Merck's patent claims for once-weekly administration of alendronate sodium (Fosamax) are invalid and obvious, according to the US Court of Appeals for the Federal Circuit in Washington DC. The verdict that the biggest-selling form of the drug is not covered by patent protection through to 2018 as previously thought hinged on Merck's use of the word 'about'.

The appellate court overturned the previous decision of the Delaware district court in August 2003, which found that Merck's US patent (5,994,329) was infringed by Teva Pharmaceuticals' Abbreviated New Drug Application (ANDA) filing. The district court determined that the claim term 'about' used to describe dose size was redefined by the patentee. The wording was intended to take into account variations in the molecular mass of the different derivatives of alendronic acid in order to deliver the exact dose stated.

Teva appealed the court's claim construction, and the Federal Circuit agreed, ruling that the term 'about' should be given its ordinary and accepted meaning of 'approximately', and not to mean 'exactly'. The court stated that when a patentee acts as his own lexicographer in redefining the meaning of particular claim terms away from their ordinary meaning, the patentee must clearly express that intent in the written description.

The district court's decision had discounted one piece of prior art that had been published in Lunar News, because the article was not published in a peer-reviewed journal or authored by one skilled in the relevant art. The federal circuit overturned this decision because the Lunar News article, which had clearly suggested once-weekly dosing to avoid or minimize problems related to dosing frequency, was written by one skilled in the art and that Lunar News was widely distributed among those working in the osteoporosis field.

In a strongly worded dissent, Judge Rader warned that the lexicographer option should be taken at one's own risk. Agreeing with the district court, Judge Rader wrote that Merck defined the phrase in question with precise values, but fell five letters short of success because the phrase included the word 'about'. He thought that the appellate court cast aside the lexicographer rule without a convincing explanation.

Teva believes that as a result of this ruling its ANDA will be eligible for final approval in February 2008 when Merck's original chemical matter patent (US 4,621,077) expires following its paediatric exclusivity period.