This randomized, double-blind, double-dummy, multicenter trial assessed safety and efficacy of a single dose of IV zoledronic acid (ZOL) 5 mg vs. oral alendronate (ALN) 70 mg weekly in postmenopausal women with low bone mineral density (BMD) who had previously been treated with ALN. Postmenopausal women who were receiving oral ALN for at least 1 year immediately prior to randomization and with lumbar spine or femoral neck BMD T-score values ≤ - 2.0 prior to initiation of ALN were randomized to one 15-min IV infusion of ZOL 5 mg plus 52 weeks of oral placebo (n = 113) or one IV infusion of placebo plus 52 weeks of oral ALN 70 mg (n = 112). End points included percent change in lumbar spine BMD from baseline to month 12 and relative change from baseline in urine N-telopeptide of type I collagen (NTX), serum C-telopeptide of type I collagen (CTX), amino terminal propeptides of type I collagen (PINP), and bone-specific alkaline phosphatase (bone ALP) over 12 months. Adverse events, bone histomorphometry and microscopic appearance, and patient preference for the 2 treatment regimens were also assessed. In this study, a single infusion of ZOL 5 mg maintained BMD 12 months following the switch from oral ALN in women with osteoporosis. The mean duration of prior ALN therapy at baseline was 4 years. Mean biomarker levels in the ALN 70-mg group remained at or close to baseline levels for the duration of the study. In the ZOL 5-mg group, mean biomarker levels were reduced from baseline after 3 months, returned to baseline after 6 months, and increased thereafter but remained within the premenopausal range. The overall rates of adverse events were comparable in the 2 groups (ZOL 5 mg, 86.7%; ALN 70 mg, 80.4%). Headache occurred more commonly within the first 3 days after infusion with ZOL 5 mg (12.4%) than with ALN 70 mg (6.3%). Bone biopsies indicate that both treatments decrease excessive remodeling seen in osteoporosis. The majority (78.7%) of patients expressed preference for once yearly infusion over weekly oral therapy. We conclude that patients can be switched from oral ALN to ZOL 5 mg infusion with maintenance of therapeutic effect for at least 12 months and that patients prefer a once yearly infusion to weekly oral therapy.
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