Use of matched historical controls to evaluate the anti-fracture efficacy of once-a-week risedronate

Abstract

Placebo controls are essential to assess anti-fracture efficacy of new osteoporosis therapies, but inclusion of a placebo arm in a subsequent clinical trial may be limited by practical or ethical considerations; in these cases, use of an historical control may be appropriate. A recent active-controlled study of risedronate 35 mg once a week demonstrated that this regimen produces increases in bone mineral density (BMD) that are comparable to those seen with the risedronate 5 mg daily dose, which has proven anti-fracture efficacy. To assess the anti-fracture efficacy of this new regimen, we have analyzed the fracture data collected in an active controlled study of risedronate dosing regimens (the Once-a-Week study) using matched historical control data from previous placebo-controlled trials. Women in the Once-a-Week study were matched for age, years since menopause, BMD, and prevalent vertebral fracture status, with placebo patients in the Vertebral Efficacy of Risedronate Therapy (VERT) trials forming an historical placebo group. We also constructed an historical active treatment group from the 5 mg daily arm of the VERT trials for comparison with the 5 mg daily and 35 mg once weekly treatment groups in the Once-a-Week study. Data were obtained from the risedronate 5 mg daily group (n=480) and 35 mg once-a-week group (n=485) in the Once-a-Week study and historical control groups representing daily placebo patients (n=114, matched from 993) and risedronate 5 mg daily patients (n=120; matched from 990) in the VERT studies. Patients received calcium supplementation (1000 mg daily); vitamin D was given if baseline serum 25-hydroxyvitamin D levels were low. Over 1 year, new vertebral fracture risk in the 35 mg once-a-week group was reduced by 77% relative to the historical placebo group (1.2% versus 5.0%; RR 0.23; 95% CI, 0.54 to 0.91, P=0.018), similar to the 1-year risk reduction observed in the VERT trials of risedronate 5 mg daily (61–65%). The incidence of new vertebral fractures in the three active treatment groups was similar: 1.7% in the historical risedronate 5 mg group, 1.5% in the risedronate 5 mg daily group from the Once-a-Week study, and 1.2% in the 35 mg once-a-week group. Risedronate 35 mg once a week appears as effective as the 5 mg daily dose in reducing the risk of new vertebral fractures in the first year of treatment. The use of appropriate historical control data provides an approach to the assessment of fracture effects in osteoporosis trials for which placebo-controlled data are not available.