Long-term control of bone turnover in Paget's disease with zoledronic acid and risedronate

A single 5-mg infusion of zoledronic acid restores biochemical markers of bone turnover into the reference range in the majority of patients with Paget's disease and maintains biochemical remission for at least 2 years. This effect is largely independent of pretreatment disease activity and prior bisphosphonate therapy.

Zoledronic acid (ZOL) is a potent bisphosphonate that produces a rapid and complete control of the increased bone turnover of Paget's disease. Long-term control of disease activity is an important aim of treatment in the hope that this will reduce the risk of complications such as deformity, fracture, and degenerative joint disease.

This study compares the ability of ZOL 5 mg given as a 15-minute intravenous infusion with risedronate (RIS) 30 mg daily by mouth for 60 days to maintain long-term control of bone turnover. No bisphosphonate was given during the extension study. All patients (n = 296) who achieved a therapeutic response, defined as normalization or a >75% reduction in the total alkaline phosphatase (total ALP) excess above the midpoint of the reference range, were eligible for inclusion.

ZOL maintained the mean level of total ALP at the middle of the reference range, whereas those treated with risedronate showed a linear increase in total ALP from the 6-month post-treatment time-point. Both treatments resulted in a linear relationship between the 6-month nadir and 24-month total ALP. The relationship for RIS was shifted upward, showing that for a given level of post-treatment biochemical activity, bone turnover increased with time. This was in contrast to the ZOL-treated patients where total ALP generally remained unchanged over this 18-month extension period. A similar pattern of response was seen with the other bone turnover markers.

ZOL maintains bone turnover within the reference range over 24 months from the initiation of treatment. A reduction in the incidence and severity of long-term complications may require persistent normalization of bone turnover over many years, and this now seems a realistic possibility with ZOL.