Amgen has pulled out of a co-development deal it had with AstraZeneca for an experimental psoriasis drug, which was in the late stages of clinical development, after observing "suicidal ideation" in some patients during clinical testing of the new drug candidate. Dr. Sean E. Harper , executive vice president of research and development at Amgen, said the company believed the likelihood of the drug being required to carry warning labels of suicide risk would limit the potential market for the treatment.