The gloves came off in the competitive bout for market share in the osteoporosis sector yesterday, after Procter & Gamble Pharmaceuticals and Sanofi-Aventis asked a court to put an end to what they claim is false advertising by rivals GlaxoSmithKline and Roche.

The two firms are upset about a promotional campaign run by GSK and Roche for their Boniva (ibandronate sodium) product, a bisphosphonate drug used to increase bone mineral density in osteoporosis patients. P&G and Sanofi-Aventis, which market a bisphosphonate called Actonel (risedronate sodium), allege that claims made in the advertisements are misleading and inflate the efficacy of Boniva.

GSK and Roche said they stood by the validity of the advertising but could not comment on the lawsuit until details of the complaint were assessed by their legal teams.

Specifically, P&G and Sanofi-Aventis take issue with claims that Boniva has been proven to reduce the risk of non-vertebral fractures, and has efficacy comparable to other bisphosphonates, such as Actonel.

They insist that Boniva was in fact unsuccessful in a clinical trial at reducing fractures affecting the wrist, hip and other bones in women after three years of treatment, and is not approved for this use. Actonel labelling indicates that it has shown efficacy in these fractures at three years, claim the plaintiffs.

“The Boniva label and clinical study data do not support these claims,” said the firms in a statement. Boniva is sold under the trade name Bonviva in some markets.

Both Actonel and Boniva are trying to make gains in a competitive marketplace currently dominated by Merck & Co's $3.2 billion-dollar-a-year market leader, Fosamax (alendronate), approved in the USA in 1995. Actonel has been around since 2000 and has sales in excess of $1 billion, while Boniva debuted in 2003 and has grown slowly, with sales of $13 million for GSK and $28 million for Roche in the first nine months of 2005.

But Boniva had been held back by once-daily dosing, while rivals Actonel and Fosamax are dosed once a week. That changed in March 2005, when GSK and Roche’s product was approved in a once-monthly formulation that should help the product overcome the poor patient compliance that is a feature of bisphosphonate treatment.

Less than half of women are able to tolerate these drugs long term because of complex dosing instructions and gastrointestinal side effects.