Protocol for the Metformin Aneurysm Trial (MAT): A placebo-controlled randomised trial testing whether metformin reduces the risk of serious complications of abdominal aortic aneurysm

Golledge, Jonathan, Arnott, Clare, Moxon, Joseph, Monaghan, Helen, Norman, Richard, Morris, Dylan, Li, Qiang, Jones, Greg, Roake, Justin, Bown, Matt, and Neal, Bruce (2021) Protocol for the Metformin Aneurysm Trial (MAT): A placebo-controlled randomised trial testing whether metformin reduces the risk of serious complications of abdominal aortic aneurysm. Trials, 22. 962.

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Background: Multiple observational studies have associated metformin prescription with reduced progression of abdominal aortic aneurysm (AAA). The Metformin Aneurysm Trial (MAT) will test whether metformin reduces the risk of AAA rupture-related mortality or requirement for AAA surgery (AAA events) in people with asymptomatic aneurysms.

Methods: MAT is an international, multi-centre, prospective, parallel-group, randomised, placebo-controlled trial. Participants must have an asymptomatic AAA measuring at least 35 mm in maximum diameter, no diabetes, no contraindication to metformin and no current plans for surgical repair. The double-blind period is preceded by a 6-week, single-blind, active run-in phase in which all potential participants receive metformin. Only patients tolerating metformin by taking at least 80% of allocated medication will enter the trial and be randomised to 1500 mg of metformin XR or an identical placebo. The primary outcome is the proportion of AAA events defined as rupture-related mortality or need for surgical repair. Secondary outcomes include AAA growth, major adverse cardiovascular events and health-related quality of life. In order to test if metformin reduced the risk of AAA events by at least 25%, 616 primary outcome events will be required (power 90%, alpha 0.05).

Discussion: Currently, there is no drug therapy for AAA. Past trials have found no convincing evidence of the benefit of multiple blood pressure lowering, antibiotics, a mast cell inhibitor, an anti-platelet drug and a lipid-lowering medication on AAA growth. MAT is one of a number of trials now ongoing testing metformin for AAA. MAT, unlike these other trials, is designed to test the effect of metformin on AAA events. The international collaboration needed for MAT will be challenging to achieve given the current COVID-19 pandemic. If this challenge can be overcome, MAT will represent a trial unique within the AAA field in its large size and design.

Item ID: 71049
Item Type: Article (Scholarly Work)
ISSN: 1745-6215
Keywords: Abdominal aortic aneurysm, Metformin, Randomised controlled trial, Placebo
Copyright Information: This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data
Date Deposited: 17 Feb 2022 01:57
FoR Codes: 32 BIOMEDICAL AND CLINICAL SCIENCES > 3201 Cardiovascular medicine and haematology > 320101 Cardiology (incl. cardiovascular diseases) @ 100%
SEO Codes: 20 HEALTH > 2001 Clinical health > 200102 Efficacy of medications @ 100%
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