Pharmacokinetics of pamidronate in patients with bone metastases.

Abstract

Pamidronate is a second-generation bisphosphonate used in the treatment of tumor-induced hypercalcemia and in the management of bone metastases from breast cancer, myeloma, or prostate cancer. The pharmacokinetics of pamidronate is unknown in cancer patients. To determine the influence of the rate of administration and of bone metabolism, we studied the pharmacokinetics of pamidronate at three different infusion rates in 37 patients with bone metastases. Three groups of 11-14 patients were given 60 mg pamidronate as an intravenous infusion over a period of 1, 4, or 24 hours. Urine samples were collected in the three groups of patients. Plasma samples were obtained only in the 1-hour infusion group. The assay of pamidronate in plasma and urine was performed by high-performance liquid chromatography with fluorescence detection after the derivatization of pamidronate with fluorescamine. The body retention (BR) at 0-24 hours of pamidronate represented 60%-70% of the administered dose and was not significantly modified by the infusion rate. In particular, the BR at 0-24 hours was not reduced at the fastest infusion rate. Among patients, a threefold variability in BR at 0-24 hours occurred, which was related directly to the number of bone metastases and, to some extent, to creatinine clearance. At 60 mg/hour, the plasma kinetics followed a multiexponential course characterized by a short distribution phase. The mean (+/- SD) half-life of the distribution phase was 0.8 hour (+/- 0.3), the mean (+/- SD) of the area under the curve for drug concentration in plasma x time at 0-24 hours was 22.0 +/- 8.8 mumol/L x hours, and the mean (+/- SD) of the maximum plasma concentration was 9.7 mumol/L (+/- 3.2). Pharmacokinetic variables remained unchanged after repeated infusions applied to four patients. Clinically, the three infusion rates were equally well tolerated without significant toxicity. The 1-hour infusion rate could be proposed as kinetically appropriate for the administration of pamidronate to patients with metastatic bone diseases.