Many people with type 1 diabetes have suboptimal glucose control and features of type 2 diabetes (so-called ‘double diabetes’). This has led to interest in adjunctive therapy with noninsulin glucose control agents such as metformin. Clinical trials show some benefits of metformin in people with type 1 diabetes. Its (off-label) use merits discussion with the person with diabetes and their multidisciplinary team.
- People with type 1 diabetes may also have insulin resistance and clinical features of type 2 diabetes, contributing to suboptimal glucose control, micro- and macrovascular complications and premature death.
- There is interest in use of adjunctive medications for glucose control in people with type 1 diabetes treated with insulin; however, no medications are currently approved for this use in Australia.
- Among potential adjunctive medications, metformin has the largest evidence base and has small benefits for HbA1c, weight, LDL cholesterol, vascular function, carotid intima media thickness and kidney function in people with type 1 diabetes.
- Potential risks of adjunctive metformin include gastrointestinal upset, decreased vitamin B12 levels and possibly an increased risk of lactic acidosis.
- The optimal criteria for adjunctive metformin use in people with type 1 diabetes and monitoring are currently uncertain.
- Off-label use of adjunctive metformin in people with type 1 diabetes should be agreed with, and monitored by, the person with diabetes and their endocrinologist, GP and diabetes educator.