Dose dependent effects on bone resorption and formation of intermittently administered intravenous ibandronate

The aim of the present paper was to delineate in detail the dose-dependent effects of intermittent intravenous (IV) ibandronate treatment on the dynamics of markers of bone resorption and formation. The study included 73 healthy postmenopausal women between 50 and 70 years of age. Two groups received an IV injection of either 1 mg or 2 mg ibandronate on day 0 and 84 and one group, which received no treatment, served as control. Study duration was 168 days. Bone turnover was estimated by measuring the serum concentration of the C-terminal collagen I telopeptide (s-CTx, bone resorption) and osteocalcin (s-OC, bone formation) at 19 consecutive time-points. Serum CTx decreased rapidly reaching a nadir 7 days after drug administration. Maximal changes from baseline in the 1 and 2 mg ibandronate groups were -81% and -90%, respectively (P<0.001). However, already 2 weeks after drug administration, s-CTx started to rise again in both treatment groups, reaching -16% and -20% by day 84, i.e. immediately before the second drug administration. In contrast, s-OC showed a slower but progressive decrease over time reaching a nadir at -35% inhibition after 5 months. On a group level, the suppression of bone resorption was greater or equal to the suppression of bone formation at all time points. However, the least significant change (LSC) analysis performed at the individual level highlighted individuals who at certain time points showed apparently greater suppression of formation than resorption, which could also contribute to the inefficacy of this dosing regime. Although the physiological relevance of this latter finding would require further analysis, the results draw attention to the need to optimize the intermittent IV dosing of ibandronate in order to approximate more closely the sustained and balanced anti-resorptive effect provided by daily oral treatment.