Women taking the diabetes drug rosiglitazone are at increased risk of bone thinning, according to a new study being presented Wednesday, June 18, at The Endocrine Society’s 90th Annual Meeting in San Francisco.

Previous research showed that treatment with rosiglitazone (marketed under the brands Avandia, Avandamet, and Avandaryl) increases fractures in women with type 2 diabetes, but not in men taking the drug. Scientists thought the main reason for the increased fracture risk in women was that rosiglitazone decreases bone formation, the making of new bone.

However, the new study, from the University of Texas (UT) Southwestern Medical Center in Dallas, found that the drug increases bone resorption, which is the breakdown of bone. When bone breaks down faster than the body makes new bone, the result is bone loss. Bone loss eventually can lead to the bone-thinning disease osteoporosis and to broken bones.

The UT Southwestern researchers studied 111 diabetic patients who participated in the Dallas Heart Study, a multiethnic study of patients in Dallas County funded by the National Institutes of Health and the Donald W. Reynolds Foundation. Sixty-six men and 45 women randomly received either rosiglitazone or an inactive placebo for 6 months. Neither the patients nor the investigators knew which patients received the active drug.

“At the end of 6 months, women who took rosiglitazone had a 33 percent increase in bone breakdown,” said coauthor Ugis Gruntmanis, MD, Chief of the Endocrinology Division at the Dallas VA Medical Center and associate professor of medicine at UT Southwestern. “This increase occurred regardless of age.”

Unlike in other reported studies, women taking this diabetes drug showed no change in bone formation, Gruntmanis said. Men who took rosiglitazone had no change in either bone breakdown or bone formation.

Whether they took the active drug or the placebo, African-American men and women had higher bone turnover than did whites or Hispanics. Bone turnover is the joint process of bone resorption and bone formation.

“Women who are taking rosiglitazone must be aware that this drug can make bones thinner,” Gruntmanis said. “Because postmenopausal women have a higher risk of decreased bone density and fractures as a result of lack of estrogen, their doctors should check their bone density before they start this drug.”

For this study, GlaxoSmithKline provided placebo and rosiglitazone, and Biosite Inc. supplied assays.

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Founded in 1916, The Endocrine Society is the world's oldest, largest, and most active organization devoted to research on hormones and the clinical practice of endocrinology. Today, The Endocrine Society's membership consists of over 14,000 scientists, physicians, educators, nurses and students in more than 80 countries. Together, these members represent all basic, applied, and clinical interests in endocrinology. The Endocrine Society is based in Chevy Chase, Md. To learn more about the Society, and the field of endocrinology, visit our web site at www.endo-society.org.