Investigation of [6R] 5,10-methylenetetrahydrofolate (Arfolitixorin) as Rescue Therapy for Osteosarcoma Patients Treated With HDMTX.

"The enrolled patients will be treated according to the MAP schedule and will receive the study drug Calcium Folinate commencing 24 hours after the administration of HDMTX and then every 6 hours (q6h) thereafter until the S-MTX levels are ≤ 0.1 µmol/L, in accordance with COG management recommendations.~All patients will receive standard o care (SOC) in the two (2) first HDMTX courses and \[6R\] 5,10-methylenetetrahydrofolate in the two (2) following courses. Patients will be enrolled in two (2) \[6R\] 5,10-methylenetetrahydrofolate dose cohort groups: with \[6R\] 5,10-methylenetetrahydrofolate start dose of 15 mg/m2 (i.e. the same as for SOC rescue) the first cohort will be administered, and 7.5 or 30 mg/m2 in the second cohort."

"The enrolled patients will be treated according to the MAP schedule and will receive the study drug \[6R\] 5,10-methylenetetrahydrofolate commencing 24 hours after the administration of HDMTX and then every 6 hours (q6h) thereafter until the S-MTX levels are ≤ 0.1 µmol/L, in accordance with COG management recommendations.~All patients will receive standard o care (SOC) in the two (2) first HDMTX courses and \[6R\] 5,10-methylenetetrahydrofolate in the two (2) following courses. Patients will be enrolled in two (2) \[6R\] 5,10-methylenetetrahydrofolate® dose cohort groups: with \[6R\] 5,10-methylenetetrahydrofolate start dose of 15 mg/m2 (i.e. the same as for SOC rescue) the first cohort will be administered, and 7.5 or 30 mg/m2 in the second cohort."