More than 70% of postmenopausal women with osteoporosis prefer treatment with Roche/GlaxoSmithKline’s monthly Bonviva to Merck & Co’s weekly Fosamax because they find the treatment easier to take in the long term.

These results of the BALTO II study - presented for the first time at the Sixth European Congress on Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ECCEO) late last week in Vienna - echo data from BALTO I revealed last September.

Roche and GSK will see BALTO II results as a plus for Bonviva (ibandronate) - currently the only once-monthly oral treatment for osteoporosis - especially as patient preference studies have been important drivers in the widespread switch from daily to weekly dosing.

Bisphosphonate drugs such as Bonviva, Fosamax (alendronate) and Actonel (risedronate) from Procter & Gamble/Sanofi-Aventis currently represent the gold-standard osteoporosis treatment, but patient adherence is notoriously low because of these drugs' gastrointestinal side-effects and complicated dosing regimens.

P&G/Sanofi-Aventis hit back during ECCEO, citing not only evidence that patients prefer effectiveness over dosing regimen but also data demonstrating that Actonel almost halves the risk of hip fracture in women with osteoporosis aged up to 100 years.

Advertising claims about Bonviva’s efficacy in reducing the risk of non-vertebral fractures is currently the subject of a legal dispute between P&G/Sanofi-Aventis and Roche/GSK.

Roche/GSK will also welcome two-year data reported at ECCEO from the DIVA study, which confirms earlier results announced last year indicating that intravenous (IV) Bonviva every three months significantly improved bone mineral density (a marker of fracture risk) compared to daily treatment.

Presenting the results in Vienna, lead investigator Professor Pierre Delmas, Lyon, France, commented that IV Bonviva is likely to be particularly suitable for elderly women who are at high risk of fracture and who are already taking several drugs for co-existing health problems.

Despite the positive spin for Bonviva, there is, as yet, no evidence that a switch to longer dosing intervals will necessarily translate into improved patient adherence in real-life clinical practice. Proof may be provided by the ongoing PERSIST study, which is comparing once-monthly and weekly regimens of Bonviva, but in the meantime the war of words looks set to continue in the osteoporosis market.

From Sue Lyon at ECCEO in Vienna