Boehringer Ingelheim and Eli Lilly have started a Phase III trial designed to show their diabetes drug Trajenta is safe and effective in patients with signs of kidney damage.

The move comes as Trajenta (linagliptin) is jostling for market share in the dipeptidyl peptidase-4 (DPP-4) inhibitor class with the likes of AstraZeneca and Bristol-Myers Squibb's Onglyza (saxagliptin) and Merck & Co's sector-leading Januvia (sitagliptin).

Boehringer and Lilly are keen to show that Trajenta has properties that make it a good candidate for the treatment of type 2 diabetics who are starting to excrete albumin in their urine, an indicator of diabetic kidney disease.

Chronic kidney disease affects more than 40% of adults with diabetes, and tends to occur despite improvements in glycaemic control.

The Phase III study - called MARLINA - will enrol type 2 diabetics with prevalent albuminuria and a urinary albumin-to-creatinine (UACR) ratio of 30-3000mg/g creatinine who are already receiving treatment for diabetic nephropathy, said the pharma companies.

"With linagliptin, no dose adjustment is required even for patients with declining renal function," said Prof. Per-Henrik Groop, of Helsinki University Central Hospital in Finland, who is MARLINA's principal investigator.

The primary endpoint of MARLINA is the change from baseline in glycated haemoglobin (HbA1c) - a long-term measure of glycaemic control - after 24 weeks of treatment. The study is expected to complete in 2014.

Last year, a meta-analysis of 13 late-stage linagliptin studies found that patients were 16% less likely to develop symptoms of kidney disease compared to placebo, even when the diabetics were already being treated with ACE inhibitors or angiotensin receptor blockers antihypertensive drugs that are often prescribed to diabetics to help protect the kidneys.

It remains to be seen however whether the proposed renoprotective effect is peculiar to linagliptin or common to all DPP4 inhibitors.

"The initiation of this new trial reinforces our ongoing commitment to the field of type 2 diabetes," said Prof Klaus Dugi, corporate senior vice president, medicine, at Boehringer. "It is important to find more treatment options, especially for those patients who are at risk of renal and cardiovascular disease and who have limited choices of treatment."