Diabetes Drug Avandia Causes Brittle Bones, Researchers Declare

"These findings have potential clinical implications," the researchers wrote, "as they suggest that long-term rosiglitazone usage in the treatment of Type 2 diabetes and insulin resistance may cause osteoporosis, owing to a combination of decreased bone formation and increased bone resorption."

Researchers monitored the effects on bone breakdown and formation in mice that had been given Avandia. They found that the activity of osteoclasts was increased in the animals, leading to a loss of bone mass.

Osteoclasts are cells that continually destroy old bone in the body. In a healthy body, the same amount of bone is then created by cells called osteoblasts. In the mice taking Avandia, increased osteoclast activity without a concurrent increase in osteoblast activity lead to bone loss.

When the researchers blocked the gene that Avandia targets, however, the mice's osteoclasts failed to mature properly, leading to an increase in bone mass instead. According to the researchers, this suggests a new area of research for treating osteoporosis.

GlaxoSmith Kline has reported a greater risk of hand, upper arm and foot fractures in patients taking Avandia, but a company spokesperson said that GlaxoSmith Kline is not aware of any increase in the spinal fractures that are commonly associated with osteoporosis.

Controversy over Avandia erupted in May, when the FDA issued a warning that the drug raised the risk of heart attack and death among patients taking it. Since that time, prescription of the drug has dropped in the United States, but has continued to increase in parts of Europe. More than 1.5 million prescriptions for rosiglitazone and the related drug pioglitazone were given out in 2006.