AstraZeneca is to stop all development work on its fledgling respiratory drug motavizumab, resulting in a $445m impairment charge this quarter.Astra had already flagged up this possibility and has been considering the future of motavizumab since August when the US Food and Drug Administration asked for an additional clinical trial for the drug to show that its benefits outweighed the risks. Astra said that it has now requested withdrawal of the Biological License Application (BLA) for motavizumab in cases of serious respiratory syncytial virus (RSV) disease. It holds intangible assets of $445m relating specifically to motavizumab and these will now be written off.The disappointment comes just days after the drugs giant was hit by a new delay to its blood-thinning treatment Brilinta, as the US authorities wanted more analysis of its clinical trial. Brilinta had been expected to get approval to launch in the US.