Whole body retention in relation to rate of bone resorption after intravenous bisphosphonate (pamidronate) in patients with breast cancer and bone metastases

881 Background: Bisphosphonates (BPs) given i.v. every 3 to 4 weeks are effective in the management of metastatic bone disease from breast cancer but responses among patients vary and it is not known whether current dose and dose intervals are appropriate for an individual patient. An influence of PK of BP on its antiresorptive action may contribute to this variation. To test this hypothesis we determined the skeletal retention of intravenous pamidronate and its association to the rate of bone resorption in patients with bone metastases from breast cancer. Methods: In a cross-sectional study, 24 hr urinary excretion of pamidronate and NTx were measured in 40 patients with bone metastases from breast cancer at the beginning, after 3–6 months or after 1 year of treatment with iv pamidronate 90 mg every 3–4 weeks. Results: Skeletal retention (= dose –amount excreted into urine) varied between 12–98% (mean 62%) of the administered dose but there were no differences in retention between patients receiving pami...