Long-term treatment of osteoporotic women with bisphosphonates does not impair the response to subsequently administered intravenous pamidronate.

Abstract

We addressed the question whether the response of osteoporotic patients to bisphosphonate treatment is reduced with time. Bisphosphonate-treated women with postmenopausal or glucocorticoid-induced osteoporosis showed adequate and consistent changes of bone markers to subsequently administered intravenous pamidronate. Response of osteoporotic patients to bisphosphonates is not impaired during their long-term administration. Inadequate response to bisphosphonate treatment has been described in patients with Paget's disease of bone but has not been addressed in osteoporosis although treatment failure is a clinically relevant problem. Twenty one women with postmenopausal osteoporosis (PMO) aged 68 ± 8.2 years and 14 women with glucocorticoid-induced osteoporosis (GIOP) aged 65 ± 10 years were treated with tri-monthly intravenous infusions of 45 mg of pamidronate for 1 year. All patients had been previously treated with bisphosphonates (alendronate, risedronate, pamidronate) for a mean period of 6.2 years (range, 1.3-14 years). Blood samples were taken for measurement of the bone resorption marker C-terminal crosslinking telopeptide of type I collagen (CTX-I) on days 1 and 4 and of the bone formation marker procollagen type I N propeptide, (P1NP) on day 1 of every tri-monthly treatment course. With each treatment course there was a significant decrease in serum CTX-I on day 4 and an increase to baseline values 3 months after each infusion in both PMO (mean values, day 1: 291.33 ± 160.78 pg/ml vs. day 4: 131 ± 91.7 pg/ml, p < 0.001) and GIOP (day 1: 219.3 ± 114.8 pg/ml vs. day 4: 98.8 ± 51.6 pg/ml, p < 0.001). Serum P1NP remained stable during the whole year of treatment. Long-term bisphosphonate treatment of women with either PMO or GIOP does not impair the response to subsequently administered intravenous pamidronate suggesting that inadequate response to long-term bisphosphonate treatment is not responsible for treatment failure.