Having lost a patent case over its blockbuster blood pressure drug Norvasc, Pfizer has begun selling a generic version of its own medicine just as Mylan Laboratories launched its copycat of the product.

This spate of launches was provoked by the decision at the end of last week by the US Court of Appeals for the Federal Circuit which 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 US Food and Drug Administration 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. It has therefore begun shipping 2.5mg, 5mg and 10mg tablets of amlodipine, which brought in nearly $4.9 billion in worldwide sales for Pfizer in 2006, $2.7 billion of which came from the USA.

Pfizer has responded to Mylan’s announcement by saying it is making available its own generic amlodipine product immediately through its Greenstone subsidiary and added that it will “continue to pursue all available legal remedies” to protect the market for Norvasc through a six-month paediatric exclusivity period that expires in September 2007. Branded Norvasc will also remain on the market but the new version, which does not need FDA approval, is likely to be sold at a cheaper price to compete with Mylan's copycat drug.

Novartis’ Exforge may benefit from patent loss

The patent loss on Norvasc could prompt Novartis to speed up the introduction in the USA of Exforge, which combines amlodipine with the Swiss firm’s own Diovan (valsartan), according to Bloomberg. Novartis had planned to launch Exforge, in September but “we are reviewing the situation,'' Novartis spokesman John Gilardi told the news agency, and he also noted that the firm will stop paying royalties to Pfizer for Lotrel, which combines Norvasc and Novartis' Lotensin (benazepril).

UBS analyst David Beadle said in a note that an earlier launch of Exforge by Novartis could “cement its dominance of the US hypertension market.