Lack of correlation between methotrexate concentrations in serum, saliva and sweat after 24 h methotrexate infusions

1 Methotrexate (MTX) concentrations were studied in serum, mixed saliva and sweat during and after 24 h continuous MTX infusions (0.5-6 g m-2) in 14 patients with various malignant diseases. 2 The serum-MTX concentrations declined in a biphasic manner, but the MTX elimination in saliva and sweat varied to a much greater extent. 3 Saliva/serum and sweat/serum ratios during the MTX infusion were 2.3% and 0.55% respectively. The ratios had increased significantly 20 and 44 h postinfusion. 4 No correlations were demonstrated between salivary- and serum-MTX concentrations during the MTX infusion or 20 and 44 h later. 5 Markedly delayed renal MTX excretions were demonstrated in two patients. In one of them the salivary MTX elimination was also retarded, whereas this was not seen in the other one. 6 We conclude that measurements of MTX concentrations in mixed saliva cannot substitute for serum-MTX determinations in the monitoring of patients after 24 h MTX infusions.