Engraftment failure following bone marrow transplantation in children with thalassemia major using busulfan and cyclophosphamide conditioning.

Thirteen children older than 3 years of age with beta-thalassemia major underwent allogeneic bone marrow transplantation (BMT) from a full human leukocyte antigen (HLA) matched sibling donor in a single institution. These patients received busulfan (Bu). 16 mg/kg followed by cyclophosphamide (Cy) 200 mg/kg for conditioning. Eight of the 13 patients (Group 1) engrafted and have a median age of 13 years (range 5-15 years). The five patients (Group 2) who failed to engraft have a median age of 6 years (range 3-8 years). The association with the following factors was found to be statistically significant: age (older in Group 1), duration of nadir of white blood count (WBC) of < or = .1 x 10(9)/L (longer in Group 1), and the dose of Bu administered to each patient calculated on the basis of body surface area (higher dose in Group 1). The high rate of engraftment failure (5 out of 13) may be related to the suboptimal systemic exposure of Bu in younger children leading to inadequate bone marrow ablation when the standard dose of 16 mg/kg is used.