A new study reveals there is no benefit to asking abdominal aortic aneurysm patients to delay surgery while they attempt to reduce inflammation through antibiotic use.1

If a patient’s aneurysm could grow too large, surgery is the chief option. “Doxycycline, an old antibiotic, has the ability to block enzymes that break down tissue,” says Tim Baxter, MD, a vascular surgeon and professor of surgery at the University of Nebraska Medical Center. “There has been a lot of interest in the possibility that doxycycline would keep aneurysms from growing ... animal studies showed good results. One small clinical trial had good results, too, suggesting this treatment could keep people from having surgery.”

To see if these results would hold up in a randomized, clinical trial, Baxter and colleagues enrolled patients, age 50 years and older, from 22 U.S. clinical centers between May 2013 and January 2017.

All patients had small infrarenal aneurysms. A total of 133 patients were assigned doxycycline and 128 were assigned to placebo. “We thought this drug could work. It doesn’t have a huge number of side effects, and it’s not expensive — or at least it wasn’t when we started the trial,” Baxter explains. Researchers collected blood work and performed a CT scan every six months for a two-year period. The aneurysms were small enough that physicians would observe them to see if they would grow.

If the antibiotic worked, then researchers would expect to see slower growth among patients who received doxycycline than among the placebo cohort.

The results were surprising: Baxter and colleagues observed no significant difference in the change in aortic diameter between the doxycycline group and the placebo group. Deaths were similar in the two groups.

“In a primary analysis of how much change occurred between the size of the aneurysm at enrollment and the size at two months, we found that the placebo group and doxycycline group grew at exactly the same rate,” Baxter says. “It didn’t do anything.” Researchers also were surprised to see that doxycycline alleviated inflammation, even if the drug did not affect the aneurysm, he adds.

After two years, 13 doxycycline patients and nine placebo patients underwent an aneurysm repair procedure. Three people in the doxycycline group and four in the placebo group died.

Patients with an abdominal aortic aneurysm that might require surgery should be told there is no treatment to slow the growth of their aneurysm, Baxter says. “If they continue to smoke, the aneurysm will grow a little bit faster, so we encourage them to stop smoking,” he says. “Then, we tell them that we’ll watch it, and at the [small] size it is, the risk of a rupture is very small.” Aneurysm repair surgery can occur in a 23-hour stay, Baxter notes.

From a patient perspective, the good news is the aneurysms were growing slower than expected, based on historical data, Baxter notes.

“It’s possible the measurements in the past were inaccurate, or something else we’re doing is making them grow slower,” he offers. “That’s good news for patients because it means it’s more likely that they won’t have to have their aneurysm fixed.”


  1. Baxter BT, Matsumura J, Curci JA, et al. Effect of doxycycline on aneurysm growth among patients with small infrarenal abdominal aortic aneurysms. JAMA 2020;323:2029-2038.