Wilmington, Delaware: A unit of GlaxoSmithKline Plc, the UK’s largest drugmaker, joined with Canadian business partner Apotex Inc. to sue Indian generic pharmaceutical firm Lupin Ltd over plans to market copies of the antidepressant Paxil.

SmithKline Beecham Ltd claims Lupin is infringing a US patent for Paxil and should pay damages if the generic product is brought to market, according to a complaint filed Monday in federal court in Wilmington, Delaware.

Lupin is making “substantial preparation in the US" to sell the copies, which indicates “a refusal to change the course of their actions," according to the complaint. Bloomberg