Indian drugmaker Dr Reddy's Laboratories Ltd said on Wednesday it has filed with the US Food and Drug Administration to market a generic version of Aventis Pharmaceuticals' anti-allergy drug Allegra.

Aventis' brand, which is one of its blockbuster drugs, had annual sales of about $1.35 billion in the United States, the Hyderabad-based Dr Reddy's said in a statement.

It said it had notified Aventis of the filing of the Abbreviated New Drug Application (ANDA) for Fexofenadine HCl tablets, equivalent to 30 mg, 60 mg and 180 mg forms of Allegra.

Dr Reddy's said it had filed the ANDAs with Paragraph IV certifications on all seven Orange Book patents listed for the Allegra tablets. The patents are due to expire between May 2012 and November 2013.

The Orange Book lists patents from branded drugmakers other than that for the original chemical.

Under this filing, if Dr Reddy's succeeds in getting approval, it will have an initial exclusive right among generic drugmakers to market the drug for six months along with Aventis.

Aventis has filed a lawsuit against Dr Reddy's in the District Court of New Jersey alleging infringement on six Orange Book patents, the statement said.

"A final decision on this is a long way off, but if Dr Reddy's manages to get the approval, it will mean a huge upside," said an analyst with a foreign brokerage.

Dr Reddy's shares were up 0.76 per cent at Rs 907 at the Bombay Stock Exchange in morning deals while the benchmark exchange index was up 0.77 per cent.