Use of doxycycline to decrease the growth rate of abdominal aortic aneurysms: A randomized, double-blind, placebo-controlled pilot study

Objective: Eradication of Chlamydia pneumoniae infection and inhibition of elastolytic matrix metalloproteinases with doxycycline have been suggested to reduce the growth rates of small abdominal aortic aneurysms (AAA). We de signed a study to investigate the efficacy of doxycycline in reducing the e xpansion of small AAAs. Subjects and Methods: This was a prospective, double-blind, randomized, pla cebo-controlled study that was set in a university referral hospital. The s tudy group consisted of 32 of 34 initially eligible patients who had ail AA A diameter perpendicular to the aortic axis of 30 mm or more in size or a r atio of infrarenal to suprarenal aortic diameter of 1.2 or more and a diame ter less than 55 mm. Patients were randomly assigned to receive either doxy cycline (150 mg daily) or placebo during a 3-month period and underwent ult rasound surveillance during an 18-month period. Outcome measures included a neurysm expansion rates, the number of patients who had AAA rupture or repa ir, C pneumoniae antibody titers, and serum concentrations of C-reactive pr otein. Results: The aneurysm expansion rate in the doxycycline group was significa ntly lower than that in the placebo group during the 6- to 12-month (P =.01 ) and the 12- to 18-month periods (P =.01). Five patients (41%) in the plac ebo group and I patient (7%) in the doxycycline group had an overall expans ion of the aneurysm of 5 mm or more during the 18-month follow-up. Among th e placebo group patients, a higher expansion rate was observed in those wit h enhanced C pneumoniae immunoglobulin G antibody titers (> 128) than in th ose with lower titers (P =.03). Doxycycline treatment had no clear effect o n antibody titers. However, at 6-month follow-up, C-reactive protein levels in the doxycycline group were significantly lower than the baseline levels (P =.01). Conclusions. The results of this small pilot study suggest that doxycycline may favorably alter the outcome of patients with small AAA. However, becau se of the small size of this randomized study and of the potentially confou nding effect of pretreatment risk factors, doxycycline -based treatment can not be justified only on the ground of the current results. Because of the high prevalence of this disorder and its clinical, social, and economic rel evance, a multicenter study should be performed to further investigate whet her there is any place for medical treatment of small AAAs.