Abstract: Seven trials involving 1558 participants were included in this review; 457 were involved in four trials of antibiotic medication, and 1101 were involved in three trials of beta-blocker medication. Five of the studies were rated at a high risk of bias. Individually, all of the included trials reported non-significant differences in AAA expansion rates between their intervention and control groups. The two major drug groups were then analysed separately. For AAA expansion it was only possible to combine two of the antibiotic trials in a meta-analysis. This demonstrated that roxithromycin had a small but significant protective effect (MD -0.86 mm; 95% confidence interval (CI) -1.57 to -0.14). When referral to AAA surgery was compared (including all four antibiotic trials in the meta-analysis), non-significantly fewer patients were referred in the intervention groups (OR 0.96; 95% CI 0.59 to 1.57) than the control groups. When only the trials reporting actual elective surgery were included in a subgroup analysis, the result remained statistically non-significant (OR 1.17; 95% CI 0.57 to 2.42). For the beta-blocker trials, when all were combined in a meta-analysis, there was a very small, non-significant protective effect for propranolol on AAA expansion (MD -0.08 mm; 95% CI -0.25 to 0.10), and non-significantly fewer patients were referred to AAA surgery in the propranolol group (OR 0.74; 95% CI 0.52 to 1.05). Bronchospasm and shortness of breath were the main adverse effects from the beta-blockers. In one trial the adverse effects were reportedly so severe that the trial was stopped early after two years. There is some limited evidence that antibiotic medication may have a slight protective effect in retarding the expansion rates of small AAAs. The quality of the evidence makes it unclear whether this translates into fewer referrals to AAA surgery, owing mainly to the small sample sizes of the studies. Antibiotics were generally well tolerated with minimal adverse effects. Propranolol was poorly tolerated by patients in all of the beta-blocker trials and demonstrated only minimal and non-significant protective effects. Further research on beta-blockers for AAA needs to consider the use of drugs other than propranolol. In general, there is surprisingly little high quality evidence on medical treatment for small AAAs, especially in relation to the use of newer beta-blockers, ACE inhibitors and statins.

Plain-language summary: We identified seven trials involving 1558 participants where the aneurysm diameters of patients randomised to receive medical treatment were compared to those participants given a control medication or surveillance imaging alone. Four trials studied the effects of antibiotics on slowing aneurysm growth, and showed a small protective effect. Three trials studied the effects of beta-blockers, and demonstrated a very small protective effect. Notably, the beta-blocker drugs were associated with a large number of adverse effects. It was unclear whether either drug type delayed referral to aneurysm surgery. The accuracy of the results was limited by the low number of participants (especially important when trying to detect small changes in aneurysm growth rates) and some potentially damaging biases.