Study designs of evaluations included in the review
No inclusion criteria were given for the study design, with the exception that case reports were eligible if CHF was the only contraindication to metformin use. Retrospective cohort studies and prospective randomised studies were included. The duration of follow-up ranged from 1 to 4 years.
Specific interventions included in the review
Studies assessing metformin were eligible for inclusion. The comparators in the included studies included thiazolidinedione (TZD), insulin and sulfonylurea. One study included a group taking metformin and sulfonylurea combined therapy. One study compared continuation of metformin therapy with discontinuation of metformin therapy. The participants were also taking other drugs for heart failure.
Participants included in the review
Studies of people with type 2 diabetes and congestive heart failure (CHF) were sought. The participants in the included studies were people with CHF and diabetes, patients recently discharged from hospital with CHF and diabetes, and users of metformin with an elevated serum creatinine between 1.5 and 2.5 mg/dL and coronary artery disease, CHF or chronic obstructive pulmonary disease. One study excluded people who had been hospitalised for CHF in the previous 3 years. One study excluded participants younger than 65 years; in the other studies the mean ages ranged from 64 to 72 years.
Outcomes assessed in the review
Studies that reported clinical outcomes were eligible for inclusion. The outcomes reported were incidence of lactic acidosis, mortality, rate of myocardial infarction or cardiovascular events, and hospital readmission rates.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.