Mylan Laboratories says that a US court has blocked the Food and Drug Administration from approving competing generic versions of Pfizer's Norvasc until April 13.

The FDA was due to decide on other generic applications by April 11 but the delay was imposed by a US district judge in Washington in order to give Mylan time to seek an emergency order to stop any rivals from launching copycat versions.

The battle over generic Norvasc began last week after the US Court of Appeals reversed an earlier decision that favoured Pfizer in its bid to stop Canadian drugmaker Apotex from launching a generic form of Norvasc (amlodipine). This prompted Mylan, which lost a patent challenge over the drug last month but already had FDA approval to sell a generic version of Norvasc, to claim 180 days of generic marketing exclusivity because it was the first to file with the agency. Apotex contests Mylan’s right to exclusivity and wants to launch its version just as soon as the FDA gives approval.

Judge Ricardo Urbina wrote in his order that he wanted "to ensure that all interested parties have the opportunity to advance their positions to the court on this matter prior to the FDA taking final action on the pending drug approvals.''

Norvasc brought in nearly $4.9 billion in worldwide sales for Pfizer in 2006, $2.7 billion of which came from the USA and Mylan is keen to preserve its position as the only generic competitor on the market, so it can get some of the US giant’s market share without cutting prices too much. However Pfizer has responded by making its own generic amlodipine product available through its Greenstone subsidiary.