Long-Term Bisphosphonate Use Linked to Atypical Fracture Risk

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Bisphosphonate medicines help prevent bone loss and make bones stronger. Bisphosphonates usually are given to postmenopausal women at risk of osteoporosis or who have already been diagnosed with osteoporosis.

In October 2010, the U.S. Food and Drug Administration (FDA) told doctors about a link between bisphosphonates and the risk of breaking a leg bone in an unusual spot. Doctors call this "atypical femur fracture." The femur is the large leg bone that runs from your hip to your knee.

A study published in the February 23, 2011 issue of the Journal of the American Medical Association showed that atypical femur fracture risk was nearly 3 times higher in postmenopausal women who took a bisphosphonate for more than 5 years compared to postmenopausal women who took a bisphosphonate for about 3 months or less. Still, the overall risk of atypical femur fracture -- no matter how long a woman took a bisphosphonate -- was very low.

Researchers looked at the medical histories of Canadian women who were 68 years old or older and who had taken an oral bisphosphonate (pill taken by mouth). The women were prescribed one of three bisphosphonates:

  • Actonel (chemical name: risedronate)
  • Fosamax (chemical name: alendronate sodium)
  • Didronel (chemical name: etidronate)

The researchers focused on women who had any type of broken femur -- typical or atypical -- since starting to take a bisphosphonate.

Typical femur fractures are breaks in or close to the "neck" of the femur, the part of the bone that connects the femur to the hip. Breaks in this part of the femur are called femoral neck or intertrochanteric fractures.

Atypical femur fractures are breaks below the neck of the femur, in the part of the bone between the hip and the knee. Breaks in this part of the femur are called subtrochanteric or shaft fractures.

The researchers then looked for links between the risk of either type of femur fracture and the length of time a woman had been taking a bisphosphonate.

The researchers found 9,723 typical femur fractures in the women in the study. Bisphosphonates help prevent bone loss and make bones stronger. So the researchers expected that the longer a woman took a bisphosphonate, the less likely she'd be to have a typical femur fracture. This was the case.

Compared to women who took a bisphosphonate for fewer than 100 days, the risk of a typical femur fracture was:

  • 7% lower in women who took a bisphosphonate for 100 days to 3 years
  • 14% lower in women who took a bisphosphonate for 3 to 5 years
  • 24% lower in women who took a bisphosphonate for 5 years or longer

The researchers found only 716 atypical femur fractures in more than 50,000 women in study. While the risk of a typical femur fracture was lower when a woman took a bisphosphonate for a longer period of time, the opposite was true for atypical femur fracture risk. The longer a woman took a bisphosphonate the MORE likely she was to have an atypical femur fracture. Women who took a bisphosphonate for 5 years or more were 2.7 times more likely to have an atypical femur fracture compared to women who took a bisphosphonate for fewer than 100 days.

Still, atypical femur fractures were very rare, no matter how long a woman took a bisphosphonate. Of 52,595 women who took a bisphosphonate for 5 years or more, atypical femur fractures happened in only 22 out of every 1,000 (0.22%) women during the sixth or seventh year of bisphosphonate treatment.

It's likely that the risk of atypical femur fractures also increases with long-term use of other bisphosphonates that weren't considered in this study.

The other oral bisphosphonate is:

  • Boniva (chemical name: ibandronate)

Intravenous bisphosphonates are:

  • Aredia (chemical name: pamidronate)
  • Bonefos (chemical name: clodronate)
  • Boniva (chemical name: ibandronate)
  • Reclast and Zometa (chemical name: zoledronic acid)

Most doctors believe that the very small risk of atypical femur fracture is outweighed by the overall bone-strengthening benefits -- including a lower risk of typical femur fractures -- of bisphosphonates for many postmenopausal women. Still, the higher risk of atypical femur fractures with long-term use of bisphosphonates means more research is needed to better understand how long bisphosphonates should be taken to balance the benefits and the risks.

If you're a postmenopausal woman, your doctor may recommend a bisphosphonate to strengthen your bones or treat osteoporosis. You may already be taking a bisphosphonate to help improve your bone strength. In either case, you might want to talk to your doctor about this study and a long-term treatment plan that makes the most sense for you.

Bisphosphonates need to be taken in a specific way and may cause serious side effects. If you're prescribed a bisphosphonate, make sure you and your doctor talk about how to take the medicine.

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