Let’s take one problem at a time. First, there are fresh concerns over potentially troubling safety data from a late-stage study of the biotech’s drug for postmenopausal osteoporosis, known as denosumab. Wall Street is worried because results show the med increased bone density in both early and late stage postmenopausal women, but patients had a higher rate of infections requiring hospitalization.

Amgen says its investigators don’t believe the higher infection rate is related to the drug, noting that additional studies involving patients undergoing cancer therapy, who are typically more susceptible to infection, didn’t yield higher infection rates. Just the same, Amgen shares fell. “We caution…that if not a regulatory risk, such data included in an eventual product label could limit the commercialization potential,” Wachovia Capital Markets analyst George Farmer wrote in an investor note, according to Reuters.

Separately, US Senator Chuck Grassley wants Amgen to explain why some physician groups received higher rebates for purchasing its Aranesp anemia med. In a letter to Amgen, the Iowa Republican writes that data he obtained from Amgen indicated oncologists in some states were given much higher rebates than others for Aranesp, which is also under scrutiny by a House committee.