[JURIST] The US Court of Appeals for the Federal Circuit [official website] ruled [PDF opinion] Friday that the patent for the once-a-week version of Fosamax [medical information], the second best selling drug produced by Merck & Co. [corporate website], is invalid. Fosamax currently dominates the market for treatment of osteoporosis. Under the ruling, generic competitors could release their version of the drug within three years rather than waiting until 2018. Fosamax has been lucrative for Merck, with 2004 sales totaling $3.16 billion. The ruling came the say day that Merck formally acknowledged it was under investigation by the SEC in connection with its withdrawal of arthritis blockbuster Vioxx [JURIST report] after research studies found it to be dangerous [Vioxx consumer info]. After heavy trading on the NYSE Friday, Merck shares were down 11.8 percent. AP has more.