Will Glucarpidase After Methotrexate Treatment for Bone Sarcoma Lead to Fewer Side Effects and Reduce Chemotherapy Delays?

Methotrexate is one of the most effective chemotherapy drugs in the treatment of osteosarcoma and some other types of bone sarcoma which are treated the same way as osteosarcoma. However, it frequently leads to sore mouth, tummy pain and increased risk of developing infections. The investigators try to save or "rescue" normal cells from the side effects of methotrexate by giving a drug called folinic acid. Folinic acid is started 24 hours after methotrexate and given regularly until methotrexate levels are really low and not dangerous to normal cells anymore. Despite this rescue, side effects are still a problem and many patients are not well enough to receive subsequent chemotherapy on time. Almost half of the planned chemotherapy cycles are not given on time due to methotrexate side effects. In this study the investigators will examine if adding a drug called glucarpidase to folinic acid is helpful. Glucarpidase is an enzyme that inactivates methotrexate in the blood stream. Lower methotrexate concentration in the blood stream leads to fewer side effects. The investigators would like to see if glucarpidase helps patients to have their chemotherapy on time, by reducing the side effects of methotrexate.