Can Metformin Prevent Asthma Attacks? Cochrane Review Plan Aims to Find Out
A new Cochrane protocol will systematically test whether the diabetes drug metformin lowers asthma exacerbations in adults. No results exist yet.
Summary
This is a Cochrane review protocol, not a results paper. It sets out how researchers will evaluate whether metformin, a common oral diabetes drug, reduces asthma exacerbations in adults. Animal studies and observational data hint at protective effects, including fewer emergency visits and hospitalisations, possibly via improved insulin sensitivity and anti-inflammatory action. The team will search major databases and trial registries and include randomised trials and non-randomised studies. They will assess bias with RoB 2 and ROBINS-I and rate certainty with GRADE. Critical outcomes are exacerbations, steroid courses, hospitalisations and ED visits. Safety will also be examined. No findings are reported yet, so metformin should not be used for asthma on the basis of this paper.
Detailed Summary
Asthma affects nearly 300 million people worldwide, and exacerbations drive much of its illness, death and inequity. Current treatment relies mainly on inhaled corticosteroids and bronchodilators, which have side effects and are disliked by some patients, such as children. Oral options are limited. Poor glycaemic control and insulin resistance have been linked to worse asthma outcomes independent of obesity, which raises the question of whether metformin might help.
This paper is a protocol, meaning it describes the planned review and reports no results. The review will assess metformin's effects on exacerbations in adults (18+) with asthma on maintenance treatment. Adults with COPD or bronchiectasis will be excluded because metformin may act differently there. Metformin for any indication (type 2 diabetes, obesity, PCOS) will be compared with placebo or no metformin, with co-interventions matched between groups. The authors will extract dose and duration.
The team will search the Cochrane Airways Trials Register, MEDLINE, Embase, Web of Science, ClinicalTrials.gov and the WHO ICTRP, with no language or date limits. They expect few randomised trials because metformin is off-label for asthma, so non-randomised studies of interventions will also be included. Uncontrolled designs, cross-sectional studies and standalone qualitative work will be excluded. Two reviewers will screen, extract data and assess bias independently, using RoB 2 for trials and ROBINS-I for non-randomised studies, with GRADE for certainty. Key confounders to capture include age, sex, BMI, smoking, asthma severity, comorbidities, HbA1c and baseline treatments.
Critical outcomes follow coreASTHMA recommendations: symptom or lung-function deterioration with more rescue use, exacerbations needing systemic steroids for at least three days, hospitalisation, and ED visits. Important outcomes are asthma control (ACT, ACQ), quality of life (AQLQ), and serious and minor adverse events such as lactic acidosis, pancreatitis and gastrointestinal effects. Effects will be expressed as risk ratios, hazard ratios, rate ratios or mean differences, pooled only when studies are sufficiently similar, using random-effects models.
If the evidence is promising, it could inform future trials and guide prescribing for people with asthma who also need metformin, particularly in groups with higher burdens of both asthma and metabolic disease. Caveats: no data yet, likely reliance on observational studies prone to confounding, and no evidence yet to support metformin as an asthma therapy.
Key Findings
- This is a protocol; no efficacy or safety results are reported yet.
- Observational studies suggest metformin users have fewer asthma exacerbations, ED visits and hospitalisations, but causality is unproven.
- Review will include RCTs and non-randomised studies because off-label RCTs of metformin for asthma are expected to be scarce.
- Adults with COPD or bronchiectasis will be excluded to avoid confounding from differing metformin effects.
- Critical outcomes include steroid-requiring exacerbations, hospitalisations and ED visits, with safety assessed as an exploratory outcome.
Methodology
Cochrane intervention review protocol following MECIR and PRISMA 2020. It plans searches of four databases and two trial registries, duplicate screening and extraction, RoB 2 and ROBINS-I bias assessment, GRADE certainty rating, and random-effects meta-analysis where studies are comparable.
Study Limitations
As a protocol, it provides no outcome data. The planned inclusion of non-randomised studies means findings may be affected by confounding and indication bias, and few or no RCTs are expected. Restriction to adults without other respiratory disease limits generalisability.
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