European Union antitrust officials have launched a formal antitrust probe against Danish drugmaker H Lundbeck A/S, alleging that the company broke rules on fair competition.

The European Commission (EC) said yesterday that it launched the probe on suspicion that the Copenhagen-based Lundbeck may have delayed the launch of a cheaper generic version of its antidepressant drug Citalopram in Europe.

In a statement, the Brussels-based EC said, ''The Commission in particular intends to investigate unilateral behavior and agreements by Lundbeck which may hinder the entry of generic Citalopram into markets in the European Economic Area."

The EC wants to find out whether Lundbeck made deals with other pharmaceutical companies to delay them selling Citalopram after Lundbeck's exclusive right to the drug it developed ran out in 2003.

Lundbeck said in a statement that it is cooperating fully with the EC and it is confident that the group has complied with all relevant national and EU competition legislation.

Citalopram, which belongs to a class of antidepressant drugs known as selective serotonin reuptake inhibitors, is one of the most widely used drugs to treat depression and anxiety.

It is sold under the name Celexa in the US and Canada and Cipramil in most of Europe. It acts by altering serotonin levels which can raise a person's mood.

Citalopram, with current annual sales of $1.6 billion, was originally developed by Lundbeck in 1989. Its patent expired in 2003, allowing other companies to legally produce generic versions.

But Lundbeck is alleged to have made deals with other pharmaceutical companies to block the entry of a cheaper generic version of the drug into the market.

Lundbeck recently released an updated formulation of Citalopram called escitalopram and acquired a new patent for it in the US.

This drug is manufactured and marketed by Forest Labs.

Escitalopram's patent was challenged by three generics companies in the UK courts, on the grounds that the drug was similar to Citalopram, whose patent had expired in 2003. Lundbeck managed to protect the patent after in won an appeal in 2008.

Lundbeck had also filed a patent lawsuit in the UK in 2003 against Lagap Pharmaceuticals Ltd, a unit of Sandoz (Novartis), which was selling a generic version of Citalopram in the UK supplied by India's Matrix Laboratories Ltd.

Since the patent expired in the same year, Lundbeck later withdrew the case.

In July, EC commissioner Neelie Kroes warned that she would investigate pharmaceutical companies, which stall generic drugs from entering the market once exclusive patents of their own drugs expire.

Her warning came after the EC discovered during a broad inquiry that many large drug makers were paying makers of generic drugs to delay launching cheaper generic version of their patent expired drugs.