Pamidronate distribution in pediatric renal and rheumatologic patients

Objective: To evaluate the distribution and elimination of pamidronate in a population of pediatric patients with renal and rheumatologic disease. Methods: Pamidronate whole blood levels were collected for the first 4 h after first exposure in 7 patients. The relationship between the rate of urinary excretion of pamidronate and bone formation or resorption was examined in 18 patients while receiving pamidronate at a total dose of 1 mg/kg/dose infused intravenously over a 4-h period. The urinary pamidronate clearances were correlated with renal function, calcium levels and measures of bone formation and resorption. Results: Pamidronate levels reached steady state concentrations of 0.9-1.5 μg/ml within 30 min and the clearance of the drug (mean±SE) from blood was 180.0±64.2 ml/kg/h with an elimination half-life of less than 1 h. The mean urinary excretion of 31.5±2.2% of the administered dose indicated that about 68% of the drug was incorporated into bone, confirming the uptake of pamidronate into bone was similar in pediatric patients compared to that previously reported for adults. Bone specific alkaline phosphatase, which is a marker for bone growth and formation, had significant correlation with the uptake of pamidronate into bone (p=0.002). No correlation was demonstrated with a marker for bone resorption (urinary N-telopeptide/creatinine ratio), or with creatinine clearance or calciuria when assessed 2 months after treatment. Conclusion: Pamidronate at a dose of 1 mg/kg/dose every 2 months appears safe in the short term for pediatric patients, achieves relatively low whole blood pamidronate levels, and has similar skeletal uptake of pamidronate compared to adults.