But the company has said that it will not need to carry out any additional clinical trials of Mircera to satisfy the FDA, suggesting that the hold-up could be short. The news comes just one week after Amgen, which is currently the only manufacturer of EPO drugs in the US, was turned down by the Supreme Court in an appeal related to its long-standing EPO patent infringement case with Shire and Sanofi-Aventis. Shire has no plans to enter the US market with its rival product Dynepo (epoetin delta), but observers suggest that Amgen's monopoly on anaemia drugs in the US market could end within the next few months following approval for Mircera. In this particular case, it is possible that the issues raised by the FDA relate to the agency's ongoing class review of renal anaemia agents, and on technical matters relating to how Mircera might comply with new labelling requirements for these drugs. Roche has clearly stepped closer to bringing Mircera to the market, but the Swiss company is still locked in a patent infringement lawsuit that Amgen filed against it in March 2005. Patent litigations are often convoluted, and while Amgen remains confident in protecting its intellectual property, Roche insists on the fact that it is not infringing any valid patent with Mircera. If Roche were to go ahead and launch after an FDA approval but before the patent litigation is resolved, it lays itself open to the risk of substantial damages should the litigation go Amgen's way. The approvable letter for Mircera comes at a time in which the FDA is also monitoring the use of EPO drugs to treat anaemia in cancer patients, after an increasing number of studies have unveiled negative effects of these drugs in this setting. Recently, an FDA committee issued an alert informing medical professionals and patients about cases of severe anaemia in cancer patients taking Amgen's Epogen (epoetin alfa) and Aranesp (darbepoetin alfa). However, these recommendations only apply to the oncology setting and they will not impact approval of Roche's Mircera, since the company is initially only targeting its drug to dialysis patients. If Mircera finally makes it into the US market, it has a competitive profile compared to the drugs currently available, according to Roche. Mircera has a longer half-life, it says, which means that it needs to be injected with less frequency than the other drugs. While Mircera is expected to be effective in correcting the anaemia in chronic kidney disease (CKD) patients with dosing every two weeks, Amgen's Epogen needs to be injected as often as three times a week. Aranesp, on the other hand, is approved for dosing once every one, two or three weeks, depending on the indication. Roche refused to comment on the issues related to Mircera approvable letter. But Citigroup analyst Yaron Werber said he anticipates the most likely outcome of the upcoming FDA advisory committee meeting is a recommendation for adding restrictions on labelling that would affect the entire EPO drug class. Regarding the effect on Amgen, Werber is less concerned about competition from Mircera and more concerned about potential reimbursement changes that could lead to sales erosion following the safety concerns that have emerged with Epogen and Aranesp.