Long-lasting effect of pamidronate on bone metabolism in osteoporosis after stopping therapy.

AIM OF THE STUDY To determine whether and when, like after estrogen withdrawal, bone loss resumes once disodium pamidronate is discontinued, even after long duration therapy. MATERIALS AND METHODS 19 patients with osteoporosis, previously treated for 4.3 -/+ 0.5 years (SEM) with oral cyclical intermittent pamidronate, were followed-up for 30.3 -/+ 2.2 months after withdrawal from therapy. Lumbar spine and proximal femur BMD was measured by DXA (QDR-1000, Hologic Inc., Waltham, MA). RESULTS Lumbar spine BMD did not change significantly for the first 2 years, but decreased 1.8 % in the 3rd year (p<0.001). The proximal femur BMD did not change significantly for 3 years. The biological parameters of bone remodelling increased progressively with elapsing time, due to the underlying loss of pamidronate protection. CONCLUSIONS after withdrawal of pamidronate therapy, a residual protecting effect was observed at the proximal femur and at the lumbar spine for 2 to 3 years. The time-interval resurgence of bone remodelling and the bone loss observed at the spine in the 3rd year suggest that there is no risk of freezing bone with pamidronate therapy, even at high doses. A long-lasting protective effect on bone mass can be expected. Periods of therapy with an active drug, interrupted by long resting periods, may produce the same protective effect as continuous therapy, owing to the levelling-off effect on bone mass observed after the first two years while on therapy. This would lead to lower expenses for a course of therapy.