Patients taking both metformin and insulin to help control their type 2 diabetes instead of insulin alone may not benefit from dual therapy, a new study claims.

Researchers from the Copenhagen Trial Unit, Steno Hospital, and the Copenhagen University Hospital agree the combination has a number of positive aspects but questioned the long term benefits for patients.

Authors of the study, published on bmj.com, say that more trials are necessary to provide firm evidence about the effectiveness of the combination, its long term risks and, in particular the risk of premature death.

The study included 2,217 patients over the age of 18 who had type 2 diabetes. It found various examples where levels of HbA1c were reduced with the combination of an oral glucose lowering drug and insulin.

Also, BMI levels and weight gain were also significantly reduced by metformin plus insulin by an average of 1.6kg.

However, a sparse number of important patient outcomes, including mortality from cardiovascular disease and other causes, have led the study’s authors to call for further research on long term risks.

Metformin is currently recommended by guidelines for patients with type 2 diabetes starting on insulin.

The CHMP has issued a positive opinion for the use of Byetta (exenatide twice-daily) as an add-on therapy to basal insulin for the treatment of type 2 diabetes in adults who have not achieved adequate glycaemic control.

The treatment, to be used with or without metformin and/or Actos (pioglitazone), demonstrated in clinical trials that it can reduce glycaemic control levels.

Christian Weyer, Senior Vice President, R&D, Amylin Pharmaceuticals, says Byetta “has potential as a complementary treatment approach for several reasons”.

The double-blind, 30-week clinical trial evaluating Byetta as an add-on therapy to insulin glargine showed that patients who may have been at risk of hypoglycaemia reduced their glargine dosage by a fifth.

Then, five weeks after randomisation, all patients had insulin doses titrated to achieve target fasting glucose levels. After the full 30 weeks of treatment, Byetta demonstrated a statistically significant reduction in hypoglycaemia compared to placebo, lowering levels by 1.7% from a baseline of 8.3%.

“Byetta is given in a fixed-dose regimen,” said Christian Weyer. “Its effects contribute to improved glycaemic control after meals, complementing the control of fasting blood sugar achieved with basal insulin. And in a clinical study, patients using Byetta with insulin glargine achieved better glycaemic control, without weight gain or an increased risk of hypoglycaemia, than patients using insulin glargine without Byetta.”

The injection was the first glucagon-like peptide-1 (GLP-1) receptor agonist to be approved by the FDA for the treatment of type 2 diabetes.

In November last year, Amylin and Eli Lilly announced they had amicably terminated their decade-long collaboration on the treatment.