Generic drugmaker Endo Pharmaceuticals has insisted that it will continue to sell its generic version of Purdue Pharma’s blockbuster painkiller OxyContin, despite a legal knockback that could force it to withdraw the drug and face heavy damages.

Endo issued a defiant statement yesterday, just days after a federal appeals court in the USA overturned an earlier ruling that patents covering OxyContin (oxycodone) were unenforceable.

The appeals court remanded the case back to a district court, where a rehearing will occur.

Purdue's product had total annual sales of about $1.2 billion, although these are expected to fall off swiftly now that cheaper generics on the US market. In December, the world’s largest generics company Teva Pharmaceutical Industries, joined Endo in selling a copycat version of the drug.

Endo said last month it is expecting to add $50-$60 million to its coffers from sales of its generic OxyContin product in 2006, which would contribute about $0.20 to $0.24 per share to its predicted earnings of $1.75-$1.80 a share.

IMS Health data suggest oxycodone is the leading opioid used in the treatment of moderate-to-severe pain in the USA, with sales of nearly $2 billion for the 12-months ending August 2005.