Pfizer Inc has filed patent infringement suits against three Indian drug manufacturers - Sun Pharma, Lupin Ltd and Wockhardt Ltd to block the companies from marketing generic equivalents to its blockbuster pain management drug, Lyrica in US.

Pfizer's Lyrica, which was launched in the US in 2005 for the management of neuropathic pain went on to become a top selling medicine for central nervous system disorders with global sales of $2.5 billion in 2008. In the US, the drug yielded revenues of $1.45 billion in 2008.

Lyrica is prescribed for the treatment of epilepsy, and diabetic neuropathy pain and is available in India and all markets globally.

According to market research analysis, the product is expected to notch up almost $3 billion in sales by 2017, out of the 6.3 billion neuropathic pain drug market by the time.

Additionally, the company has since the launch of the drug identified several new areas for the drug's use including management of co-morbid conditions like sleep disturbance, anxiety and depression.

According to the company, which launched Lyrica in India in the first quarter of 2006, the product is the first pregabalin molecule to be approved by Indian regulatory authorities, based on results of clinical trials conducted in India and abroad. In the Indian markets, the company's products 'Caduet' and 'Lyrica' (both launched in February 2006) have, between them, contributed around 1 per cent in sales of to Pfizer India's pharma revenues.

US rules for the sale of generic drugs, after the expiry of patent protection to the original manufacturer, allow the first-to-file to challenge the patent of the innovator drug 180 days of marketing exclusivity for 180 days following the patent expiry.

The innovator has to sue the generic company within 45 days of the challenge to get a 30-month stay on final marketing approval.

Other companies against which Pfizer has initiated action include Teva, Sandoz, Actavis, Cobalt Laboratories, Alphapharm Pty Ltd for Lyrica patent violations in US.

Pfizer was founded in 1849 and is the world's largest company in terms of drug sales. The company makes several top selling drugs including Liptor used to lower blood cholesterol, Lyrica, the neuropathic pain/fibromyalgia drug, Diflucan, the oral antifungal medication, Zithromax, a long-acting antibiotic, Viagra, the well-known drug for treating erectile dysfunction and the anti inflammatory, Celebrex.