MAR 01, 2017 10:34 AM PST

Osteoporosis Drug Causes Micro-Cracks in Bones Instead

WRITTEN BY: Xuan Pham

A drug that’s been prescribed for osteoporosis for over 2 decades isn’t helping bones get stronger. Rather, the drug has been linked to increased incidence of hip fractures. Now, scientists say the root of the problem rests in the microscopic fractures that are caused, paradoxically, by the drug that's supposed to strengthen bones.

Left: normal bones. Right: bones with osteoporosis

Osteoporosis refers to the loss of calcium from bones, leading to thin and brittle bones that are prone to fracture. The condition typically occurs as the body ages and we lose bone mass; this is why osteoporosis may be referred to as the “silent thief.” Osteoporosis is also common in post-menopausal women in whom low estrogen levels seem to accelerate bone loss. The condition can also be brought on by hyperparathyroidism, otherwise known as overactive parathyroid glands.

To combat bone loss, doctors routinely prescribe bisphosphonates, medicines that reduce calcium loss and strengthen bones. These include alendronate (trade name Fosamax) and ibandronate (trade name Boniva). Strangely, though X-rays show increased bone densities from these drugs, doctors didn’t see a corresponding reduction in bone fractures.

"What we wanted to see was whether the bone from bisphosphonate patients was weaker or stronger than bone from untreated controls," said Dr. Richie Abel, the study’s lead author from the Imperial College London.

The research team examined 16 bone samples from patients who suffered hip fractures. Half of the patients had received bisphosphonates, and half had not. They also examined bone samples from people free from osteoporosis and hop fractures as additional control samples.

Using a state-of-art particle accelerator to analyze the bone samples, the team made an eyebrow-raising discovery. They found microscopic cracks in the bone of patients exposed the bisphosphonates. "These microcracks are like the small cracks that emerge when you repeatedly flex a plastic ruler - they gradually weaken the structure and may potentially make it more prone to breaking,” explained Dr. Abel.

People who’ve taken bisphosphonates had 24 percent more microfractures in their bones, as compared to those who haven’t taken the drug. As such, these people had bones that were 33 percent weaker than bisphosphonate-free patients. "Rather startlingly, we found the bone from the bisphosphonate patients was weaker. That's a conundrum because the bone should be stronger,” said Dr. Abel.

The caveat of the findings is the small number of samples in the study. However, the findings appear to be consistent with what doctors and researchers have noticed for years: patients treated with bisphosphonates continue to have weak bones and high incidence of fractures.

"This research suggests that, in a small number of patients, rather than protecting against fractures bisphosphonates may actually may make bones more fragile. We now urgently need larger studies to confirm this finding,” said Dr. Abel. This is especially crucial if they want to change the practice of prescribing bisphosphonates to patients with bone loss and replace it with another more effective therapy.

Additional sources: Imperial College London, BBC

About the Author
  • I am a human geneticist, passionate about telling stories to make science more engaging and approachable. Find more of my writing at the Hopkins BioMedical Odyssey blog and at TheGeneTwist.com.
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