of MI or stroke appeared to do worse while taking chlorthalidone (HR, 1.12; 95% CI, 1.00 – 1.26).

“We were surprised by these results,” Ishani said. “We expected chlorthalidone to be more effective overall. However, learning about these differences in patients who have a history of cardiovascular disease may affect patient care. It’s best for people to talk with their healthcare clinicians about which of these medications is better for their individual needs.”

He added: “More research is needed to explore these results further because we don’t know how they may fit into treating the general population.”

Ishani noted that a limitations of this study was that most patients were receiving the low dose of chlorthalidone, and previous studies that suggested benefits with chlorthalidone used the higher dose.

“But the world has voted — we had 4000 clinicians involved in this study, and the vast majority are using the low dose of hydrochlorothiazide. And this is a definitively negative study,” he said. “The world has also voted in that 10 times more patients were on hydrochlorothiazide than on chlorthalidone.”

Commenting on the study at an AHA press conference, Biykem Bozkurt, Baylor College of Medicine, Houston, Texas, pointed out that in all of the landmark National Institutes of Health hypertension trials, there was a signal for benefit with chlorthalidone compared with other antihypertensives.

“We’ve always had this concept that chlorthalidone is better,” she said. “But this study shows no difference in major cardiovascular endpoints. There was more hypokalemia with chlorthalidone, but that’s recognizable as chlorthalidone is a more potent diuretic.”

Other limitations of the DCP trial are its open-label design, which could interject some bias; the enduring effects of hydrochlorothiazide — most of these patients were receiving this agent as background therapy; and inability to look at the effectiveness of decongestion of the agents in such a pragmatic study, Bozkurt noted.

She said she would like to see more analysis in the subgroup of patients with previous MI or stroke. “Does this result mean that chlorthalidone is better for sicker patients or is this result just due to chance?” she asked.

“While this study demonstrates equal effectiveness of these two diuretics in the targeted population, the question of subgroups of patients for which we use a more potent diuretic I think remains unanswered,” she concluded.

Designated discussant of the DCP trial at the late-breaking trial session, Daniel Levy, MD, director of the Framingham Heart Study at the National Heart, Lung, and Blood Institute, reminded attendees that chlorthalidone had shown impressive results in previous important hypertension studies including SHEP and ALLHAT.

He said the current DCP was a pragmatic study addressing a knowledge gap that “would never have been performed by industry.”

Levy concluded that the results showing no difference in outcomes between the two diuretics were “compelling,” although a few questions remain.

These include a possible bias toward hydrochlorothiazide — patients were selected who were already taking that drug and so would have already had a favorable response to it. In addition, because the trial was conducted in an older male population, he questioned whether the results could be generalized to women and younger patients.

The DCP study was funded by the VA Cooperative Studies Program. Ishani reports no disclosures.

American Heart Association (AHA) Scientific Sessions 2022. Presentation 19443. Presented November 5, 2022.

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