More bad news from drugmakers trying to develop treatments for Alzheimer’s disease: Yesterday, Baxter announced that its mixed-antibody therapy failed to reduce cognitive decline in patients with mild to moderate Alzheimer’s disease. As I reported back in July 2012, the company saw positive results in a small four-patient trial of the treatment. None of these patients showed any cognitive decline, leading some experts to hope that the disease can be stopped or slowed (see “Study Suggests Alzheimer’s Disease Can be Stabilized”). But when Baxter tested its potential treatment—a complex mixture of antibodies harvested from healthy donated blood—in nearly 100-times as many Alzheimer’s patients, the company did not find a rate of decline slower than patients given a placebo.

Baxter’s announcement comes less than a year after two other pharmaceutical companies revealed that their Alzheimer’s treatment candidates failed in large clinical trials (see “Another Bust for Alzheimer’s Drugs” and “A New Setback for Alzheimer’s Drugs”). Both of these company’s trials tested antibodies known to glom onto the plaque protein amyloid-beta (it’s not clear what protein, or proteins, Baxter’s mixed antibody treatment would target). What drug makers are getting wrong is not clear—it could be  timing (many experts believe treatments will need to start early in the course of the disease, perhaps even before cognitive decline begins, to be effective), or it could be that amyloid is not the right target (the cause of the disease and amyloid’s role are not set in stone). What is clear is that with each year, we are facing a larger problem: Currently, around 36 million people worldwide have Alzheimer’s. That number is expected to grow to 2 billion by 2050 (see “The Dementia Plague”).