After use of GlaxoSmithKline's Avandia was severely restricted by the US Food and Drug Administration last month, and suspended in Europe, analysts at Datamonitor have polled doctors across the pond to find out about prescribing habits for diabetes.

The market research agency carried out in-depth interviews with 45 primary care physicians and 23 specialist endocrinologists/diabetologists  who prescribe Avandia (rosiglitazone) to see if they will change medication, and to which therapies these patients could be switched. It is clear that US sales of the drug will plummet due to safety concerns and FDA restrictions, but Datamonitor predicts a small number of patients will remain on Avandia because they cannot tolerate other therapies.

The survey also notes that there is no single strategy preferred by doctors moving Avandia patients to alternative therapies "and this provides an opportunity for multiple antidiabetic drugs to gain market share". While many patients will switch within the glitazone class to Takeda’s Actos (pioglitazone), the Japanese firm has "only a limited opportunity to capitalise on its competitor’s fall" before Actos loses patent protection from 2011.

Datamonitor notes that other patients will switch to the dipeptidyl-peptidase 4 (DPP-4) inhibitor class, particularly Merck & Co’s blockbuster class leader Januvia (sitagliptin). The DPP-4 inhibitors are less effective at lowering blood sugar but have a benign safety profile and fewer side effects than the glitazones.

Injectable glucagon-like peptide-1 (GLP-1) agonists, ie Eli Lilly/Amylin's Byetta (exenatide) and Novo Nordisk's Victoza (liraglutide) will also gain some patients, the report claims, and this will "further drive the growth of the class before the arrival of longer acting once-weekly drugs in the pipeline". Some patients will also be switched from Avandia to the once-daily basal insulins Lantus (insulin glargine) from Sanofi-Aventis and Novo's Levemir (insulin detemir).

Datamonitor concludes by predicting that GSK will suffer Avandia  losses of over $1.2 billion in the USA and the five major European markets (France, Germany, Italy, Spain and the UK) from 2010 to 2012. However, over the same period, the antidiabetics market as a whole will grow by over $200 million.