"A latestage trial of Amgen Incs experimental drug Aimovig found that it reduced episodic migraines by at least half in  percent of patients who had failed up to four previous treatments while  percent of placebo patients achieved that goal the company said on Tuesday.  FILE PHOTO An Amgen sign is seen at the companys office in South San Francisco California October  . The biopharmaceutical company reports earnings on Tuesday. REUTERSRobert Galbraith  The week trial presented this week at the annual meeting of the American Academy of Neurology involved  patients suffering four to  migraine headaches a month who had tried two to four preventive treatments that either did not work for them or had intolerable side effects.  This is a trial in really difficult to treat patients professor Uwe Reuter trial investigator and managing medical director at Charit Universittsmedizin in Berlin told Reuters in a telephone interview. He said previous studies excluded patients who had tried more than two other treatments.  Reuter said the point gap between the treatment and placebo groups was in line with previous Aimovig studies.  Aimovig currently under review by the U.S. Food and Drug Administration is likely to be the first drug in a new class designed to target calcitonin generelated peptide CGRP which plays a key role in migraine activation. A decision by the FDA is due by May .  Amgen has partnered with Novartis AG to cocommercialize Aimovig in the United States while Amgen has rights to the drug in Japan and Novartis has rights to commercialize in rest of world. The drug a monoclonal antibody was given monthly by injection at a dose of  mg for the trial.  Similar drugs are under development at companies including Eli Lilly  Co and Teva Pharmaceutical Industries Ltd but Amgen emphasizes that Aimovig is the only one that targets the CGRP receptor pathway rather than CGRP itself.  Aimovig has the potential to help fill treatment gaps in more difficult patient populations whose migraine has not been adequately managed with current therapies Sean Harper executive vice president of research and development at Amgen said in a statement.  Amgen said Aimovig trial patients also had statistically and clinically meaningful improvements in secondary trial goals including fewer monthly migraine days and better physical function.  Researchers said no Aimovig patients stopped treatment due to side effects while around  percent of placebo patients discontinued because of side effects.  Analytics firm GlobalData has forecast that CGRP antibodies will generate combined sales of  billion by .  Reporting by Deena Beasley Editing by Lisa Shumaker Our StandardsThe Thomson Reuters Trust Principles. httpthomsonreuters.comenaboutustrustprinciples.html"