Shares in Amgen and Johnson & Johnson have taken a hit after US regulatory panel recommended a further strengthening of the warning labels on their blockbuster anaemia drugs.

An advisory committee of the US Food and Drug Administration voted 15-2 in favour of having further marketing authorisation of Amgen's erythropoiesis-stimulating agents (ESAs) Aranesp (darbepoetin alfa) and Epogen (epoetin alfa) and J& J's Procrit (also epoetin alfa) be contingent upon adding additional restrictions to the drugs' labels. The panel also voted 17-0 that the companies need to conduct additional clinical trials of the drugs to demonstrate their safety.

Amgen shares slumped following the panel's recommendation, closing down more than 9% at $57.33, while J&J shares slipped 2.5% to end the day at $62.50. The committee’s view came as no surprise given that the FDA recently said that new safety and dosage information needs to be put on the labels of Aranesp, Epogen and Procrit.

The new boxed warnings advise physicians to monitor red blood cell levels and to adjust the ESA dose to maintain the lowest haemoglobin level needed to avoid the need for blood transfusions and physicians and patients are being warned to carefully weigh the risks of these products against transfusion risks.