Omaha, NE—With past research suggesting that some antibiotics can reduce inflammation that contributes to aneurysm growth, clinicians sometimes prescribe doxycycline in hopes of putting off surgery in higher-risk patients with abdominal aortic aneurysms.

A new JAMA study might end that practice.

University of Nebraska–led researchers found that patients with the condition fared no better taking the antibiotic for 2 years than those using a placebo.

Abdominal aortic aneurysm affects about 3% of older Americans, usually male smokers. While small aneurysms frequently cause no symptoms and are often detected when an abdominal ultrasound or CT scan is performed for other reasons, larger ones can burst and create dangerous internal bleeding.

In the parallel, two-group, randomized clinical trial that was conducted at 22 U.S. medical centers between May 2013 and January 2017, the focus was on patients aged 50 years or older with small (3.5-5.0 cm for men, 3.5-4.5 cm for women) infrarenal aneurysms. The final date of follow-up for the 261 randomized patients was July 31, 2018.

Participants received either 100 mg of oral doxycycline capsules or 100 mg orally or placebo twice daily for 2 years. Defined as the primary outcome was any change in abdominal aortic aneurysm maximum transverse diameter, as determined by CT images at baseline and follow-up at 2 years. Patients were assigned ranks based on the maximum transverse diameter (measured or imputed) of the aorta and also if they underwent aneurysm repair or died. To facilitate the primary analysis, those ranks were converted to scores having a normal distribution.

The final analysis set included 129 patients assigned to doxycycline and 125 to placebo; those participants had a mean age of 71 years and most, 86% were men. The outcome normal scores used in the primary analysis were based on maximum transverse diameter (measured or imputed) in 113 patients (88%) in the doxycycline group and 112 patients (90%) in the placebo group; aneurysm repair in 13 (10%) and 9 (7%), and death in 3 (2%) and 4 (3%), respectively.

Researchers report that the primary outcome, normal scores reflecting change in aortic diameter, did not differ significantly between the two groups, mean change in normal scores, 0.0262 versus −0.0258 (1-sided P = .71). The study determined that mean (SD) baseline maximum transverse diameter was 4.3 cm (0.4 cm) for doxycycline and 4.3 cm (0.4 cm) for placebo.

At the 2-year follow-up, the change in measured maximum transverse diameter was 0.36 cm (95% CI, 0.31 to 0.40 cm) for 96 patients in the doxycycline group versus 0.36 cm (95% CI, 0.30 to 0.41 cm) for 101 patients in the placebo group (difference, 0.0; 95% CI, −0.07 to 0.07 cm; 2-sided P = .93).

“Among patients with small infrarenal abdominal aortic aneurysms, doxycycline compared with placebo did not significantly reduce aneurysm growth at 2 years,” the authors conclude. “These findings do not support the use of doxycycline for reducing the growth of small abdominal aortic aneurysms.”

Coauthor John Curci, MD, associate professor in the Division of Vascular Surgery at Vanderbilt University School of Medicine in Nashville, Tennessee, noted, “Taking doxycycline to prevent or slow the growth of small abdominal aortic aneurysms is not advised or helpful, even though it reduced circulating markers of inflammation.”

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