This is a plain English summary of an original research article
Taking a glucagon-like peptide-1 receptor (GLP-1) agonist drug lowers the likelihood of having a stroke, heart attack or dying due to cardiovascular causes by 12%. The drugs give a similar 12% reduction in overall mortality. They do not increase the risk of heart failure, very low blood sugar levels or pancreatic disease.
Diabetes causes one in five strokes along with other cardiovascular complications. Clinicians aim to reduce these risks and lower blood sugar levels. This meta-analysis is the first to combine data on cardiovascular outcomes from seven large trials of the GLP-1 agonists, including over 56,000 participants. Most trial participants had established heart disease.
These findings suggest that GLP-1 agonists are an effective and safe treatment option for people with diabetes and co-existing heart disease. However, these drugs are expensive, and cost-effectiveness evidence is needed for the NHS.
Why was this study needed?
About 4.7 million people (about 7% of the population) in the UK have diabetes, of which 90% is type 2 diabetes. High blood sugar levels can damage the heart and blood vessels. Every week, this condition results in around 700 strokes, 500 heart attacks and 2,000 cases of heart failure. The NHS spends about £10 billion a year (10% of its budget) budget on treating diabetes and its complications.
GLP-1 agonists are one of two types of sugar-lowering drugs that reduce sugar levels and have positive cardiovascular effects. Trials of individual GLP-1 drugs have involved different patient populations and had mixed findings.
This systematic review aimed to combine the results of several trials and to update the evidence base for the cardiovascular impact of GLP-1 drugs. This is the first review to incorporate new trials of dulaglutide and oral semaglutide, published in summer 2019.
What did this study do?
In this meta-analysis, the researchers combined results from seven trials in which patients with type 2 diabetes were randomised to receive either a GLP-1 agonist or a placebo, in addition to any other medications prescribed. In six of these trials, the GLP-1 drug was administered by daily or weekly injection.
The review included published trials with cardiovascular outcomes and more than 500 participants. In all but one of these trials, over 70% of participants had established cardiovascular disease. The remaining participants had cardiovascular risk factors. Patients were followed-up for between one and five years.
All the trials were assessed as high quality and so we can have confidence in these results.
What did it find?
- Around 75 people would need to take a GLP-1 receptor agonist to prevent one serious cardiovascular event (heart attack, stroke, or death due to cardiovascular causes) over an average (median) follow-up period of 3.2 years (number needed to treat [NNT] 75, 95% confidence interval [CI] 50 to 151; hazard ratio [HR] 0.88, 95% CI 0.82 to 0.94; 7 trials, 56,004 participants).
- Subgroup analyses show no clear difference in the rate of these cardiovascular events according to established cardiovascular disease, baseline blood sugar level, kidney function, duration of follow-up, daily or weekly drugs, BMI or age.
- Around 108 people would need to take the drug to prevent one death from any cause over 3.2 years (NNT 108, 95% CI 77 to 260; HR 0.88, 95% CI 0.83 to 0.95; 7 trials, 56,004 participants).
- Compared with placebo, taking a GLP-1 receptor agonist has a very small effect on the risk of hospital admission for heart failure. This is a marginally statistically significant result, with 312 patients needing to take the drug for each admission prevented over 3.2 years (NNT 312, 95% CI 165 to 2,810; HR 0.91, 95% CI 0.83 to 0.99; 7 trials, 56,004 participants).
- The drug does not cause any increased risk of severe low blood sugar, inflammation of the pancreas or pancreatic cancer, compared with placebo.
What does current guidance say on this issue?
NICE’s 2015 guideline on type 2 diabetes recommends that GLP-1 agonists are used as a second-order drug for weight reduction. It does not include recommendations for these drugs in relation to cardiovascular outcomes and predates the GLP-1 cardiovascular trials.
Guidance published jointly by the European Association for the Study of Diabetes and the American Diabetes Association (2018) recommends an individualised approach to treatment incorporating patient risk factors and co-existing conditions. For patients with established cardiovascular disease and poor control of blood sugar, a proven GLP-1 receptor agonist or an SGLT2 inhibitor can be added to metformin.
What are the implications?
A 2019 NICE surveillance report proposes that a new NICE diabetes guideline will include a cost-effectiveness analysis of GLP-1 receptor agonists and other anti-diabetic drugs. The average annual cost of GLP-1 drugs varies between £700 and £1,500 annually.
This meta-analysis did not include sufficient patients without cardiovascular disease to establish whether GLP-1 drugs are effective for primary prevention in lower-risk patients.
Longer-term trials are needed as people with diabetes are likely to require treatment for longer than five years.
Citation and Funding
Kristensen S, Rorth R, Jhund P et al. Cardiovascular, mortality, and kidney outcomes with GLP-1 receptor agonists in patients with type 2 diabetes: a systematic review and meta-analysis of cardiovascular outcome trials. Lancet Diabetes Endocrinol. 2019;7(10):776-85.
This project received no specific funding.
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NICE. 2019 surveillance of diabetes (NICE guidelines NG17, NG18, NG19 and NG28). London: National Institute for Health and Care Excellence; 2019.
Standl E. GLP-1 receptor agonists and cardiovascular outcomes: an updated synthesis. Lancet Diabetes Endocrinol. 2019;7(10):741-43.
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