Sales of drugs to treat type 2 diabetes in seven major markets are set to nearly double by 2020, reaching almost $45 billion from 2010's total of $23.4 billion, according to new forecasts.

Market growth in the US, UK, France, Germany, Italy, Spain and Japan will be driven by a steady increase in these countries' drug-treated patient populations and an extensive pipeline of products that are expected to launch between now and 2020, says the report, from Decision Resources.

The biggest growth in market share of all types of drugs used to treat type 2 diabetes will be seen for the dipeptidyl peptidase (DPP)-IV inhibitors and glucagon-like peptide (GLP)-1 analogues, whose combined market share in these seven markets will increase from 20% last year to 47% by 2020, it adds.

Merck & Co's Januvia (sitagliptin), which currently dominates the DPP-IV inhibitor class, will consolidate this leading position, while other DPP-IV inhibitors will struggle because of their lack of clinical advantages over Januvia, according to Decision Resources.

Turning to the GLP-1 analogues, the report notes that these products have a strong efficacy profile and elicit weight loss, and that they are very popular among thought leaders, who view improved glycaemia, weight loss and preservation of beta-cell function in obese type 2 diabetics as landmark progress.

The US launch of Eli Lilly/Amylin/Alkermes' once-weekly GLP-1 analogue Bydureon (exenatide prolonged-release suspension for injection) has been delayed for up to 18 months, and this gives Novo Nordisk's once-daily GLP-1 analogue Victoza (liraglutide) the chance to capitalise on its strong initial uptake, it adds.

Moreover, the decision by the US Food and Drug Administration (FDA) to restrict the availability of GlaxoSmithKline's Avandia (rosiglitazone) in the US and a ruling by the European Medicines Agency (EMA) to withdraw the drug in Europe will cause the product to lose almost all its sales, leaving Takeda's Actos (pioglitazone) as the predominant representative of the peroxisome proliferator-activated receptor (PPAR)-gamma agonist drug class on the market.

However, the report also notes that concerns about a possible link between Actos and bladder cancer emerged during the first half of this year.

"These concerns led to Actos begin withdrawn in France and Germany and will contribute to a decline in sales in other markets - a decline that will be compounded by the entry of generic Actos, beginning towards the end of 2011," according  to Christine Helliwell, an analyst at Decision Resources.

"These safety concerns and generic erosion will lead to a reduction in market share for the PPAR-gamma agonists from 24% in 2010 to just 3% in 2020," Dr Hellliwell forecasts.