Wyeth/Elan shares drop on discouraging side effect profile of AD drug in mid-stage study

Brain-swelling side effects have tarnished investor confidence in Alzheimer's disease drug candidate bapineuzumab. Shares in US drug major Wyeth fell over 10% to $40.50 in after-hours trading on July 29, after detailed Phase II study results were reported at the International Conference on Alzheimer's Disease, held in Chicago, USA. Its partner, Irish drugmaker Elan, lost as much as 29% to 14.55 euros.

Top-line data from the study were reported two months ago (Marketletter June 23) and showed that the beta-amyloid-targeting drug failed to reach statistical significance for the primary endpoint although the firms decided to advance it to late-stage testing anyway.

Detailed analyses of the study, presented at ICAD, showed that, in patients who did not carry the ApoE4 allele, statistically-significant differences from baseline to week 78 were observed in favor of bapineuzumab patients on both cognitive and functional efficacy endpoints: an AD Assessment Scale-Cognitive Subscale treatment difference of 5.0 (p=0.026); Neuropsychological Test Battery treatment difference of 0.35 (p=0.006); and Clinical Dementia Rating Sum of Boxes treatment difference of 1.5 (p=0.04).