The pharmacokinetics and safety of twice daily i.v. BU during conditioning in pediatric allo-SCT recipients

Intravenous BU divided four times daily (q6 h) has been shown to be safe and effective in pediatric allo-SCT recipients. Though less frequent dosing is desirable, pharmacokinetic (PK) data on twice daily (q12 h) i.v. BU administration in pediatric allo-SCT recipients is limited. We prospectively examined the PK results in a cohort of pediatric allo-SCT recipients receiving i.v. BU q12 h as part of conditioning before allo-SCT. BU levels were obtained after the first dose of conditioning. PK parameter analysis ( n =49) yielded the following 95% confidence intervals (CI 95 ): weight-normalized volume of distribution: 0.65–0.73 L/kg; t 1/2 : 122–147 min; weight-normalized clearance (CL n ): 3.4–4.3 mL/min/kg; and area under the curve: 1835–2180 mmol × min/L. From these results, a steady state concentration was calculated with CI 95 between 628–746 ng/mL. Comparison between recipients ⩽4 vs >4 years old revealed significant differences in t 1/2 (mean: 115 vs 146 min, P =0.008) and CL n (mean: 4.4 vs 3.5 mL/min/kg, P =0.038). Intravenous BU q12 h had a comparable PK to i.v. BU q6 h PK seen in the literature, and in pediatric allo-SCT recipients, is a feasible, attractive alternative to i.v. q6h dosing.