Merck (NYSE: MRK) is up in pre-market trading as the company announced that its trial for osteoporosis candidate, odanacatib, was stopped early due to robust efficacy vs. placebo, and a favorable risk-benefit profile. Merck telegraphed this announcement fairly well to analysts, which is attributable to the recent run-up in the stock over the past few weeks. Citi upgraded the stock today to Buy from Neutral and raised its price target from $34 to $50, which is also fueling the pre-market activity. Still, the company noted that there are some safety risks with the product candidate that will continue to be monitored in an extension trial. Questions on these safety risks, for which Merck did not give any information, could cap the upside today after the open, in addition to the prior expectations for positive trial results. The extension trial itself means that some patients will stay on drug, and indicates that the safety risks, at this point, are unlikely to be showstoppers. However, these risks may have commercial implications. Merck plans to file for regulatory approval of odanacatib in the U.S., the EU, and Japan in the first half of 2013. Expect shares to trade higher on the open, but level off and potentially trade down on profit taking throughout the day.