Safety and efficacy of l-leucovorin rescue following high-dose methotrexate for osteosarcoma.

High-dose methotrexate with leucovorin rescue (HDMTX-LCV) is an important component of regimens used in the treatment of osteosarcoma. As of this writing the commercially available form of leucovorin is a racemic mixture of d- and l-diastereoisomers; the l-isomer is the active component. This study describes the efficacy and safety of l-leucovorin in HDMTX-LCV regimens. Fifteen patients with osteosarcoma who were enrolled into or treated according to Pediatric Oncology Group protocols 8759 and 8651 received l-leucovorin (7.5 mg every 6 hours) in place of d,l-leucovorin following high-dose methotrexate. Safety data were collected for 1 week after each course or until any toxicities resolved. The mean number of l-leucovorin doses per course was 16.2 and the mean total dose per course was 126 mg. Adverse experiences were generally mild or moderate and occurred in 54 (60%) of 90 courses of l-leucovorin therapy. One l-leucovorin patients, who had inadequate methotrexate rescue, developed severe typhlitis. There were no instances of severe, acute methotrexate toxicity. Myelosuppression was seen but, in general, was not severe. These results support the conclusion that l-leucovorin effectively rescues patients from the toxicity of high-dose methotrexate.