Enzyme Immunoassay of Methotrexate in Blood and Its Stability in Infusion Solution

Abstract

Therapeutic drug monitoring procedures after high-dose methotrexate (MTX) therapy were studied with enzyme homogeneous immunoassay technique (EMIT). MTX levels in serum of osteosarcoma patients administered intravenously 200-300 mg/kg dropped below 10μM in 24 hours after the initiation of the therapy.
Ultrafree filtration method was used for the separation of the drug in free form from the protein-bound form in serum. The ratios of free to total MTX levels were approximately 0.60 in 0.1-650μM of total MTX levels. MTX monitored with EMIT is clinically useful to prevent or reduce its toxicity. MTX in infusion solution was susceptible to photodecomposition with the addition of vitamin B₂.