High dose methotrexate (HDMTX) with folinic acid rescue is widely used to treat osteosarcoma, which predominantly afflicts children; the study investigated HDMTX pharmacokinetics (pk) in adult subjects in neoadjuvant/adjuvant settings. Twenty five patients with advanced osteosarcoma (11 females - 14 males, median age 26.0 years) were treated by 12 g/m 2 HDMTX 4 hour iv infusion (64 total courses, range 1-7 courses). Pk was determined by non-compartmental analysis and population pk modeling. Median (range) bioavailability pk parameters were: Cmax (maximum MTX concentration) 1149.5 μM (692-2 200), AUCtot (total area under curve) 6 955.1 μmol*h/l (3 477-12 681). Cmax > 1 000 μM gave increased histological responses (p el). Toxicity was mild: only two reversible G4 events were observed, related to AUQ tot > 12 000 μmol*h/l (p max/AUCtot and subject age/sex was found, even in the population pk model. The excretion mechanism is not affected by sex/age differences. HDMTX can safely be administered to adults: as in younger patients, a good clinical response can be predicted by Cmax, while severe toxicity depends on highest AUCtot values.
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