Effects of once-monthly oral ibandronate on serum ctx levels: results of a 3-month randomized trial

Abstract

Aims: Once-monthly oral ibandronate does not maintain stable reduction in bone resorption, suggesting that some persons taking the drug may have little reduction in turnover for at least part of the dosing interval. Because the extent of reduction in turnover is correlated with clinical efficacy of bisphosphonates, this may have important clinical consequences. To explore this question, we examined the proportion of participants who reached specified threshold levels of resorption marker reduction. Methods: Postmenopausal osteoporotic women participated in a 3-month, randomized, double-blind, placebo-controlled clinical trial. Enrolled participants were randomized to receive ibandronate 150 mg or 100 mg or matching placebo every 4 weeks for 3 doses. Serum CTx was measured just prior to each dose, one week after each dose, and weekly for 4 weeks after the final dose. Geometric mean percent change from baseline was calculated, as was the proportion of participants who had marker reductions of at least 40%, 50%, and 60% at each time point after the third dose (Weeks 9–12). Results: At each week after dosing a progressively smaller proportion of women met the defined sCTx reduction thresholds. Fewer than half of women taking 150 mg of ibandronate had sCTx reductions of at least 60% at all 4 weeks after the third dose (Weeks 9–12) and fewer than three-quarters (71.9%) of women had reductions of at least 40% at all four weeks. Conclusions: With once-monthly dosing of oral ibandronate, the proportion of women who attain specified reductions in sCTx declines progressively with time between doses. Because the observed cyclic changes in bone resorption might affect efficacy, the possible clinical implications of intermittent dosing deserve further study.