Lay summary
Approximately 3 percent of elderly New Zealanders have an abdominal aortic aneurysm (AAA), with a greater burden amongst Māori. The widespread use of abdominal imaging means that most AAA are identified when they are small (<55mm), asymptomatic and at low risk of rupture (~1% per year). Currently, there are no medical therapies to slow AAA growth, with regular surveillance being the only management option, until the aneurysm reaches a size which warrants the risk associated with performing a surgical repair. The Metformin Aneurysm Trial (MAT) is a multi-centre, randomised, placebo-controlled trial to assess whether 1500mg of metformin/day will reduce AAA-related events among 1500 patients with small AAA. MAT is both large-scale, to allow reliable assessment of any moderate treatment effects, and streamlined, to enable rapid recruitment and low-cost follow-up while ensuring patient safety. This Australasian-led trial represents the largest AAA drug trial ever performed (4x larger than previous trials).