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Once-Weekly Risedronate as Effective as Daily: Presented at ENDO

By Paula Moyer

Special to DG News

SAN FRANCISCO, CA -- June 24, 2002 -- One 35 mg weekly dose of risedronate (Actonel) is as effective as 5 mg daily for reducing the risk of vertebral fracture in women with osteoporosis.

Investigators presented these findings here June 21^st at ENDO 2002, the 84^th annual meeting of the Endocrine Society.

Prior research had shown that both dosing regimens are comparably effective at increasing bone mineral density (BMD) and reducing bone remodelling. However, the investigators of a trial evaluation the weekly dose could not assess anti-fracture efficacy due to the absence of a placebo group.

"There is a dilemma in some trials because in certain circumstances it is considered unethical to have a placebo group from whom treatment is withheld," said co-investigator Nelson B. Watts, MD, program director of the Bone Health and Osteoporosis Center at the University of Cincinnati, Ohio, United States. "Since risedronate has been proven to be effective, this is the case in osteoporosis trials involving this medication."

To estimate the efficacy of weekly risedronate in reducing the risk of new vertebral fractures at one year, the investigators constructed a placebo and daily dosage groups by matching patients from the risedronate Phase III vertebral fracture studies to patients in the once-weekly dosage trial.

The inclusion criteria from the once-weekly trial were applied to the Phase III study population. The subjects in the database were women who were at least 50 years old and had completed menopause at least five years before enrolling in the study. Their T-scores were either <-2.5 or <-2 with a prevalent vertebral fracture.

When the investigators compared baseline characteristics, they found a high degree of similarity between the constructed placebo and daily dosage groups, and the weekly-dosage and daily-dosage groups from the weekly-dosage study. The groups' respective mean lumbar spine T-scores ranged from -3.17 to -3.03, and the respective mean ages ranged from 67.6 to 68.1 years. The groups' percentage of subjects with prevalent fractures ranged from 34.8 percent to 35.7 percent.

The incidence of vertebral fractures at one year were 1.2 percent for the weekly-dosage group and 1.5 percent for the daily-dosage group in the weekly-dosage study. In the prior Phase III study, the incidence was 1.7 percent for the daily-dosage group and 5.0 percent for the placebo group. The investigators found no statistically significant difference in fracture incidence for the 5 mg groups from the Phase III and once-weekly studies.

When the investigators compared the weekly-dosage group with the Phase III historical placebo, they found weekly treatment associated with a 77 percent risk reduction in new vertebral fractures within one year (p=0.018). These findings were consistent with the efficacy data on daily risedronate, and suggest that weekly dosage of risedronate at 35 mg is as effective in reducing fracture risk as a daily dose of 5 mg.

"If this model can be confirmed in other analysis, we have a useful way of testing a new dosage or formulation's efficacy without the ethical dilemma of withholding treatment," Dr. Watts said.

Procter & Gamble Pharmaceuticals, the manufacturers of risedronate under the brand name Actonel, sponsored the study. Other than serving as an investigator in the study, Dr. Watts has no financial ties to the company.

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