A clinical trial has provided evidence that Protelos (strontium ranelate) - a drug for osteoporosis developed by French drugmaker Servier - has a dual mode of action that distinguishes it from other drugs for the disease.

The results of the bone biopsy study back up earlier suggestions that Protelos combats osteoporosis by stimulating bone synthesis and inhibiting its breakdown. Far from being a static tissue, bone is constantly being created and destroyed, and current drugs for osteoporosis either block bone breakdown or stimulate its growth.

The European Commission approved Protelos in 27 countries for the treatment of post-menopausal osteoporosis last October, after results from the SOTI (Spinal Osteoporosis Therapeutic Intervention) trial showed that the agent reduced the risk of vertebral fractures in women 49% after one year. The product has also been launched in its first markets, including the Germany, Ireland, the UK, Spain and Italy.

The latest five-year study showed that Protelos stimulated the activity of bone-building osteoblast cells while inhibiting osteoclasts that carry out bone resorption. It also revealed that Protelos is safe when given for an extended period of time and stimulates the production of normal healthy bone. The creation of areas of softer, weaker bone has been seen after long-term treatment with some members of the widely-used bisphosphonate class of osteoporosis drugs.

“This is the first study of bone biopsies which shows clearly that treatment with Protelos is safe and does not alter the bone structure,” said lead investigator Prof P D Delmas of Claude Bernard University in Lyon, France. The results were presented at the annual American Society of Bone and Mineral Research conference over the weekend.

However, despite its promising profile, Protelos‚ use in the UK remains under question, with fears that its cost could restrict patient access. In August, the Scottish Medicines Consortium restricted use of the drug to high-risk patients, including those who cannot take bisphosphonates, are aged over 75 years and have already had a fracture, as it said equivalent cost-effectiveness to bisphosphonate therapy has not been shown. Meanwhile, the National Institute for Health and Clinical Excellence is not due to rule on the drug’s use in England and Wales until March 2006.

More than one-third of adult women will sustain one or more osteoporotic fractures in their lifetime.