Effect of body weight on the pharmacokinetics of cyclophosphamide in breast cancer patients

Cyclophosphamide pharmacolinetics have been studied in 16 female patients with advanced breast cancer. The group included 7 patients who were >20%, ≤30% over ideal body weight and 5 patients who were >30% over ideal body weight. Cyclophosphamide plasma elimination half-lives ranged between 152 and 984 min (mean 457 min), the apparent volume of distribution between 19.1 and 62.31 (mean 36.11), and plasma clearance between 25.9 and 166.6 ml/min (mean 69.5 ml/min). There was a significant positive correlation (r=0.624, P=0.010) between body weight and plasma elimination half-life, and a significant negative correlation between body weight and cyclophosphamide clearance when normalized to body surface area (r=0.578, P=0.019) or normalized to ideal body weight (r=0.531, P=0.0345). the apparent volume of distribution did not correlate with body weight. The results show that cyclophosphamide disposition is altered in patients with increased body weight.