Metformin is widely used as a first line treatment for type 2 diabetes and it is usually continued when treatment is intensified, such as with other oral agents or by insulin therapy. This systematic review looked at whether metformin is actually beneficial to patients who are using insulin.
In people with type 2 diabetes, does treatment with metformin plus insulin as compared with insulin treatment alone lead to reduced mortality?
The reviewers looked at outcomes data for overall mortality and cardiovascular mortality. Secondary outcomes included rates of complications, adverse events and glyaemic control.
The reviewers extracted and analysed data from 23 trials, comprising 2,117 participants.
For the primary outcomes there was so much uncertainty about the estimates of benefit that there is no benefit in reporting them. This was due to the very low event rates in the trials.
However, glycaemic control, as measured by HbA1c, was significantly better with metformin and insulin when compared with insulin alone. The mean difference was 0.60% (95% confidence interval −0.89% to −0.31%).
Users of this research should consider:
- The reviewers carried out a comprehensive search and rigorous evaluation of study quality.
- They concluded that the trials in this area were of low methodological quality.
- Patient-important outcomes were not well reported. Many of the studies were too short for them to manifest themselves.
- It seems likely that there would be important clinical heterogeneity between the studies.
- We need higher quality, longer term studies in this area that focus on outcomes that are relevant to patients.
The full text of this paper is available from the BMJ:
Hemmingsen B, Christensen LL, Wetterslev J, Vaag A, Gluud C, Lund SS, Almdal T. Comparison of metformin and insulin versus insulin alone for type 2 diabetes: systematic review of randomised clinical trials with meta-analyses and trial sequential analyses. BMJ. 2012 Apr 19;344:e1771. doi: 10.1136/bmj.e1771.