Reliability of a pretransplant i.v. BU test dose performed 2 weeks before myeloablative FluBu conditioning regimen

A pretransplant test dose of i.v. BU was previously used in pediatric patients undergoing a reduced-intensity allogeneic hematopoietic SCT (HSCT). Here, we used a BU test dose in 23 adult patients who were not pancytopenic and underwent a myeloablative allogeneic HSCT prepared with fludarabine and i.v. BU (FluBU). Pharmacokinetics (PK) of BU were calculated after a test dose (0.8 mg/kg) was performed 2 weeks before transplant. Targeted BU area under the curve (AUC) range was 4800-5200 microM min. The mean BU dose calculated after the test dose was 3.5+/-0.5 mg/kg. To validate the test dose, PK studies were repeated in 17 patients after the first dose of BU during the conditioning regimen. An AUC below the therapeutic value of 4000 microM min was observed in 23% of the patients receiving a wt-based dose and in 0% of patients whose dose was calculated on the basis of the test dose (P=0.03). In patients who had a test dose, a significant correlation (P<0.0001) between the first and subsequent doses of BU during the conditioning regimen was observed. Our findings may allow more centers to pursue transplant strategies with targeted BU by overcoming the time limitation for PK studies during the conditioning regimen.