Lilly has filed for approval of a new indication for its strongest-growing drug, Cymbalta, in the treatment of generalised anxiety disorder.

Cymbalta (duloxetine HCl) is already approved to treat depression and neuropathic pain, and saw sales surge 118% in the first quarter of this year to $233 million, and is tipped to be the next flagship product at the company now that schizophrenia drug Zyprexa (olanzapine), which makes up almost a third of overall sales and about half of Lilly’s profit, is starting to show its age.

Zyprexa is under assault in the increasingly crowded schizophrenia segment, and saw its first-quarter sales dip 3% to $1 billion on the back of increased competition from the likes of Johnson & Johnson’s Risperdal (risperidone), AstraZeneca’s Seroquel (quetiapine), Pfizer’s Geodon (ziprasidone) and Bristol-Myers Squibb’s Abilify (aripiprazole). Pressure on the drug could also be exacerbated by generic competition to Risperdal in the USA next year.

Meanwhile, Lilly is having to defend Zyprexa from thousands of lawsuits brought by people who claim the drug contributed to the development of their diabetes.

Lilly estimates that about four million people in the USA suffer from generalised anxiety disorder, which the National Institute of Mental Health defines as chronic anxiety and exaggerated worry and tension with little or no provocation. So approval of Cymbalta in this indication represents a significant increase in the population of patients that could be eligible to receive the drug.

Meanwhile, Lilly said it is also testing Cymbalta in Phase III studies as a potential therapy for fibromyalgia, a chronic pain disorder characterised by muscle aches, muscle pain and stiffness, fatigue and sleep disturbance.