The findings of a new study may explain how the side effects of Fosamax and similar bone-strengthening drugs cause abnormal femur fractures, which typically occur following little or no trauma, such as falling from standing height or less.
Researchers with Cornell University and the Hospital For Special Surgery in New York indicate that a class of drugs known as bisphosphonates may actually attack and degrade mechanisms in cortical bone that are intended to make bones tougher. The findings were published recently in the Proceedings of the National Academy of Sciences (PNAS).
Fosamax is the most widely used medication in this class, introduced by Merck for treatment and prevention of osteoporosis, and now widely available as generic alendronate sodium. While the drug has been used by millions of individuals strengthen bones and reduce the risk of fractures associated with osteoporosis, it has been linked to a number of side effects, including bone fractures and osteonecrosis of the jaw.
This latest study focuses on those atypical femur fractures (AFFs) which involve unusual breaks following minimal trauma where the bone would not typically breask. Researchers compared bone biopsies from 50 women, 33 who suffered bone fractures and 17 who did not, but underwent total hip arthroplasty.
According to the findings, women who had suffered femur fratures while taking a bisphosphonate had bone tissue that was harder and more mineralized; essentially making the bone more brittle. The findings also showed that women taking drugs like Fosamax had lower fracture toughness, lower crack-initiation toughness, and had less crack deflection.
“Here we examine bone tissue from women with AFFs and show that long-term bisphosphonate treatment degrades the fracture-resistance toughening mechanisms that are inherent to healthy bone,” the researchers noted. “Our work resolves the apparent paradox of AFFs as a side effect of the most common osteoporosis treatment by clarifying the differing effects of bisphosphonates on bone tissue structure and mechanical properties across multiple length scales.”
Merck has faced thousands of Fosamax lawsuits in recent years, in which former users alleged that the drug maker failed to adequately warn consumers and the medical community about serious risks associated with the aggressively marketed and widely used medication. In 2013, Merck agreed to pay nearly $30 million in Fosamax settlements to resolve more than 1,100 jaw injury lawsuits, brought on behalf of individuals who experienced painful and debilitating deterioration of the jaw.
Merck also faced several thousand lawsuits brought by individuals who suffered a sudden bone fractures following long-term use of the medication. Although the litigation was initially dismissed by the lower court on summary judgement, a decision by the U.S. Court of Appeals for the Third Circuit reinstated the fracture litigation in March.