Global pharma major GlaxoSmithKline's [Get Quote] strategy of launching an improved version of the migraine drug, Imitrex, after having an out-of-court settlement with Dr Reddy's and Ranbaxy Laboratories [Get Quote] over its copycat version's launch in the US may limit the two Indian firms' financial gains. These two were the first to challenge the patent on this drug.

GSK [Get Quote] has already launched an improved version of the migraine drug, Trexima and is switching patients using Imitrex to the new drug. Other generics companies such as Cobalt Pharmaceuticals and Mylan Laboratories are also waiting to launch their products after final approval.

As per the US rules for selling generics drugs, the first to challenge an innovator patent gets 180 days of exclusive sales in the US market upon patent expiry. Of late, innovator companies assign or launch own authorised generic versions to protect their sales during patent expiry and to reduce the upside the exclusivity holder gets from 180 days of sales.   

Experts believe Ranbaxy and Dr Reddy's may not enjoy a large upside from Imitrex, a drug that had annual sales of $878 million (around Rs 4,390 crore or Rs 43.90 billion) as of March 31, 2006, in the US. They estimate Dr Reddy's may not get more than $8-$15 million sales in 2009 since majority of sales revenue has to be given to GSK, for allowing the launch the authorised generic version. 

"Neither Ranbaxy nor Dr Reddy's so far have commented on the upside they may get from Imitrex," said an industry analyst.  

The battle between Dr Reddy's and Ranbaxy over Imitrex (sumatriptan succinate tablets) is one of the first instances in which an authorised generic drug reaches the market before the first to file generic drug gets regulatory clearance in the history of drug patent litigations happening in the US, said experts.

They are also surprised why Ranbaxy, the first to challenge the Imitrex patent, is not getting final approval for its version from the USFDA, though it was given tentative approval almost three years ago.