The two drugs are members of a class of drugs known as bisphosphonates, as is a newer drug, Roche's Boniva.
But is this really the case?
Nelson B. Watts, MD, director of the University of Cincinnati Bone Health and Osteoporosis Center, joined a team of internationally renowned experts in an effort to find out.
The researchers analyzed insurance records for 12,215 postmenopausal women who took Actonel and 21,615 women who took Fosamax for the first time. The women were 65 and older.
The result: After a year of treatment, women taking Actonel had 43% fewer hip fractures and 18% fewer non-spine fractures than women taking Fosamax.
"This adds to the suggestion from clinical trials that Actonel works faster than Fosamax," Watts tells WebMD. "We found a significantly lower rate of fracture at hip and non-vertebral sites for patients given Actonel vs. Fosamax at both six and 12 months.
"I am not saying one drug is better than the other -- only that Actonel works faster," Watts says.
The study -- sponsored by Procter & Gamble and Sanofi -- appears in the current online issue of the journal Osteoporosis International.
Procter & Gamble, Merck, Roche, and Sanofi are WebMD sponsors.
Slice of Life -- but Not Proof Positive
Watts is quick to point out that the study is not a clinical trial and therefore cannot be taken as conclusive proof.
But the study impresses Holly Thacker, MD, director of the Women's Health Center at The Cleveland Clinic.
Thacker, who was not involved in the study, notes that Watts and colleagues looked at the kind of women doctors see in real life. Moreover, they evaluated the endpoint that really matters to women suffering bone loss -- actual bone fractures.
"I tend to prescribe Actonel more often than Fosamax, so this study is reassuring," Thacker tells WebMD.
"We now have some excellent drugs for bone loss. In the bisphosphonate family, I rank Actonel No. 1, with Fosamax a close second," she says. "I rank Boniva a distant third, because it has not yet been shown to reduce hip fracture."
All things being equal, Watts and Thacker would prescribe Actonel over Fosamax.
But both of these top doctors point out that not all women are equal. Some women may tolerate one drug better than another. Or their insurance may pay more for one than the other.
In either case, women will get the most benefit from the drug that works best for them.
Watts notes that bone-loss drugs should be taken for many years. But most patients stop taking them after six or seven months -- greatly reducing their potential benefit.
"When we start someone on osteoporosis treatment, we hope they will continue taking it for years," Watts says.
"But bone loss is a silent disease -- like high blood pressure or high cholesterol. Until something happens, the disease doesn't make them feel bad, and the drug doesn't make them feel better. That is sometimes hard for people to accept," he says.
Thacker, too, stresses the importance of long-term treatment. Unlike Watts, who usually begins drug treatment only when a woman has frank osteoporosis, Thacker begins as soon as she detects bone loss.
"Once you're starting to lose bone mass, you need to be on treatment," Thacker says.
"First, we make sure a woman is getting enough calcium and vitamin D," Thacker says. "But if she is, and she's still losing bone mass, we start treatment. It is a long-term commitment. The chances are, you will be on it for a long time."